Residential HVAC Duct Guide — Apartments, Townhouses, NCC 7-Star NatHERS, Mirvac, Meriton, Electrification

Why residential HVAC is its own discipline

Residential HVAC is the cousin every commercial mechanical engineer thinks they understand and almost always under-estimates. The systems are smaller — a typical 200 m² Australian detached house runs an 8–12 kW ducted reverse-cycle split, an apartment a 4–6 kW indoor unit. The duct runs are shorter. The fan power is a fraction of a hospital AHU. The standards reference the same AS 1668.2 and AS 4254 you see on commercial work. Yet residential design has a tighter set of binding constraints than almost any commercial typology, and the ductwork that satisfies them looks very little like the office-tower duct you may have grown up with.

The first constraint is cost. A residential duct package on a volume builder home is sold to an end customer who is also paying for the kitchen, the carpet, the deck and the landscaping out of the same fixed budget. Mechanical sub-contractor margins are wafer-thin and the consequence is the dominance of flexible insulated ducting — fast to install, cheap, and durable enough to outlast the new-home defect-liability period if the installer takes any care with the supports and connections. On a multi-residential apartment job the per-unit duct allowance is a similarly hard line in a developer's feasibility model. The mechanical engineer who writes a beautiful rigid-duct specification without first checking the developer's per-key budget is writing a value-engineering brief for the head contractor.

The second constraint is occupant control. A typical office tenant accepts that the building HVAC is set somewhere outside their authority — somebody else decided 22.5 °C ± 1 °C is the comfort range and the controls are inaccessible. Residential occupants expect the opposite. Bedroom A is set to 19 °C for sleep, bedroom B to 21 °C, the living room to 23 °C and the bathroom to whatever the radