What HVAC differences apply between Build-to-Rent and conventional strata apartment buildings?

Build-to-Rent has four defining HVAC differences. First, single-ownership operating economics — the BTR operator retains every apartment for 20 to 30 years and pays the operating energy bill, so capex spent on heat recovery ventilation, MERV 13 filtration, demand-controlled basement, low-leakage ductwork and BMS metering returns directly to the asset. Strata apartments by contrast are sold individually and the developer has weak incentive to over-spec the HVAC. Second, BTR is required to provide and operate substantial communal amenity — gym, co-working, cinema, pet wash, dining, sometimes pool — every one of which is a separate HVAC sub-system with its own AS 1668.2 ventilation and acoustic specification. Third, BTR tenancy turnover drives a higher specification on cleanable, durable, low-maintenance ductwork because every apartment changeover is an inspection and clean cycle. Fourth, the Build-to-Rent Industry Standards published by the Property Council of Australia provide a voluntary specification overlay that goes above NCC minimum on indoor environment quality including outdoor air rate, filtration and bathroom exhaust — most institutional BTR projects specify to PCA BTR Industry Standards on top of NCC.

What HVAC requirements apply to retirement village independent living units versus assisted living?

Retirement village independent living units (ILUs) are Class 2 SOUs and follow the standard apartment HVAC stack — AS 1668.2 SOU exhaust, residential range-hood ventilation, individual reverse-cycle split or VRV plant. Assisted-living units and serviced apartments in a retirement-living context typically remain Class 2 in NCC classification but the operator-specified HVAC pushes harder on filtration (MERV 13), continuous low-rate bathroom exhaust regardless of occupancy, redundant reverse-cycle to manage residents with impaired thermoregulation, and acoustic targets in line with AS/NZS 2107 recommended NC-30 for sleeping rooms. Aged-care nursing homes (Class 9c) are a separate building classification with a separate HVAC stack — see the SBKJ aged care, retirement and disability HVAC duct guide.

Insights · Multi-Residential and Mixed-Use

High-Rise Apartment, Build-to-Rent, Student Accommodation, Retirement and Mixed-Use Class 2 HVAC Duct Guide

An engineer-led HVAC ductwork specification guide for Australian Class 2 multi-residential projects — high-rise apartment towers, Build-to-Rent (BTR), purpose-built student accommodation, retirement village independent and assisted living, and mixed-use podium retail, office and amenity. Covers the NCC Class 2 sole-occupancy unit stack, AS 1668.1 fire and smoke management (stair pressurisation, corridor smoke spill, basement smoke clearance), AS 1668.2 ventilation (SOU kitchen, bathroom, laundry, common-area, basement car park, EV charging Li-ion zone), AS 4254 ductwork, AS 1530.4 fire-rated penetrations, AS 4072 multi-residential fire and smoke barriers, AS 2107 acoustic targets, NCC Section J, NABERS Multi-Unit Residential and Green Star Multi-Unit Residential ratings, the Property Council of Australia Build-to-Rent Industry Standards, the Australian Apartments Industry Code, BTR resident amenity (gym, co-working, cinema, pet wash, communal kitchen), and the SBKJ machinery footprint that mechanical contractors use to fabricate it. Written for the apartment developer, BTR operator, mechanical services consultant, building surveyor, and Class 2 high-rise builder working on the next decade of Australian multi-residential supply.

By SBKJ Engineering Team · Published May 15, 2026 · 38 min read · Reviewed by SBKJ QA & Engineering

Why Class 2 multi-residential is its own HVAC discipline

A high-rise apartment tower or Build-to-Rent building is the most heterogeneous repeat-typology HVAC project in commercial construction. A single 30-storey Class 2 tower in Melbourne or Sydney typically contains 200 to 400 sole-occupancy units across 25 to 28 residential floors, a 2,500 to 4,000 m² basement car park spread across two or three levels, a 1,500 to 3,000 m² mixed-use podium with ground-floor retail and Class 5 office on level one, a 500 to 1,200 m² resident amenity floor with gym, lounge, dining and sometimes a swimming pool, a rooftop plant deck with the smoke management fans and tower discharge stacks, and a network of vertical risers, fire-rated shafts, smoke spill ducts and pressurisation ducts that connect everything. Each of those sub-buildings has different occupancy patterns, different ventilation rates, different acoustic criteria, different humidity loads, different fire and smoke compartmentation requirements, and a different operator at the handover end. Co-ordinating them into a single coherent HVAC system that meets NCC Class 2, AS 1668.1, AS 1668.2, AS 4254 and a dozen other standards is the art of Class 2 multi-residential mechanical design.

Five characteristics make Class 2 multi-residential HVAC fundamentally different from single-house residential, hotel, commercial office or aged-care HVAC.

Per-apartment privacy and tenant control expectation. Every apartment is a private dwelling under separate tenancy. The HVAC system that crosses the apartment threshold from a common riser must respect that boundary — no cross-tenant odour migration, no cross-tenant acoustic transfer through return paths, no cross-tenant infection-control failure during a respiratory event. Each apartment must have independent temperature, humidity and ventilation control to the resident's preference. This drives the dominant SOU HVAC architecture of per-apartment split or VRV reverse-cycle, per-apartment range-hood exhaust to a vertical riser, per-apartment bathroom exhaust to a vertical riser, and per-apartment laundry exhaust path.

Vertical-riser-dominated duct architecture. Unlike a commercial office tower where horizontal ductwork on each floor dominates the duct volume, an apartment tower's ductwork is concentrated in vertical risers — SOU kitchen exhaust risers, SOU bathroom exhaust risers, SOU laundry exhaust risers, corridor supply and return risers, stair pressurisation risers, smoke spill risers, basement extract risers all running floor to floor across the full tower height. The risers are typically galvanised steel with TDF flange joints, sized in a single duct width per floor and stepping up at floor groupings to manage the cumulative flow. Riser shaft sizing is set at structural design and is irreversible after slab pour.

Fire and smoke compartmentation density. Class 2 buildings have the highest density of fire and smoke separating elements of any commercial typology — every SOU wall is a 60/60/60 minimum fire-rated separating wall, every floor slab between SOUs is a 90/90/90 or 120/120/120 separating slab, every stair shaft is fire-isolated and pressurised, every lift shaft is fire-isolated, every services shaft is fire-rated, and every penetration of any of these elements requires an AS 1530.4 fire damper or fire-rated wrap. A 200-apartment Class 2 tower typically has 1,500 to 3,000 fire dampers in the HVAC system, each one of which must be commissioned, drop-tested and registered for AS 1851 annual maintenance.

Operating-cost-bearing party varies by tenure. In a strata sell-down apartment building, the apartment owner pays the electricity bill for the in-apartment HVAC and the body corporate pays the operating cost of the common-area HVAC (corridor, lobby, lifts, basement, rooftop plant). In a Build-to-Rent building, the BTR operator pays both. In purpose-built student accommodation, the operator pays both. This split drives capex-versus-opex trade-offs across the project — a developer building for strata sell-down has weak incentive to spend capex on common-area energy efficiency because the body corporate inherits the bill, whereas a BTR operator has very strong incentive to spec heat recovery ventilation, low-leakage ductwork and demand-controlled common-area systems because they keep the asset for 20 to 30 years and pay the operating cost.

Post-pandemic indoor environment quality expectation. The Class 2 multi-residential sector has internalised the post-pandemic expectation of higher outdoor air rates, MERV 13 minimum filtration, and demonstrable air change in common areas. The Property Council of Australia Build-to-Rent Industry Standards (published 2022, updated 2024) sets explicit indoor environment quality targets that exceed NCC minimum on outdoor air, filtration, bathroom exhaust and humidity control. Premium strata apartment developers increasingly match the BTR specification to support sale prices and the apartment-rating disclosure that some states now require.

Building classifications across a mixed-use Class 2 project

A modern Australian Class 2 high-rise is rarely a single classification. The NCC mix on a typical 30-storey project includes:

Class 2 — the sole occupancy units, occupying floors 4 through 30 in a typical podium-plus-tower configuration. Each SOU is a dwelling. Class 2 has its own specific ventilation, fire and acoustic provisions.
Class 5 — any office tenancy in the podium. Common on mixed-use sites where the developer has secured an anchor office tenant for level 1 or 2.
Class 6 — ground-floor retail tenancies including cafe, restaurant, convenience store, fitness centre with a retail trading element, and small format shops. The interface with the residential tower above is one of the more delicate parts of the HVAC scheme.
Class 7a — the basement car park, typically two to three levels covering 2,500 to 4,000 m².
Class 9b — assembly buildings, which captures any communal amenity space above the resident-only threshold, gymnasium tenancy, function space, indoor recreation, and certain BTR communal lounges where the occupant load triggers Class 9b classification.
Class 9c — aged-care residential service, applicable only where the project includes a co-located nursing home or memory-care wing. Most retirement villages are Class 2 for independent living units and Class 9c only for the nursing-home component. See the aged care, retirement and disability HVAC duct guide for Class 9c specifics.

The NCC mix matters at HVAC design stage because every classification boundary is a fire-compartmentation boundary, a smoke-management zone boundary, and frequently a ventilation-rate boundary. The mechanical services consultant maps the classifications to the HVAC zoning at concept design and locks the boundaries before riser shaft locations are finalised in structural design.

Australian Class 2 multi-residential market and major operators

The Australian apartment, Build-to-Rent, student accommodation and retirement village sectors are dominated by a manageable list of operators whose specifications drive most of the new-build mechanical engineering work in the country. Understanding each operator's preferences shortens the design cycle considerably.

Build-to-Rent operators

Mirvac (ASX:MGR) is the Australian BTR pioneer through its LIV by Mirvac portfolio. The completed LIV stock now spans Newstead in Brisbane (the first Australian institutional BTR opened in 2020), Anstey in Melbourne, Sydney Olympic Park, the Pearl development, and South Yarra in Melbourne. The Mirvac BTR engineering standards push hard on indoor environment quality including 10 L/s per person SOU outdoor air, MERV 13 filtration as default, energy recovery ventilation at the building level, demand-controlled basement, and a substantial communal amenity HVAC programme covering gym, co-working, dining, cinema and pet wash. The standard volume is the largest single source of BTR HVAC specification in the Australian market.

Greystar is the US BTR pioneer (the largest apartment operator in the US by units) which entered Australia through the Sydney and Melbourne markets and absorbed the AXA IM Alts BTR portfolio in 2023. Greystar's Australian BTR developments include South Yarra and Fishermans Bend in Melbourne and the Sydney South project, with a development pipeline of over 5,000 units announced. The Greystar engineering standard imports the US BTR specification template adapted for Australian climate, NCC and AS 1668 compliance — typically NC-30 apartment bedrooms, full DOAS with energy recovery, MERV 13 filtration, dedicated AHUs per amenity sub-zone, and a structured pre-occupancy commissioning programme.

Hines is the US developer-operator behind the Apex BTR programme in Australia, with developments announced in Brisbane and Sydney. Hines' specifications follow a similar template to Greystar with a focus on energy and indoor environment quality metrics that translate to the global Hines ESG reporting framework.

Cbus Property develops BTR under the Element brand (in joint venture with Local Real Estate as Element Build to Rent / Local Build To Rent). Cbus is one of the largest Australian superannuation-fund-backed developers and its BTR pipeline includes multiple Melbourne and Sydney projects, each with mechanical engineering specifications targeting the higher end of the PCA BTR Industry Standards.

Salta Capital, Sentinel, Lendlease (ASX:LLC), Cromwell Property, and Investa are additional active BTR developers in the Australian market. Each has internal mechanical engineering standards that go beyond NCC minimum, typically targeting NABERS Multi-Unit Residential 5 to 5.5 stars and Green Star Multi-Unit Residential 5 stars or higher.

Apartment developers (strata and BTR)

Meriton is the largest apartment developer in Australia by volume — a private NSW-based group that has delivered tens of thousands of apartments across Sydney, Brisbane and the Gold Coast since the 1960s. Meriton's volume builder mechanical engineering standard is pragmatic, code-compliant and focused on per-apartment HVAC simplicity — split-system reverse-cycle in every habitable room, the AS 1668.2 SOU exhaust stack at minimum or modest premium, and a straightforward galvanised duct riser scheme. The volume drives a continuous procurement of HVAC ductwork in tens of thousands of square metres per year.

Mirvac develops strata apartments alongside the LIV by Mirvac BTR portfolio. The strata mechanical specification typically sits between the Meriton volume standard and the LIV BTR standard — better than minimum code, not as aggressive as BTR on common-area energy.

Lendlease develops apartments as part of its diversified property business and on large urban regeneration sites including Barangaroo (Sydney), One Sydney Harbour, Melbourne Quarter, Victoria Cross over the station, and the Sydney Place / Salesforce Tower precinct. The Lendlease apartment specifications target premium price points and carry corresponding HVAC premiums.

Multiplex (Brookfield-owned), Crown Group (NSW), TOGA Group (NSW), Westacott (NSW), Sammut Developments, ICD Property Group, Bensons Property (Melbourne), Central Equity (Melbourne), Pellicano (Melbourne), Frasers Property Australia, and Brookfield Multiplex round out the major Australian apartment developer list. Each runs a continuous pipeline of strata apartment projects feeding mechanical contractor demand for SOU-stack ductwork.

Purpose-built student accommodation

Scape is the largest private purpose-built student accommodation operator in Australia, with a portfolio of over 16,000 beds across Sydney, Melbourne, Brisbane and Adelaide following its acquisition of Urbanest and consolidation of the Atira portfolio. Scape's engineering specification is the dominant PBSA standard in Australia — 10 to 12.5 L/s per occupant outdoor air, MERV 13 filtration, individual heating-cooling at the room level, communal study lounge and dining at AS 1668.2 commercial rates with demand-controlled ventilation, and a 24/7 operating model that drives capex on durable galvanised ductwork.

Iglu Student Accommodation operates a substantial Sydney, Melbourne and Brisbane portfolio with engineering specifications closely tracking Scape. UniLodge is the largest university-affiliated operator in Australia and operates a mix of university-owned and PBSA-style assets. Yugo is the Scape-derived global brand operating select Australian assets. Journal Student Living is a newer entrant in the Melbourne PBSA market.

Retirement villages and over-55s

Aveo (Brookfield-acquired) is the largest Australian retirement village operator by unit count. The Aveo portfolio spans more than 90 villages across the country, with each village typically including 100 to 400 independent living units (Class 2), a community centre (Class 9b), and frequently a co-located aged-care nursing home (Class 9c). Aveo's mechanical specification for the independent living units follows a high-end Class 2 apartment specification with additional considerations for resident thermoregulation, accessibility, and the AS 1428 corridor and lobby standards.

Levande (Stockland-owned), IRT Group, ECH Inc, Calvary Retirement Communities, Bolton Clarke, Estia Health (ASX:EHL) and Regis Healthcare (ASX:REG) are the next major operators in the retirement-living space. Each runs a parallel development programme that drives substantial Class 2 HVAC ductwork procurement.

Mixed-use podium and serviced apartment operators

The mixed-use podium of a residential tower frequently includes a serviced-apartment brand or a hotel-style operator. Mantra Group (Accor) operates serviced apartments under Mantra, Peppers and BreakFree. Quest Apartment Hotels operates serviced apartments under the Quest brand. Meriton Suites is Meriton's vertical-integrated serviced apartment operator. Adina and Oaks operate adjacent product. Each operator brings its own engineering specification overlay for the serviced-apartment portion of the building.

Major Australian builders for Class 2 high-rise

The Class 2 high-rise construction market in Australia is dominated by John Holland (CIMIC Group), Multiplex, Built (Lendlease), Hutchinson Builders, ICON, Roberts Pizzarotti, and a number of state-level mid-tier builders. Each carries internal HVAC subcontractor relationships that drive the procurement of ductwork machinery and fabrication services on each project.

Major Class 2 multi-residential projects driving HVAC specification

The reference projects listed below are the benchmark Australian Class 2 multi-residential HVAC schemes that newer projects are typically compared against.

LIV Munro, Melbourne (LIV by Mirvac)

LIV Munro is Mirvac's flagship Melbourne BTR delivered above the new Queen Victoria Market on a 49-storey tower designed by Bates Smart, comprising 490 apartments across studio, one, two and three-bedroom configurations. The mechanical scheme is a textbook contemporary Australian BTR specification — per-apartment ducted reverse-cycle with concealed indoor units, energy recovery ventilation supplying tempered outdoor air to every SOU, MERV 13 filtration on the recovery ventilator, AS 1668.2 SOU exhaust risers in galvanised G275 with TDF flange joints, residential range-hood exhaust to a dedicated stainless-lined riser, a substantial communal amenity floor including gym, co-working, dining, cinema and pet wash with each amenity on its own AHU, and an extensive demand-controlled basement ventilation system serving the underground car park.

LIV Indigo, Sydney Olympic Park (LIV by Mirvac)

LIV Indigo is the first major institutional BTR completed in Australia, opened in 2020 in Sydney Olympic Park as a 315-apartment scheme. The mechanical scheme established many of the standards now common in Australian BTR — full DOAS, energy recovery, MERV 13 filtration, lined supply duct to apartment bedrooms for NC-30 acoustic, and a comprehensive communal amenity HVAC scheme.

Greystar Melbourne (South Yarra)

Greystar's South Yarra BTR project (announced 2022, completing in stages 2025 to 2027) is one of the largest single Australian BTR developments at over 700 apartments across two towers. The mechanical specification imports the Greystar US BTR engineering standard adapted for Australian compliance, with particular emphasis on indoor environment quality, communal amenity programming, and a structured pre-occupancy commissioning protocol.

Element Build to Rent (Cbus Property)

Element BTR developments span Melbourne and Sydney sites and are characterised by the Cbus institutional-investor focus on long-term operating performance. Mechanical specifications target NABERS Multi-Unit Residential 5 to 5.5 stars and Green Star Multi-Unit Residential 5 stars.

Meriton Sundale, Gold Coast

Meriton's Sundale development on the Gold Coast is representative of the high-volume Meriton apartment specification — a 51-storey tower with over 500 apartments, code-compliant SOU mechanical scheme with split-system per habitable room and AS 1668.2 SOU exhaust at minimum, with the volume-builder discipline of standardised drawings across multiple Meriton projects to drive duct fabricator efficiency.

One Sydney Harbour (Lendlease)

One Sydney Harbour at Barangaroo is a Renzo Piano-designed three-tower luxury residential development by Lendlease comprising over 800 apartments. The mechanical specification matches the luxury price point — VRV centralised refrigerant per apartment, lined supply duct to NC-25 in the bedrooms of premium and penthouse apartments, full DOAS with energy recovery, MERV 13 filtration as default, and a substantial rooftop amenity including pool and lounge with corresponding HVAC scheme.

Aveo Newstead (Brisbane)

Aveo Newstead is a representative contemporary Aveo retirement village delivered as a 200-unit independent living tower with co-located community amenity and assisted-living component. The mechanical scheme is Class 2 SOU specification with the retirement-living overlay — higher filtration, continuous low-rate bathroom exhaust, redundant reverse-cycle in the assisted-living wing, and AS 1428 accessibility coordination across all common areas.

Scape Berkeley (Melbourne)

Scape Berkeley in Carlton is a flagship Scape Student Living development providing over 600 student beds across studio, en-suite and shared configurations. The mechanical scheme is the Scape PBSA template — individual reverse-cycle per room, dedicated SOU exhaust with humidity-boost, common-area study lounge and dining at AS 1668.2 commercial rates with demand-controlled CO2-based ventilation, and a substantial back-of-house operations area.

Iglu Brisbane City

Iglu Brisbane City is a 700-bed PBSA tower with the Iglu engineering specification — closely tracking Scape with similar SOU and common-area provisions.

Atria, Melbourne (Mirvac)

Atria is Mirvac's earlier Melbourne strata apartment development representative of the contemporary Mirvac strata specification — premium Class 2 SOU with ducted reverse-cycle, AS 1668.2 SOU exhaust with operator overlay, and a substantial communal amenity floor.

Standards and codes for Class 2 multi-residential HVAC

Australian Class 2 multi-residential HVAC projects sit at the intersection of multiple overlapping regulatory frameworks. The mechanical engineer's first task on any project is to confirm which of the following apply and at what level.

Building classification and structure

NCC Volume One Part F4 — the Australian National Construction Code provisions for ventilation in Class 2 to Class 9 buildings. Sets the AS 1668.2 reference and the Verification or DTS pathway to compliance.

NCC Volume Two Section 3.12 — the equivalent provisions for Class 1 residential (single dwellings) — referenced here because the Class 2 mechanical engineer frequently coordinates with Class 1 townhouse or terrace components in a mixed development.

NCC Section J — energy efficiency provisions. For multi-residential Class 2 buildings, Section J covers approximately 25 to 40 percent of the total energy compliance, with the balance in building fabric, glazing and lighting. The HVAC contribution is concentrated in duct R-values, duct seal class, AHU efficiency, chiller plant efficiency, and BMS metering.

Ventilation and indoor air quality

AS 1668.2-2012 (updated) — the Australian standard for mechanical ventilation. Sets the SOU kitchen exhaust at 40 L/s wet vapour, SOU water closet exhaust at 25 L/s, SOU shower exhaust at 30 L/s, SOU laundry exhaust at 25 L/s, common corridor outdoor air at 10 L/s per person, basement car park ventilation at 1 L/s per m² or equivalent demand-controlled, and the residential general outdoor air via window or compliant trickle vent.

AS/NZS 1668.2 SOU range-hood provisions — the specific provisions for residential range hoods in sole occupancy units, including capture velocity, exhaust path and compliant termination.

ASHRAE Standard 62.2 — the international residential ventilation standard, referenced by some BTR operators with international parent companies as an additional indoor air quality overlay above AS 1668.2.

Fire and smoke management

AS 1668.1 — fire and smoke control in mechanical ventilation. Sets construction, leakage and integrity requirements for stair pressurisation (50 Pa minimum overpressure, 1.0 to 8.0 m/s through one open door, 110 N maximum door opening force), corridor smoke spill and smoke clearance, zone smoke control, and the smoke-rated ductwork classification.

AS 1530.4 — fire test method for service penetrations including fire dampers and fire-rated wraps. Sets the FRL classification of fire dampers and fire-rated duct wrap systems.

AS 4072.1 and AS 4072.3 — multi-residential fire and smoke barriers, specifically the service penetration sealing systems for fire and smoke separating elements between sole occupancy units in Class 2 buildings.

AS 1851 — annual fire damper inspection, testing and maintenance. The HVAC contractor hands the AS 1851 register to the building manager at practical completion as the basis for ongoing damper drop-testing.

AS 1670 — fire detection and alarm systems. Coordinates with the HVAC fire-mode control logic.

AS 2118 — automatic fire sprinkler systems, applicable to most Class 2 buildings above the NCC sprinkler threshold.

Ductwork

AS 4254.1 — rectangular HVAC ductwork standard.

AS 4254.2 — round HVAC ductwork standard.

Both standards set construction, gauge, joint and leakage class requirements for galvanised, stainless and aluminised steel ducts at the typical Class 2 multi-residential pressure classes.

Acoustic

AS/NZS 2107:2016 — recommended indoor sound levels. Table 1 sets the recommended NC range by space type, with apartment bedrooms NC-30 to NC-35, apartment living areas NC-35, corridors NC-35 to NC-40, gymnasium NC-40 to NC-45.

AS 1276 — acoustic test method, applicable to commissioning measurement of NC levels in completed apartments.

Accessibility

AS 1428.1 — design for access and mobility. Sets the corridor widths, door clearances, lift lobby dimensions, and accessible bathroom requirements that the HVAC scheme must coordinate with. Diffuser placement, grille placement and access panel placement must not conflict with the accessibility envelope.

AS/NZS 1428.4 — wayfinding for the vision-impaired, applicable to common-area signage including identification of HVAC plant room access doors.

ADAAG — the US Americans with Disabilities Act Accessibility Guidelines, referenced by international BTR operators as an additional accessibility overlay.

Lifts, services and confined-space

AS 1735 — lifts and escalators. Coordinates with the lift shaft ventilation, motor room ventilation and lift pit ventilation under AS 1746 confined-space provisions.

AS 1657 — platforms, walkways and ladders, applicable to access to rooftop mechanical plant and concealed plant rooms.

AS 1746 — confined space entry, applicable to lift pit, plant room and basement riser entry for HVAC maintenance.

Electrical and gas

AS/NZS 3000 — the Australian and New Zealand wiring rules.

AS/NZS 3008 — the Australian and New Zealand cable sizing standard.

AS 5601 — LPG gas installation, applicable to apartments with LPG cooking and to the LPG storage and distribution for any podium retail tenancy with gas cooking.

BTR and apartment industry codes

Property Council of Australia Build-to-Rent Industry Standards — voluntary specification overlay published by the PCA for the BTR sector, including indoor environment quality targets, communal amenity provisions, and operating performance expectations.

Australian Apartments Industry Code — an industry self-regulation code published by industry bodies covering apartment design quality, common-area provision, and operating performance.

Property Council Multi-Unit Code — an additional industry code for multi-unit residential development.

Department of Planning and Environment (state-specific) — each state in Australia has its own planning department that publishes design quality guides for apartment developments. The NSW Apartment Design Guide (SEPP 65) is the most prescriptive in the country and sets minimum apartment areas, ceiling heights, natural ventilation, natural light and storage provisions that the HVAC scheme must coordinate with. Victorian Better Apartments Design Standards (BADS) and Queensland equivalent are similar but less prescriptive.

Energy efficiency and rating tools

NABERS Multi-Unit Residential — the Australian rating tool for the common-area performance of multi-unit residential buildings. Rates whole-of-building common-area energy and water per apartment per annum.

NABERS Apartment Energy — the per-apartment variant rating individual apartment energy performance.

Green Star Multi-Unit Residential — the Green Building Council of Australia rating product specific to multi-unit residential, covering a broader set of sustainability dimensions including IEQ, materials and management alongside energy.

Federal and state BTR-specific framework

Federal Build-to-Rent Tax Incentives — the Albanese government's Build-to-Rent housing reform package introduced from 2024 provides preferential tax treatment to qualifying BTR developments. Eligibility criteria include minimum unit count, operating duration, affordable-housing component and indoor environment quality benchmarks that align with the PCA BTR Industry Standards.

State-specific BTR concessions — Victoria, NSW and Queensland have each published state-level BTR concession packages including land tax surcharge waiver, foreign investor surcharge waiver and stamp duty relief subject to compliance with state BTR criteria.

Workplace exposure standards relevant to Class 2 multi-residential operations

Safe Work Australia publishes Workplace Exposure Standards (WES) that set the maximum allowable concentrations of airborne contaminants in occupied environments. The Class 2 multi-residential HVAC designer references the following WES values:

Carbon dioxide (CO&sub2;) — 5000 ppm 8-hour time-weighted average (TWA). In an apartment context CO&sub2; tracks occupancy and is the primary indicator for demand-controlled ventilation in common areas. Premium and BTR specifications typically set the CO&sub2; control setpoint at 800 to 1000 ppm, well below the WES, to support claims on indoor environment quality.
Methane (CH&sub4;) — 1.25 percent LEL (lower explosive limit), the action point for LPG gas-detection in kitchens and gas appliance enclosures.
Carbon monoxide (CO) — 30 ppm 8-hour TWA. The basement car park CO control setpoint is typically 25 ppm action point with full extract at 50 ppm. CO is also a relevant indicator for gas appliance malfunction in any apartment with gas cooking.
R32 and R410A refrigerant — the dominant refrigerants in residential split-system and VRV plant. R32 has a lower GWP than R410A and is the current Australian default. Refrigerant leak detection in apartment plant rooms and in basement VRV outdoor unit areas is required where the refrigerant charge exceeds the threshold under AS/NZS ISO 5149.
Formaldehyde — 1 ppm STEL (short-term exposure limit). New-build off-gassing from MDF, particleboard and adhesives is a documented IEQ concern in the first 6 to 12 months of occupancy. Premium BTR specifications include 30-day flush-out at increased outdoor air rate before tenancy commencement to manage formaldehyde off-gassing.
VOC general — volatile organic compound exposure in new-build environments. Green Star Multi-Unit Residential credits low-VOC materials and adequate ventilation to manage off-gassing.
Respirable dust — 10 mg/m³ 8-hour TWA. Relevant to the construction phase and to retrofit and refurbishment work in occupied buildings.
Benzene — 1 ppm STEL. Basement car park exposure to petrol vapour, particularly at refuelling stations or fuel filler locations.
Nitrogen dioxide (NO&sub2;) — 5 ppm STEL. Gas cooking is a documented residential NO&sub2; source, and basement car park exhaust contains NO&sub2; from diesel and petrol engines.

SOU sole occupancy unit HVAC architecture

Sole occupancy units typically account for 60 to 75 percent of the gross floor area in a Class 2 high-rise. Designing SOU HVAC well is the single most important determinant of resident comfort, the single most reported source of complaints, and a major driver of operating energy.

Per-apartment plant configuration

The four mainstream SOU HVAC plant configurations in Australian Class 2 high-rise are:

Split-system reverse-cycle per habitable room. The dominant volume-builder configuration. Each bedroom and living room has its own wall-mounted or ceiling-cassette split unit with an outdoor condenser unit located on the apartment balcony or in a dedicated condenser bank on the building facade. Pros: low capex, simple maintenance, individual room control, refrigerant piping rather than chilled water through the building. Cons: condensers on balconies are an architectural and acoustic compromise, condensers on facade-mounted banks need detailed acoustic and aesthetic resolution, no central control of building energy.

Ducted reverse-cycle with concealed indoor unit. The dominant configuration in mid-premium volume apartments. A single concealed ceiling-cassette indoor unit serves the apartment via short flexible duct runs to each habitable room diffuser. Outdoor unit on balcony or facade bank. Pros: better aesthetics with concealed diffusers, single unit per apartment for easier maintenance. Cons: still requires per-apartment outdoor unit, slightly higher capex than splits, sound transmission via the duct path requires careful acoustic detailing.

VRV centralised refrigerant with per-apartment indoor unit. The dominant configuration in luxury and Build-to-Rent. A single central outdoor unit serves multiple apartments via a refrigerant piping network, with each apartment having its own indoor unit (cassette, ducted or wall-mounted). Pros: no condensers on apartment balconies, central control of building refrigerant inventory, efficient at part-load, common in BTR. Cons: higher capex, requires central plant deck space, refrigerant leak detection per AS/NZS ISO 5149, all apartments share the central plant for maintenance.

Four-pipe FCU with central chiller and boiler plant. The least common configuration in Australian residential — more common in serviced apartments and in adaptive-reuse heritage residential where refrigerant piping is impractical. Pros: simultaneous heating and cooling capability, no per-apartment refrigerant. Cons: highest capex, requires basement or rooftop chilled water and hot water plant, requires risers for both chilled water and hot water.

Whole-house mechanical ventilation (HRV / ERV)

Newer luxury apartments and most institutional BTR specifications include whole-house mechanical ventilation via a heat recovery ventilator (HRV) or energy recovery ventilator (ERV) per apartment, supplied from a small dedicated indoor unit in the apartment ceiling void or a building-level system serving multiple apartments through a tempered outdoor air riser. The HRV/ERV delivers tempered, filtered outdoor air directly to each apartment at the AS 1668.2 minimum or operator-overlay rate, and recovers heat or heat plus moisture from the apartment exhaust path. Energy savings versus open-window infiltration are 60 to 80 percent in winter and 30 to 50 percent in summer. The HRV/ERV is the dominant indoor environment quality differentiator in BTR projects and is the single largest sustainability story for a Class 2 apartment HVAC scheme.

SOU kitchen exhaust

AS 1668.2 sets the minimum kitchen exhaust for a sole occupancy unit at 40 L/s of mechanical wet-vapour exhaust OR an open balcony of compliant area as a deemed-to-satisfy alternative. The 40 L/s rate is the working basis for any internal kitchen or galley kitchen without compliant natural ventilation — which covers essentially every modern high-rise apartment because tower-form planning rarely delivers operable openings of the required free area at the cooktop position. The 40 L/s exhaust is achieved by a residential range hood compliant with the AS/NZS 1668.2 SOU range-hood provisions, ducted into a vertical riser that serves all apartments on the riser stack. Riser diameter steps up at floor groupings as the cumulative flow accumulates — typical mid-floor riser size is 300 to 400 mm diameter at 5 to 6 m/s velocity, rising to 500 to 700 mm at the rooftop. The riser discharges at roof via a smoke-rated extract fan with weatherproof termination. Premium and BTR operators commonly specify 60 to 90 L/s SOU kitchen exhaust to give a credible range-hood performance, to manage cooking odour in shared corridor and lift lobby returns, and to support the IEQ claim in marketing material.

The duct material in the SOU kitchen exhaust riser is the single most contested specification decision in Class 2 multi-residential HVAC. The volume-builder default is galvanised G275 throughout, which is durable and cost-effective in residential service. The premium-builder upgrade is 304L stainless from the range-hood transition to the roof, which is cleanable and supports a 10 to 15 year inspection cycle without internal coating breakdown. The BTR institutional specification is typically 304L stainless throughout because the BTR operator carries the 20 to 30 year operating cost of any duct degradation.

SOU bathroom exhaust

AS 1668.2 sets bathroom exhaust at 25 L/s for the water closet and 30 L/s for the shower, in continuous or intermittent service. Where a single bathroom contains both a water closet and a shower the combined exhaust is sized on the higher of the two values — 30 L/s — with humidity-boost capacity to 50 to 60 L/s during shower use, controlled by a humidistat or run-on timer. The exhaust path is a vertical riser serving multiple apartments per riser, with backdraft dampers at each apartment connection to prevent cross-apartment air migration. The riser discharges at roof via a constant-volume extract fan, with constant-volume regulators at each apartment connection to maintain flow regardless of stack effect or wind pressure on the rooftop discharge.

The bathroom exhaust riser is the single tightest mechanical service in a Class 2 high-rise — it is the primary path for cross-apartment odour and particulate transfer if the riser construction is not airtight at the apartment connection. The AS 1668.1 fire-rated construction of the riser is also critical because it crosses multiple SOU separating walls and floors, each of which requires an AS 1530.4 fire damper and an AS 4072 service penetration seal.

SOU laundry exhaust

SOU laundry exhaust is 25 L/s for the washer/dryer enclosure per AS 1668.2, with a separate compliant termination for any vented condenser or non-condensing dryer. The exhaust path is similar to the bathroom exhaust riser — vertical to roof via constant-volume extract fan, with backdraft dampers and constant-volume regulators at each apartment connection. Lint accumulation in the laundry riser is a documented fire risk and a maintenance burden, and the BTR institutional specification typically requires a dedicated low-velocity lint trap at each apartment connection and a roof-level lint collection box that can be cleaned without interrupting the riser service.

SOU general ventilation

SOU general ventilation under the Volume Two natural ventilation pathway (V_p) is supplied via openable window or compliant trickle vent. The window must have a compliant free area, the trickle vent (where used) must achieve the required flow at the design pressure differential, and the path between window or vent and the habitable room must be clear of obstruction. In premium and BTR apartments the natural ventilation path is supplemented or replaced by the HRV/ERV mechanical ventilation discussed above.

Acoustic specification — achieving NC-30 in apartment bedrooms

AS/NZS 2107 recommends NC-30 to NC-35 for apartment bedrooms. Achieving NC-30 reliably requires:

Indoor unit sound power selection — the split or ducted indoor unit must be sized for low-speed operation at room-peak sensible load, with manufacturer NC ratings at low speed of NC-27 or quieter
Lined supply duct — for ducted reverse-cycle, supply duct from indoor unit to bedroom diffuser is internally lined with mineral wool or fibre-free polymer lining, providing 8 to 12 dB attenuation per metre of duct length at the dominant frequencies
Low-velocity diffuser — supply diffusers selected for face velocity below 2 m/s and NC rating of NC-27 or quieter at design flow
Isolation hangers — the indoor unit is suspended on spring or rubber isolation hangers to break the structure-borne path from fan vibration to ceiling drywall
Bathroom exhaust isolation — the bathroom exhaust grille and riser must be acoustically separated from the bedroom by a closed bathroom door and lined transfer duct

Premium BTR specifications push apartment bedroom acoustic to NC-25 to NC-28, requiring additional lined duct length, inline attenuators downstream of the indoor unit and acoustic plenum boxes at each bedroom diffuser. The premium specification adds 8 to 12 percent to the SOU duct cost but is recognised in market take-up and lease premium for the BTR product.

For a deeper treatment of acoustic duct design see the SBKJ acoustic HVAC duct lining and attenuator guide.

Common area HVAC — corridor, lobby, lift lobby

Common areas in a Class 2 high-rise are the primary architectural expression of the building and the first impression for prospective residents, visitors and BTR prospects. The HVAC scheme has to deliver thermal comfort, manage smoke in fire mode, work invisibly within architectural feature ceilings, and avoid drafts at the entry door interface.

Apartment floor corridor

The apartment floor corridor serves as the evacuation route in fire mode and the primary circulation in normal occupancy. AS 1668.2 sets the corridor outdoor air rate at 10 L/s per person of occupancy load, which on a typical apartment corridor floor is the maximum occupant density at evacuation rather than steady-state occupancy. Practical design rate is therefore the higher of the AS 1668.2 calculation or the smoke spill rate from AS 1668.1, with the smoke spill rate typically dominating in any apartment floor with multiple SOUs sharing the corridor.

The corridor is typically supplied from a vertical fresh air riser via a small per-floor branch with a constant-volume regulator, and returned via the corridor air to the building return riser or to the floor's outdoor air relief. Corridor pressurisation is typically set slightly positive relative to the SOU interiors to prevent SOU exhaust migration into the corridor — this is achieved by the relative balance of supply rate, exhaust rate and door seal integrity.

Ground floor lobby

The ground floor lobby is the public face of the building. AS 1668.2 sets the lobby outdoor air rate at 10 L/s per person of design occupancy. The lobby supply scheme typically uses a dedicated AHU located in the basement or ground floor plant room, with supply diffusers integrated into the lobby ceiling architecture. Acoustic spec NC-35 with lined supply duct from AHU to lobby. Return air via low-level grilles to a return riser or via overhead transfer to the AHU return plenum. The lobby HVAC scheme must coordinate with the entry door air-curtain (where used) and with the AS 1668.1 lobby smoke management requirements where the lobby is more than a single-storey volume.

Lift lobby per floor

The lift lobby on each apartment floor is a small space (typically 10 to 25 m²) but is the primary interface between the corridor and the lift shaft. AS 1668.2 ventilation rate is 10 L/s per person of design occupancy. The lift lobby is typically integrated into the corridor supply and exhaust scheme with no separate AHU. The lift shaft itself is separately ventilated per AS 1735 lift standards, with shaft ventilation typically by a small dedicated fan at the top of the shaft. In fire mode the lift lobby is part of the corridor smoke spill zone and the lift shaft is part of the lift-shaft pressurisation or venting scheme.

Stair pressurisation system

AS 1668.1 requires fire-isolated stairs in any Class 2 building above two storeys to be pressurised in fire mode. The system maintains a minimum overpressure of approximately 50 Pa across the closed stair door, with airflow through any single open door of at least 1.0 m/s and an upper bound of 8.0 m/s (to keep stair-door opening force within the 110 N limit set by AS 1668.1). The pressurisation fan is a dedicated rooftop or basement smoke-rated unit, drawing outside air through a fire-rated duct to the stair shaft. Relief dampers at each floor or a single overpressure relief at the top of the shaft prevent the stair pressure from exceeding the 110 N door force limit. The fan and ductwork achieve a low leakage class — typically AS 4254 Class A or Class B — because leakage from the pressurised stair into the occupied corridor defeats the pressurisation calculation. Stair pressurisation ductwork is fabricated from galvanised G275 or higher with TDF flange joints, sealed gaskets and continuously welded penetrations.

Corridor smoke spill / smoke removal

AS 1668.1 requires corridor smoke spill or smoke clearance on every apartment floor — the system extracts smoke from the corridor in fire mode to keep the evacuation route clear. The smoke spill extract is typically a vertical riser drawing from a corridor exhaust grille on each floor, with a smoke-rated fan at the rooftop discharge. Total smoke spill rate is calculated per AS 1668.1 based on the floor area and the smoke layer height calculation, typically 1 to 4 air changes per hour of corridor volume. The ductwork is fire-rated to AS 1668.1 Class A leakage and the FRL matching the slab penetration rating (typically 90/90/90 or 120/120/120). Galvanised G275 to AS 4254 with TDF flange joints and continuously welded penetrations is the standard construction. The smoke spill fan is dual-purpose — in fire mode it runs at high speed for smoke removal, in normal mode it can be used for night-purge ventilation of the corridor.

For a deeper treatment of fire and smoke duct integration see the SBKJ fire and smoke damper HVAC duct integration guide.

Basement car park HVAC

The basement car park is typically the second-largest ductwork volume in a Class 2 high-rise after the SOU and corridor system. The HVAC scheme must deliver continuous ventilation for resident health (CO and pollutant control), smoke clearance in fire mode (basement fires are a major fire-safety scenario), EV charging zone ventilation (Li-ion battery thermal management), and connection to the rooftop or facade discharge stack.

General car park ventilation rate

AS 1668.2 sets the basement car park ventilation rate at 1 L/s per m² of floor area on a continuous basis, OR a demand-controlled jet-fan and CO-monitored system that achieves equivalent dilution at the design CO setpoint. For a typical 2,500 m² basement on a Class 2 high-rise that translates to 2,500 L/s of continuous extract with a matching supply path. The continuous extract scheme is the older convention; the demand-controlled jet-fan scheme is the current Australian practice and is what most new Class 2 buildings specify.

Demand-controlled jet-fan ventilation

Jet-fan ventilation uses induction-style jet fans located across the basement at strategic positions, drawing air from one end of the basement and pushing it to a single roof-discharged main extract fan. The induction effect of the jet fans amplifies the airflow without requiring full ductwork distribution — air moves through the open basement volume rather than through ducted branches. CO sensors per zone report to the BMS, and the main extract fan ramps from a continuous baseline (typically 10 to 30 percent of design extract rate) to full duty when CO exceeds the design setpoint. The action point setpoint is typically 25 ppm CO 8-hour TWA, with full extract at 50 ppm CO. The system saves 50 to 70 percent of basement ventilation energy versus continuous full-rate extract.

Smoke clearance in fire mode

In fire mode the basement ventilation system doubles as the smoke clearance system. The main extract fan is smoke-rated (typically 250°C/120 minutes per AS 1668.1) and the jet fans are smoke-rated. The CO and smoke detection signals trigger the BMS to switch the basement to fire mode, with the main extract running at full duty and the jet fans configured to drive smoke towards the extract point and away from the evacuation route. The smoke-rated extract ductwork is AS 4254 Class A or Class B leakage with TDF flange joints, galvanised G275 or higher, and FRL to AS 1530.4 matching the basement slab and wall ratings.

Rooftop discharge stack

The basement extract discharges at the rooftop via a stack at least 6 m above the highest occupiable opening within 15 m horizontally. Discharge velocity is typically 10 to 15 m/s to ensure dispersion above the building wake zone. The stack is acoustically attenuated where it passes near upper-floor SOUs or near the rooftop amenity, with line silencers and lined plenum boxes at the discharge point.

EV charging zone ventilation

EV charging zones in the basement require specific ventilation treatment because lithium-ion battery thermal runaway is a documented fire scenario. AS/NZS 5139 sets the safety requirements for electrical installations of battery systems, and the emerging NFPA 855 reference is increasingly cited by Australian designers for the additional ventilation and detection provisions specific to large Li-ion installations.

The recommended EV charging zone ventilation scheme is:

Dedicated zone exhaust at 6 to 10 ACH continuous
Spark-resistant fan motor and damper construction (the zone is treated as Zone 2 hazardous area under AS/NZS 60079 where battery thermal runaway is the design risk)
Early-warning smoke and battery off-gas detection (VESDA aspirating detection is the standard practice, with cross-zoning to the BMS fire alarm)
Isolation from the general basement ventilation path via fire dampers at the zone boundary, so a battery thermal runaway event does not load the general car park exhaust with battery off-gas (CO, HF, electrolyte vapour)
Roof discharge separate from the general car park extract or with a smoke damper at the junction to allow isolation

For a deeper treatment of EV charging and battery storage HVAC see the SBKJ EV charging and BESS HVAC duct guide.

Resident amenity HVAC — the BTR differentiator

Resident amenity is the primary product differentiation of Build-to-Rent over strata sell-down. A typical BTR amenity floor includes a gym, co-working office, cinema room, communal dining, pet wash, sometimes a swimming pool and spa, sometimes a music practice room and a maker space. Each amenity sub-space has its own HVAC sub-system with its own AS 1668.2 ventilation rate, its own AS/NZS 2107 acoustic target and its own architectural integration.

Gym and yoga studio

Gym ventilation rate per AS 1668.2 / ASHRAE 62.1 is the highest per-person rate of any normally occupied space — 20 cfm/person + 0.06 cfm/ft² (approximately 100 L/s/person + 0.3 L/s/m²) for general fitness, with yoga studio at the lower end (10 to 15 L/s/person) and high-intensity cardio at the upper end. Air change rate is typically 8 to 12 ACH for elevated odour and moisture management. Temperature setpoint is typically 20 to 22°C (versus 22 to 24°C in the rest of the building) to compensate for high metabolic rates. Filtration is MERV 13 with optional UV-C irradiation in the AHU to address equipment-related bioaerosols. Acoustic isolation is critical — gym free-weight drops generate impact noise that travels through the slab to apartments above, and the HVAC scheme should not exacerbate this with vibration-prone ductwork. Supply diffusers in flexible-mount frames isolated from the structural slab.

Locker rooms get 6 to 10 ACH exhaust, shower rooms get 8 to 12 ACH, both per AS 1668.2. The locker and shower exhaust paths use stainless steel for the wet portion to manage chlorine and humidity, transitioning to galvanised in the dry riser portion above ceiling.

Co-working office and study lounge

Co-working office space and student-accommodation study lounges follow the AS 1668.2 commercial office rate of 10 L/s per person of design occupancy. Acoustic spec NC-35 with lined supply duct. Demand-controlled CO2-based ventilation modulation is standard because co-working occupancy varies dramatically across the day and across the week. The supply diffuser layout coordinates with the work-station and meeting-pod layout, with quiet supply diffusers at each meeting pod and slot diffusers along the desking lines.

Cinema room

Cinema rooms in BTR amenity are typically 50 to 150 m² with raked seating for 20 to 50 viewers. AS 1668.2 outdoor air rate is 10 L/s per seat. Acoustic spec NC-25 to NC-30 to allow film soundtrack appreciation without HVAC interference — this is one of the tightest acoustic specs in the residential amenity space. Supply diffuser strategy is low-velocity slot or perforated tile to minimise diffuser noise, with lined supply duct and inline attenuators at the AHU outlet. Return path is via the corridor or via low-velocity lined return ducts to minimise return noise. Some premium BTR cinema rooms add a Dolby Atmos sound system that requires ceiling-mounted speakers integrated with the supply diffusers — the HVAC and AV coordination is a defining detail of the BTR cinema room.

Pet wash and dog spa

Pet wash facilities are an increasingly standard BTR amenity. Each pet wash bay is typically 4 to 8 m² with a stainless steel wash tub, fixed shower and grooming table. The HVAC scheme is 12 to 15 ACH continuous extract via stainless steel ductwork, with a humidity-boost rate to 20 ACH during active use, supplied with tempered makeup air to maintain comfortable bay temperature for pet and groomer. The exhaust path discharges separately to the building general exhaust to manage pet odour, hair and grooming chemical exposure.

Music practice and maker space

Music practice rooms (5 to 15 m² typically) need elevated ventilation due to small volume and continuous occupancy — 15 to 20 L/s per practitioner, with NC-25 to NC-30 acoustic to prevent practice noise from disturbing adjacent rooms and to prevent HVAC noise from disturbing the practitioner. Maker spaces (workshops with laser cutters, 3D printers, woodworking equipment) need higher exhaust rates to manage fumes and dust — 6 to 10 ACH baseline with local exhaust ventilation at fume-generating equipment, typically routed to a dedicated stainless or galvanised exhaust riser separate from the general building exhaust.

Communal dining and commercial kitchen

BTR communal dining rooms typically include a small commercial kitchen for resident catering events. The commercial kitchen exhaust follows NFPA 96 / AS 1668.2 commercial cooking provisions — 1.6 mm black steel grease duct, continuously welded liquid-tight seams, sloped 1:50 to the hood, access doors every 3.5 m, hood capture velocity 80 to 125 fpm. Replacement air at 70 to 90 percent of exhaust through a dedicated makeup air unit. See the SBKJ commercial kitchen exhaust HVAC duct guide for the full grease duct specification.

The communal dining area follows the AS 1668.2 dining rate of 10 to 15 L/s/person with NC-35 acoustic. The communal kitchen replacement air supplies the dining area with the balance keeping the kitchen at slight negative pressure to contain cooking odour.

Wine cellar and spirits storage

Some premium BTR amenity floors include a wine cellar or spirits storage area for residents. The HVAC scheme is a small dedicated cooling unit maintaining 12 to 14°C and 65 to 75 percent RH, with insulated supply and return ducts in galvanised steel. The wine cellar exhaust is a small dedicated path with humidity control to prevent excessive drying of corks. See the SBKJ wine cellar and spirits storage HVAC duct guide for the detailed specification.

Indoor pool plant

Where a BTR amenity floor includes a swimming pool, the pool hall HVAC follows the public aquatic centre specification — 316L stainless ductwork throughout the pool atmosphere, dedicated pool dehumidifier, slight negative pressure relative to surrounding spaces, and a vapour-tight pool envelope. See the SBKJ indoor pool and aquatic centre HVAC duct guide and the public aquatic centre HVAC duct guide for the detailed pool HVAC specification.

Mixed-use podium HVAC

The mixed-use podium of a Class 2 high-rise is typically two to three storeys at the base of the building, containing ground-floor retail (Class 6), level 1 office (Class 5), level 2 amenity or function space (Class 9b), and ground-floor lobby (Class 2 common area).

Class 6 podium retail

Ground-floor retail tenancies are typically cafes, restaurants, convenience stores, banks, fitness studios with retail trading, and small format shops. Each tenancy gets its own AHU, fresh air supply, exhaust path and BMS zone. AS 1668.2 retail rate is 10 L/s per person of design occupancy. Acoustic spec NC-40. The interface with the residential tower above is the most delicate part of the podium HVAC scheme — cooking odour, refuse smell, retail air exhaust must not migrate vertically into the apartment lobby or SOUs above. The base building delivers fresh air, exhaust, and gas (where required) to the tenant's lease line, and the tenant fitout connects to those services.

Cafes and restaurants in the podium require commercial kitchen exhaust to NFPA 96 / AS 1668.2 commercial cooking provisions. The grease duct is field-welded 1.6 mm black steel routed through a dedicated riser shaft to the rooftop discharge. The vertical kitchen exhaust riser must be coordinated at structural design because retrofitting a grease duct riser into a built structure is impractical. See the SBKJ cafe and quick service restaurant HVAC duct guide for the detail.

Class 5 podium office

Level 1 office tenancy in a mixed-use podium follows the SBKJ commercial office tower HVAC duct guide specification — AS 1668.2 office rate 10 L/s/person, NC-30 to NC-35 acoustic, MERV 13 filtration in the modern post-COVID specification, demand-controlled VAV with CO2 sensors, lined supply duct, and a dedicated office AHU. The interface with the residential tower above is via a dedicated services riser through the residential floors with full fire-compartmentation to AS 4072 and AS 1530.4.

Class 9b podium assembly

Level 2 amenity, function or assembly space follows the AS 1668.2 assembly rate of 10 L/s/person up to 15 L/s/person depending on the assembly type. Function spaces with operable partition walls require parallel HVAC zoning per partition section. Acoustic spec depends on use — NC-30 for cinema or performance, NC-35 for standard assembly.

Hotel-style serviced apartment lobby

Where the podium includes a serviced apartment operator (Quest, Mantra, Meriton Suites, etc.) the serviced apartment lobby follows the hotel lobby HVAC specification — see the SBKJ hotel and hospitality HVAC duct guide for the detail. AS 1668.2 lobby rate, NC-35 acoustic, dedicated lobby AHU with lined supply duct, and coordination with the serviced apartment brand engineering standard.

Student accommodation reception and study lounge

Purpose-built student accommodation reception and study lounge follow the AS 1668.2 reception and lounge rates — 10 L/s/person for the reception, 10 to 12.5 L/s/person for the study lounge, with NC-35 acoustic. Demand-controlled CO2-based modulation is standard for the study lounge because student occupancy varies dramatically across the academic year and across the day. The Scape and Iglu operator specifications typically push 12.5 L/s/person on the study lounge to support the wellbeing claims that drive lease take-up.

Retirement village HVAC

Retirement villages combine multiple NCC classifications on a single site — Class 2 independent living units, Class 9b community amenity (lounge, dining, library), and frequently Class 9c aged-care residential service in a co-located nursing home.

Independent living units

Retirement village independent living units are Class 2 SOUs and follow the standard apartment HVAC stack — AS 1668.2 SOU exhaust, residential range-hood ventilation, individual reverse-cycle split or VRV plant. The retirement-living overlay on a standard apartment specification includes:

Higher filtration (MERV 13 minimum) due to the higher prevalence of respiratory conditions in the over-55 resident demographic
Continuous low-rate bathroom exhaust regardless of occupancy — the bathroom exhaust runs continuously at 25 to 30 L/s rather than user-controlled, to manage humidity in interior bathrooms used 24/7 by residents with mobility limitations
Redundant reverse-cycle in the primary bedroom — impaired thermoregulation is common in the older demographic, and a single plant failure cannot leave the resident exposed to summer heat or winter cold
AS 1428 accessibility coordination — diffuser placement, grille placement and thermostat height must respect accessibility envelopes
Lower NC targets — NC-25 to NC-30 for bedrooms in premium retirement-living, recognising the age-related hearing-sensitivity concerns and the longer time spent in the apartment

Assisted living units

Assisted living units in a retirement village are typically Class 2 SOU in NCC classification but the operator specification pushes the HVAC harder on:

Continuous outdoor air supply via mechanical ventilation (HRV/ERV) rather than relying on window operation
Higher bathroom exhaust capacity (40 to 50 L/s) to manage the continence-aid moisture loads of residents with care needs
Dedicated humidity boost via humidistat and run-on timer
Acoustic targets at NC-25 for sleeping rooms
ASHRAE Standard 170 considerations from the healthcare HVAC framework, applicable in assisted-living contexts where care delivery may include infection-control protocols

Aged-care nursing home (Class 9c)

The aged-care nursing home (Class 9c) is a separate building classification with a separate HVAC stack. The SBKJ aged care, retirement and disability HVAC duct guide covers the Class 9c HVAC specification in detail — including the AS 1668.2 nursing home rates, the dementia-care thermoregulation provisions, the infection-control HVAC schemes for aged-care residents, and the anti-ligature ductwork detailing for memory-care wings.

Plant room and rooftop layout

The rooftop mechanical plant deck and the basement plant room are the two primary equipment locations on a Class 2 high-rise. The layout coordination across the project is critical because plant deck size, access and screening drive the architectural massing and the structural floor plate of the upper levels.

Rooftop mechanical plant

The rooftop plant deck typically holds:

SOU kitchen exhaust roof fan and discharge stack
SOU bathroom exhaust roof fan and discharge stack
SOU laundry exhaust roof fan and discharge stack
Corridor smoke spill extract fan and discharge stack
Stair pressurisation intake louvres
Basement extract discharge stack
EV charging zone exhaust stack (where applicable)
Refuse/waste chute exhaust stack
Generator room radiator and exhaust stack (where applicable)
Rooftop AHU serving any amenity floor or upper-level common area
Chilled water plant for any central chilled water system
VRV outdoor units (where the per-apartment VRV scheme uses central plant)
Communications and lift motor room ventilation outlets

Plant deck access for the 15 to 25 year plant replacement cycle is a structural design consideration — the deck must be sized for crane swap-out of major plant items at the end of operating life. Acoustic isolation from the rooftop amenity (where the building has a rooftop pool or BBQ deck) requires substantial line silencers, acoustic enclosures and discharge stack attenuation.

Basement plant rooms

The basement plant room typically holds:

Main building electrical switchroom
Domestic hot water plant (gas or electric heat pump)
Chilled water plant for any central chilled water system
Fire pump room with sprinkler tank and booster
Generator room with emergency power plant (where applicable)
Communications and IT room (NBN distribution frame, building telco infrastructure)
Concierge and admin office (where the building has a 24/7 concierge service)
Cold room / waste room for resident parcel storage and recycling
Pool plant room (where the building has an indoor pool)
Basement extract fan room (where the basement extract fan is basement-located rather than rooftop)

Plant room ventilation

AS 1668.2 plant room ventilation rate depends on the plant type. General electrical and mechanical plant rooms get 6 to 10 ACH continuous. Chiller plant rooms get the higher of 10 ACH continuous or the refrigerant leak dilution rate per AS/NZS ISO 5149. Hot water plant rooms with gas-fired boilers get combustion air at the gas-fired-equipment rate plus 6 ACH general ventilation. Generator rooms get radiator air at the engine cooling rate plus combustion air at the engine consumption rate plus 10 ACH general ventilation.

Refuse and waste room

Refuse and waste rooms in a Class 2 high-rise have a dedicated odour-control exhaust at 10 to 15 ACH continuous, routed through a vertical riser to a rooftop discharge stack. The exhaust path is separate from the general building exhaust to prevent odour migration. Carbon filtration on the exhaust is a premium specification for BTR and luxury apartments. The chute itself runs floor-to-floor and is integrated into the architectural shaft layout.

Generator room

Buildings with emergency power generation (large BTR developments, retirement villages, and any building with a designated life-safety load above the threshold) include a generator room containing a diesel or gas generator. The generator room HVAC scheme includes:

Combustion air intake sized for full engine load consumption
Radiator air intake and discharge sized for full engine cooling load
General ventilation at 10 ACH minimum to clear engine exhaust leakage
AS/NZS 60079 Zone 2 hazardous area classification for any fuel-tank vent area, with spark-resistant fan motor and damper construction
Acoustic isolation from surrounding spaces (generator runs at very high sound level during weekly test cycles)

Communications and IT room

Building IT and communications rooms (NBN, telco, BMS server) require continuous N+1 redundant cooling. Typical scheme is two small dedicated chilled water FCUs or DX cooling units, each sized for the full IT load, with BMS-monitored temperature and humidity. Temperature setpoint 22°C. The cooling system runs 24/7 independent of the general building HVAC.

Concierge and admin office

Concierge and admin offices are standard commercial office HVAC — AS 1668.2 office rate, NC-35 acoustic, lined supply duct, dedicated VAV or split-system unit. Operating hours match the building concierge service (typically 24/7 for premium BTR, business hours for strata).

Ductwork material schedule

Class 2 multi-residential duct material selection follows the space type, the air conditions, and the operator overlay. The standard specification for an Australian premium Class 2 high-rise is:

Galvanised G275 (Z275) for general HVAC

Galvanised steel sheet at G275 (Z275) zinc coating thickness is the workhorse of Class 2 HVAC — used for SOU supply and return (where ducted), corridor supply and return, lift lobby, ground floor lobby, basement car park general ventilation, residential amenity general HVAC, and the dry portion of plant room and rooftop discharge ductwork. G275 provides 30 to 50 year service life in conditioned indoor air. Lower zinc coatings are not recommended for Class 2 projects because of the long service life expectation and the cost of replacement in an occupied building.

Internally lined duct for acoustic supply

SOU supply duct upstream of bedroom diffusers, cinema room supply duct, music practice room supply duct, and any duct serving an NC-30 or quieter space gets internal acoustic lining. The lining is mineral wool or fibre-free polymer at 25 to 50 mm thickness with a perforated metal facing to prevent fibre erosion into the airstream. Lined duct provides 8 to 12 dB attenuation per metre of duct length at the dominant frequencies. The lined duct is fabricated on the SBAL-V auto duct line with the lining installed inline before transverse joint forming, which keeps the lining flush with the duct interior and eliminates the field-installation labour of retrofitting lining to a finished duct.

304L stainless

304L stainless is used in:

SOU kitchen exhaust riser (premium and BTR specification) from the range-hood transition to the rooftop discharge
BTR communal commercial kitchen non-grease exhaust (e.g. dishwash and pastry station)
BTR pet wash exhaust and supply
EV charging zone exhaust where chemistry and battery off-gas resistance matter
Pool plant exhaust transitions
Generator room exhaust transitions where exhaust gas contains corrosive components

316L stainless

316L stainless is used for any duct exposed to chlorinated pool atmosphere — supply, return and exhaust within the pool hall envelope. Premium BTR specifications use 316L throughout the pool zone with EPDM gaskets rated for chlorine exposure.

Black steel (welded) for grease exhaust

NFPA 96 / AS 1668.2 grease exhaust ducts in any commercial kitchen (podium cafe, BTR communal kitchen, podium restaurant) are 1.6 mm black carbon steel with continuously welded liquid-tight seams. Galvanised, stainless and aluminised steel are not acceptable for grease exhaust because they are not field-weldable to the required NFPA 96 standard. The grease duct is field-fabricated by the kitchen exhaust contractor — the auto duct line produces the make-up air and tempered supply ductwork, not grease ducts.

Spark-resistant configuration for EV charging and generator room

For EV charging zone and generator room ductwork — areas treated as Zone 2 hazardous area under AS/NZS 60079 — the ductwork construction follows the spark-resistant specification. Fan motors, damper actuators, fittings and any rotating element within the hazardous area is spark-resistant certified. The duct itself is typically 304L stainless with continuously welded seams in the hazardous zone, transitioning to galvanised outside the zone boundary.

Acoustic specification by space

The full acoustic specification matrix for a typical Australian premium Class 2 multi-residential project is summarised below. Premium and BTR brand overlays may tighten any individual line.

Penthouse bedroom (luxury and premium BTR) — NC-25
Premium apartment bedroom — NC-25 to NC-30
Standard apartment bedroom — NC-30 to NC-35
Apartment living and dining — NC-35
Apartment kitchen — NC-35 to NC-40
Apartment bathroom — NC-40
Apartment laundry — NC-40
Corridor (apartment floor) — NC-35 to NC-40
Lift lobby (apartment floor) — NC-35
Ground floor lobby — NC-35
Concierge and admin office — NC-35
Communal lounge and dining (BTR amenity) — NC-35
Cinema room (BTR amenity) — NC-25 to NC-30
Co-working office (BTR amenity) — NC-35
Gym and fitness (BTR amenity) — NC-40 to NC-45
Pet wash (BTR amenity) — NC-40
Music practice room (BTR amenity) — NC-25 to NC-30
Maker space (BTR amenity) — NC-40
Indoor pool (BTR amenity) — NC-35
Communal commercial kitchen (BTR amenity) — NC-45
Wine cellar (BTR amenity) — NC-30 to NC-35
Student accommodation room — NC-30 to NC-35
Student accommodation study lounge — NC-35
Retirement village ILU bedroom — NC-25 to NC-30 (premium) / NC-30 to NC-35 (mid)
Retirement village community lounge — NC-35
Podium retail (cafe, restaurant) — NC-40
Podium retail (general) — NC-40
Podium office — NC-30 to NC-35
Podium assembly (function space) — NC-30 to NC-35
Basement car park — NC-45 to NC-50
Plant rooms — NC-50 to NC-55 (operational, not normally occupied)

Construction phasing for Class 2 multi-residential

A typical 200-apartment Australian Class 2 high-rise has an 18 to 30 month construction programme on top of 12 to 24 months of design and planning approvals. The HVAC ductwork procurement and installation phasing typically follows this sequence:

Months 1 to 6 — Demolition, excavation, basement structure

Below-ground works including basement excavation, retaining walls, basement slab and lower-level columns. No ductwork installation yet but riser sleeve coordination and basement slab penetration sleeves are critical and irreversible if missed. Major HVAC riser shaft locations and slab penetration sleeves are locked in basement structural design.

Months 6 to 12 — Concrete structure to rooftop

Concrete structure up the tower including columns, slabs, lift cores, stair cores, and primary riser shafts. No major ductwork installation yet but riser sleeves through every slab and slab penetration sleeves for HVAC services are installed during slab pour. Late changes after slab pour are catastrophically expensive.

Months 8 to 14 — Major risers and basement plant

Major HVAC risers installed up the building including SOU kitchen exhaust riser, SOU bathroom exhaust riser, SOU laundry exhaust riser, corridor supply and return riser, stair pressurisation riser, smoke spill riser, basement extract riser and any chilled water riser. Basement plant room ductwork installation including electrical switchroom, hot water plant room, chilled water plant room, fire pump room, generator room. Total ductwork volume in this phase: approximately 20 to 30 percent of project total.

Months 12 to 18 — Podium fitout and ground floor lobby

Podium retail tenancy base building delivery to lease lines, podium office base building delivery to lease lines, ground floor lobby fitout including the entry lobby AHU and the concierge office, level 1 and 2 assembly amenity fitout. Total ductwork volume in this phase: approximately 15 to 20 percent of project total.

Months 14 to 26 — Residential floor rough-in

Apartment floor rough-in including SOU split or VRV indoor units, SOU range-hood roughed-in, SOU bathroom exhaust connected to riser, SOU laundry exhaust connected to riser, SOU general ventilation connected (HRV/ERV where specified), corridor supply and return branches connected from riser to floor distribution, lift lobby supply and return connected. Apartment floor work is the largest ductwork volume by linear metre but each individual apartment is small — pre-fabricated apartment duct kits are standard practice on volume builds above 100 apartments. Total ductwork volume in this phase: approximately 30 to 40 percent of project total.

Months 22 to 28 — Residential amenity and rooftop plant

Residential amenity floor fitout including gym, co-working, cinema, communal dining, pet wash, pool plant (where applicable). Rooftop plant deck installation including all rooftop fans, AHUs and discharge stacks. Total ductwork volume in this phase: approximately 10 to 15 percent of project total.

Months 26 to 30 — Pre-occupancy commissioning

Air balancing across the entire building — typically 6,000 to 12,000 individual measurement points on a 200-apartment Class 2 high-rise. Leakage testing on smoke management duct. Fire damper drop testing on every damper. NC measurement in 10 percent of apartments. Kitchen exhaust capture verification on every riser. AS 1668.1 stair pressurisation commissioning. AS 1668.1 corridor smoke spill commissioning. AS 1668.2 SOU and common-area ventilation commissioning. Basement car park demand-controlled commissioning. EV charging zone commissioning. BMS point validation against I/O list. Full commissioning manuals and as-built CAD packages — typically 1,500 to 3,000 pages on a 200-apartment Class 2 building.

Pre-occupancy commissioning is the most schedule-critical phase of a Class 2 project. Issues found here are 10 times cheaper to fix than post-occupancy, and pre-occupancy commissioning failures regularly delay occupancy certificate issue by 4 to 12 weeks at significant commercial cost — a 200-apartment BTR project running at the institutional yield expectation loses substantial revenue per week of delayed occupancy. The HVAC contractor's commissioning programme is therefore aligned with the building certifier's occupancy certificate timeline and with the BTR operator's pre-leasing calendar.

Class 2 retrofit and refurbishment market

The Australian Class 2 retrofit and refurbishment market is a substantial parallel source of HVAC ductwork demand. Existing 1980s, 1990s and 2000s apartment buildings are being retrofitted for:

Energy compliance (NCC Section J upgrade trigger on major refurbishment, NABERS Multi-Unit Residential rating improvement)
Acoustic upgrade (premium guest experience expectation, body corporate complaint resolution)
SOU kitchen and bathroom exhaust upgrade (older buildings often have undersized or non-compliant SOU exhaust)
Stair pressurisation upgrade (older buildings may have non-compliant or failed stair pressurisation systems)
Basement car park EV charging zone retrofit (every major retrofit since 2022 now incorporates an EV charging zone with the appropriate ventilation)
Apartment-level ducted reverse-cycle retrofit (replacing older through-wall window units or split systems with concealed ducted reverse-cycle)
Communal amenity addition (retrofitting BTR-style amenity into older strata apartment buildings to maintain market positioning)

Retrofit projects have unique HVAC challenges — existing structure constrains shaft and slab penetration locations, asbestos-era buildings (pre-1990) require careful demolition coordination, apartments remain in operation through phased shutdowns reducing daily working hours, and existing ductwork material may not be compatible with new specifications. The retrofit ductwork specification is identical to new build, but the procurement quantities are smaller per phase, the lead times are shorter, and the contractor margin pressure is higher because of programme complexity.

SBKJ machinery for Class 2 multi-residential projects

SBKJ supplies the duct manufacturing machinery used by HVAC fabricators serving Class 2 multi-residential projects across Australia and internationally. The machine selection below covers the full ductwork fabrication scope of a Class 2 high-rise, with the exception of NFPA 96 grease ducts (field-welded black steel, not produced on auto duct lines).

SBAL-V auto duct line — the workhorse

The SBAL-V auto duct line is the workhorse of Class 2 multi-residential HVAC fabrication. The SBAL-V is offered in models SBAL-V-1250J and SBAL-V-1500J, handles material thicknesses of 0.5 to 1.5 millimetres, with a maximum working width of 1,250 or 1,500 millimetres, at a forming speed of 16 metres per minute, with overall dimensions of 14,000 by 2,000 by 1,800 millimetres or 14,000 by 2,200 by 1,800 millimetres, requires 87 kilowatts, weighs approximately 16 tons, and runs on 380V 50Hz 3-phase. A single SBAL-V outputs approximately 60 m²/hour of rectangular galvanised duct with TDF transverse joint, and a 200-apartment Class 2 high-rise project typically requires 35,000 to 70,000 m² of galvanised rectangular duct supplied over an 18 to 30 month construction programme. One SBAL-V on single shift comfortably outputs the volume for one major Class 2 project at a time, with capacity headroom for parallel smaller projects.

The SBAL-V is the recommended workhorse for SOU supply and return ductwork, corridor supply and return, lift lobby, ground floor lobby, basement general ventilation, residential amenity general HVAC, and the dry portion of rooftop discharge ductwork. The line includes integrated TDF flange forming for AS 4254 Class A and Class B leakage, beading, and optional integral lining station for acoustic duct. See the SBAL-V product page and the full machines catalogue.

SBAL-II for entry-level apartment build

For volume builder apartment projects at entry-level price points, the SBAL-II auto duct line handles material thicknesses of 0.5 to 1.2 millimetres at the lower capex point compared to the SBAL-V. The SBAL-II is suitable for fabricators specialising in volume builder apartment projects (Meriton, mid-tier developer portfolios) where the gauge range is narrower and the throughput requirement is moderate. The SBAL-II runs at a lower capital cost than the SBAL-V but with reduced gauge headroom for smoke-rated and pressurised ductwork — a project mix that includes substantial smoke-management ductwork would step up to the SBAL-V.

SB-ZF1500 stitchwelder for stainless kitchen makeup air and pet wash

The SB-ZF1500 stitchwelder is critical to the Class 2 duct fabrication scope wherever stainless steel construction is specified. The machine handles material thicknesses of 0.8 to 3 millimetres, with a working length of 100 to 1,500 millimetres, covering diameters from Phi-150 to Phi-1500, with overall dimensions of 2,500 by 1,000 by 2,350 millimetres, running on 380V 50Hz 3-phase. Two applications dominate the Class 2 scope: the SOU kitchen exhaust riser welding for premium and BTR specifications using 304L stainless from the range-hood transition to the rooftop, and the BTR communal commercial kitchen makeup air ductwork where 304L stainless cleanability supports the food-safety inspection cycle. The stitchwelder also serves the pet wash exhaust ductwork, the pool plant transitions, and the EV charging zone stainless construction. SBKJ engineers commission the stitchwelder to the buyer's nominated 304L coil specification at FAT.

SBSF-1525 round-duct flanger for multi-storey return and smoke spill riser

The SBSF-1525 round-duct flanger forms connecting flanges on the ends of spiral duct sections and round fittings used throughout the multi-storey return riser and smoke spill riser scope. Material handled is black steel 0.5 to 2 millimetres or stainless steel 0.5 to 2.5 millimetres, flanging width 75 to 152 millimetres, maximum weight capacity 360 kilograms, requires 2.5 kilowatts, weighs approximately 520 kilograms, with overall dimensions of 2,200 by 1,100 by 1,240 millimetres, runs on 380V 50Hz 3-phase. The SBSF-1525 produces the flanged spiral round duct used for the corridor return riser, the SOU bathroom exhaust riser (where round duct construction is specified for the riser portion), the smoke spill riser, and the basement extract riser. Round duct is more efficient than rectangular for vertical riser applications because it has higher structural rigidity per unit weight and lower air-flow resistance for the same cross-sectional area.

SBFB-1500 spiral fitting forming line

For spiral duct fittings (elbows, reducers, branch tees, taps) on the round-duct portion of the Class 2 multi-residential project, the SBFB-1500 spiral fitting machine fabricates the corresponding fittings in matching diameter and material. Output diameters 80 millimetres to 1,500 millimetres; material galvanised, 304L stainless or 316L stainless to match the duct. The SBFB-1500 provides the fitting matching capability that pairs with the SBTF spiral tubeformer. Each riser branch at every apartment connection on every floor needs a precisely matched fitting — for a 30-storey building with 8 apartments per floor that is 240 branch fittings per riser, with multiple risers per building, totalling thousands of fittings on a typical Class 2 project.

SBTF-1602 spiral tubeformer for large basement car park extract main

The SBTF-1602 spiral tubeformer produces round galvanised, 304L stainless or 316L stainless duct in diameters from 80 to 1,600 millimetres for the large basement car park extract main, the rooftop discharge stack, and the corridor return riser. The SBTF-1602 handles galvanised material up to 2.0 millimetres thick and aluminium up to 3.0 millimetres. Round spiral duct is the preferred geometry for the basement car park extract main because the diameter (typically 800 to 1,200 mm on a major Class 2 building) is impractical in rectangular geometry, the structural rigidity of spiral construction is essential for the long horizontal runs across the basement ceiling, and the pressure drop is lower than equivalent rectangular at the same cross-sectional area.

Spark-resistant configuration for EV charging Li-ion zone and generator room

For ductwork serving the basement EV charging Li-ion zone and the generator room — areas treated as Zone 2 hazardous area under AS/NZS 60079 — the SBKJ machinery is supplied in spark-resistant configuration. The SBPC1500 plasma cutter is the most relevant machine because plate prep work in the hazardous area requires non-sparking tooling. The SBPC1500 prepares plate for plenum and large-section fabrication in material galvanised, 304L stainless, 316L stainless or carbon steel up to 12 millimetres thick. Plasma cutting accuracy plus or minus 0.5 millimetre; edge quality suitable for direct TIG or MIG welding without secondary machining. The spark-resistant configuration is critical for plate prep work in the EV charging zone ductwork and the generator room exhaust ductwork — these are Zone 2 hazardous areas where uncontrolled sparking is a documented ignition source. SBKJ supplies the SBPC1500 with the spark-resistant tooling kit for hazardous area fabrication.

SBPC1500 plasma cutter for plate prep

The SBPC1500 plasma cutter is the general-purpose plate-preparation machine for any plenum, custom fitting or large-section duct on the Class 2 scope. Material galvanised, 304L stainless, 316L stainless or carbon steel up to 12 millimetres thick. Plasma cutting accuracy plus or minus 0.5 millimetre. The SBPC1500 prepares the AHU plenum housings, the rooftop fan housing plate, the basement extract plenum, and any custom transition fittings between rectangular and round duct on the riser system.

SBLR-600 longitudinal seam welder

For in-shop seam welding on rolled-and-formed duct sections, the SBLR-600 longitudinal seam welder produces continuous TIG seams on sections up to 6 metres long. Output suitable for the largest plenum sections on a Class 2 project — AHU plenums, basement extract plenum, rooftop fan housing plenum, smoke spill riser plenum, and any large duct section requiring continuous welded construction for AS 1668.1 fire and smoke management compliance. The longitudinal seam welder is essential for the Class 2 scope where continuously welded seams replace stitch-welded or lock-seam construction in smoke-rated or pressurised ductwork zones.

The combined SBKJ machinery footprint for a Class 2 high-rise fabricator

The combined SBKJ machinery footprint for a major Australian Class 2 multi-residential HVAC fabricator is typically: one SBAL-V galvanised line for rectangular duct (or two for high-volume fabricators serving multiple projects in parallel), optionally one SBAL-II for entry-level project mix, one SBTF-1602 spiral tubeformer with multi-material capability (galvanised, 304L stainless, 316L stainless), one SBFB-1500 spiral fitting machine, one SBSF-1525 round flanger, one SB-ZF1500 stitchwelder for stainless and welded-seam stations, one SBPC1500 plasma cutter (with spark-resistant tooling for EV charging and generator room work), and one SBLR-600 longitudinal seam welder for plenum and rooftop fan housing fabrication. The combined output capacity supports a 3,000 to 8,000 square metres per month duct fabrication rate, sufficient for the largest single Class 2 high-rise project or two to three medium-sized projects in parallel.

How SBKJ supports Class 2 project teams

SBKJ Group works directly with HVAC fabricators serving the Australian Class 2 multi-residential sector, including fabricators supplying the major BTR operator portfolios (Mirvac LIV, Greystar, Hines, Cbus Element), the major apartment developer portfolios (Meriton, Mirvac strata, Lendlease, Multiplex, Crown Group, TOGA), the major PBSA operator portfolios (Scape, Iglu, UniLodge), and the major retirement village operator portfolios (Aveo, Levande, IRT). The SBKJ engineering team supports project teams in three ways:

Duct line sizing — given a Class 2 project programme (apartment count, m² of duct, construction duration), we size the SBAL-V or SBAL-II configuration that matches the throughput requirement with sensible utilisation. A 200-apartment Class 2 high-rise needs one SBAL-V on single shift; a 600-apartment BTR development needs two SBAL-V on single shift or one on double shift.
Material specification matching — our standard auto duct line handles 0.5 to 1.5 mm galvanised G275. For 304L stainless SOU kitchen exhaust risers and BTR amenity stainless work we configure tooling for stainless stock; for 316L stainless pool and spa duct we configure for 316L; for 1.6 mm black steel NFPA 96 grease ducts in podium commercial kitchens, we point to specialist welded-pipe suppliers because grease ducts are not auto-line products.
Acoustic duct optimisation — we specify the inline lining station for fabricators serving the premium and BTR segment where lined duct volume justifies the in-line lining capability versus field lining. Pre-fabricated apartment duct kits (where multiple ducts and fittings are pre-assembled for installation at the apartment floor) speed apartment-floor fitout dramatically and are recommended for any volume builder running more than 100 apartments per project.

SBKJ Group is based in Box Hill North, Victoria, and has supplied HVAC duct machinery to fabricators operating across the Australian eastern seaboard (NSW, Victoria, Queensland), Western Australia, and South Australia. After-sales engineering is provided in English from the Melbourne office with on-site visit capability for major projects. The Box Hill North office is 25 minutes from the Melbourne CBD by car and within easy travel of every major Class 2 high-rise project in metropolitan Melbourne. See the SBKJ Australia regional page for the local presence and case studies, and the SBKJ Australia HVAC duct fabrication setup guide 2026 for the local fabricator landscape.

Common Class 2 multi-residential HVAC specification mistakes

Mistake 1 — Undersized SOU kitchen exhaust riser

The most common SOU specification mistake. AS 1668.2 sets the minimum at 40 L/s per apartment, but the riser must be sized for the cumulative diversified flow across all apartments on the riser. Sizing the riser at the per-apartment minimum without diversity factor results in cumulative undersizing — the lower apartments get adequate exhaust, the upper apartments get progressively less as the riser capacity is consumed by the apartments below. The fix is to size the riser at the diversified design rate per AS 1668.2 with an appropriate occupancy diversity factor (typically 0.5 to 0.7 for kitchen exhaust on a residential riser), or to specify the riser at the cumulative full-rate flow for absolute confidence.

Mistake 2 — Galvanised SOU kitchen exhaust riser in BTR specification

BTR operators retain the asset for 20 to 30 years and pay every operating cost. A galvanised SOU kitchen exhaust riser will accumulate grease deposit and zinc corrosion over the operating life, requiring intrusive cleaning every 5 to 7 years and replacement at 15 to 25 years. The 304L stainless premium at procurement is approximately 3 to 4 times the galvanised cost; the avoided cleaning intrusion (closing apartments for riser access) and avoided replacement loss is two orders of magnitude larger.

Mistake 3 — Continuous-extract basement ventilation without demand-controlled commissioning

The older convention of continuous full-rate basement extract at 1 L/s per m² is energy-wasteful and is no longer the practical specification for new Class 2 buildings. Modern AS 1668.2 compliance and NABERS Multi-Unit Residential rating both favour demand-controlled jet-fan ventilation with CO and CO2 sensors. The mistake is specifying the demand-controlled scheme but failing to commission the CO setpoint, the ramp logic and the BMS interaction at handover — the system runs as a fixed-rate fan ignoring the sensors, defeating the energy saving. Commissioning the demand-controlled ramp logic in the building under realistic occupancy conditions is essential.

Mistake 4 — Stair pressurisation door force exceeding 110 N

AS 1668.1 caps the maximum stair door opening force at 110 N. Over-pressurised stair systems with overpressure relief mis-set, undersized relief paths, or wind-loaded windward facade orientations exceed the 110 N limit and the stair door cannot be opened by an evacuating occupant. This is a documented failure mode in pre-commissioning inspections and is the leading cause of occupancy certificate delays on Class 2 high-rise projects. The fix is to commission the pressurisation system under realistic conditions including wind-load simulation and to verify the door force at the most-loaded door under design conditions.

Mistake 5 — SOU bathroom exhaust riser leakage to corridor

The SOU bathroom exhaust riser is the primary path for cross-apartment odour and particulate transfer if construction is not airtight. Leakage from one apartment's exhaust into another apartment's bathroom occurs when the riser ductwork is not sealed to AS 4254 Class B or better, when the backdraft damper at each apartment connection is missing or failed, or when the riser fan-off condition allows stack-effect-driven reverse flow. The fix is to specify AS 4254 Class B leakage minimum for SOU bathroom risers, backdraft damper at every apartment connection, and constant-volume regulators to maintain flow against wind and stack pressure.

Mistake 6 — Missing EV charging zone isolation

Newer Class 2 retrofit and new-build projects routinely include a basement EV charging zone but fail to provide the isolation from the general basement ventilation path. Without isolation, a lithium-ion thermal runaway event releases CO, HF and electrolyte vapour into the general basement extract, contaminating the smoke clearance path that the evacuating residents need. The fix is to specify smoke and fire damper isolation at the EV charging zone boundary, with the zone exhaust routed to a dedicated rooftop stack separate from the general basement extract.

Mistake 7 — Inadequate corridor smoke spill commissioning

AS 1668.1 corridor smoke spill is a fire-mode-only system that is easy to install but difficult to verify in operation. The mistake is to commission only at zero wind condition and to fail to verify smoke spill performance under realistic conditions including adjacent fire compartment depressurisation, stair pressurisation interaction, and lift shaft pressure differentials. The fix is to specify the AS 1668.1 commissioning protocol including hot-smoke testing or equivalent verification, with smoke spill performance documented under the full fire-mode operating envelope.

Mistake 8 — Refuse chute exhaust connected to general SOU exhaust path

The refuse chute on a Class 2 high-rise generates substantial odour particularly in summer. Connecting the refuse chute exhaust to the general SOU bathroom exhaust riser or to the corridor exhaust contaminates the residential exhaust path with refuse odour, generating immediate post-occupancy complaints. The fix is a dedicated refuse chute exhaust riser to a rooftop discharge stack separate from the SOU exhaust paths, with carbon filtration on the discharge for premium BTR specifications.

Frequently asked questions

What ventilation rate does AS 1668.2 require for a Class 2 sole-occupancy unit kitchen?

AS 1668.2 sets the minimum kitchen exhaust for a sole-occupancy unit at 40 L/s of mechanical wet-vapour exhaust, OR an open balcony/openable window of compliant area as a deemed-to-satisfy alternative. The 40 L/s rate is the working basis for any internal kitchen or galley kitchen in apartments without compliant natural ventilation — which covers most modern high-rise Class 2 stock because tower-form planning rarely delivers operable openings of the required free area at the cooktop position. Premium and Build-to-Rent operators commonly specify 60 to 90 L/s to give a credible range-hood performance and to manage cooking odour in shared corridor and lift lobby returns.

What exhaust rates apply to apartment bathrooms and laundries under AS 1668.2?

AS 1668.2 sets 25 L/s for a Class 2 SOU water closet and 30 L/s for a shower room. Where a single bathroom contains both, exhaust is sized on the higher of the two values (30 L/s) with humidity-boost to 50 to 60 L/s during shower use. SOU laundry exhaust is 25 L/s for the washer/dryer enclosure, with a separate compliant termination for any vented dryer. Premium BTR apartments often double the AS 1668.2 minimum to manage humidity in interior bathrooms with no external wall.

How does stair pressurisation work in an Australian Class 2 high-rise?

AS 1668.1 requires fire-isolated stairs in any Class 2 building above two storeys to be pressurised in fire mode. The system maintains approximately 50 Pa overpressure across the closed stair door, with airflow through any open door of 1.0 m/s minimum and 8.0 m/s maximum to keep stair-door opening force within the AS 1668.1 limit of 110 N. The pressurisation fan is a rooftop or basement smoke-rated unit drawing outside air through fire-rated duct to the stair shaft. Ductwork is AS 4254 Class A or Class B leakage because riser leakage defeats the pressurisation calculation.

What duct material should apartment developers specify for SOU kitchen and bathroom risers?

Galvanised G275 to AS 4254 is the default for SOU bathroom risers, laundry risers, and the dry portion of kitchen risers above the range-hood transition. For the wet, grease-bearing section directly downstream of the range hood the cleanest practice is 304L stainless or aluminised steel. BTR and premium serviced-apartment operators frequently specify 304L throughout the kitchen riser for cleanability and the 10-year inspection cycle. For BTR communal commercial kitchens and any cafe in the podium, NFPA 96 / AS 1668.2 commercial cooking applies — 1.6 mm black steel, fully welded grease duct.

How does basement car park ventilation work for a Class 2 building under AS 1668.2?

AS 1668.2 sets basement car park ventilation at 1 L/s per m² continuous or equivalent demand-controlled jet-fan and CO-monitored system. For a 2,500 m² basement that is 2,500 L/s of continuous extract. Demand-controlled jet-fan systems are the current practice — jet fans across the basement, CO sensors per zone reporting to the BMS, and a roof-discharged main extract that ramps from baseline to full duty at the design CO setpoint (typically 25 ppm 8-hour TWA action point). The system doubles as the smoke-clearance system in fire mode with smoke-rated fans and AS 4254 Class A or Class B ductwork.

What HVAC differences apply between BTR and conventional strata apartment buildings?

Four defining differences. First, single-ownership operating economics — the BTR operator retains the asset and pays the energy bill, so capex on heat recovery, MERV 13, demand-controlled basement, low-leakage duct and BMS metering returns directly. Second, substantial communal amenity — gym, co-working, cinema, pet wash, dining, sometimes pool — each its own AS 1668.2 sub-system. Third, tenancy turnover drives cleanable, durable, low-maintenance duct specification. Fourth, the PCA BTR Industry Standards provide a voluntary specification overlay above NCC minimum on IEQ — most institutional BTR projects specify to PCA BTR on top of NCC.

What ventilation rate applies to student accommodation rooms?

Purpose-built student accommodation operates under NCC Class 3 in most building forms, with some new projects enrolled as Class 2 SOU clusters. AS 1668.2 outdoor-air rate for a sleeping room in Class 3 is 7.5 L/s per occupant. Premium operators (Scape, Iglu, UniLodge, Yugo) commonly specify 10 to 12.5 L/s per room to manage CO2 and the wellbeing claims that drive lease take-up. Communal study lounges and dining at the AS 1668.2 commercial rates with demand-controlled CO2-based modulation.

What HVAC requirements apply to retirement village independent living versus assisted living?

Retirement village ILUs are Class 2 SOUs — standard apartment HVAC stack with AS 1668.2 SOU exhaust, residential range-hood and individual reverse-cycle. Assisted-living units remain Class 2 but the operator specification pushes harder on MERV 13 filtration, continuous low-rate bathroom exhaust, redundant reverse-cycle for thermoregulation, and NC-30 acoustic for sleeping rooms. Aged-care nursing homes (Class 9c) are a separate classification with a separate HVAC stack — see the aged care, retirement and disability HVAC duct guide.

What duct standards apply to apartment HVAC projects in Australia?

AS 4254.1 (rectangular) and AS 4254.2 (round) for general HVAC, AS 1668.1 for fire and smoke duct (stair pressurisation, corridor smoke spill, basement smoke clearance), AS 1668.2 for ventilation, AS 1530.4 for fire-rated penetrations, AS 4072.1 and AS 4072.3 for SOU separating element penetrations, AS 1851 for fire damper maintenance, AS 2107 for acoustic, NCC Section J for energy. NABERS Multi-Unit Residential and Green Star Multi-Unit Residential overlay the regulatory minimum.

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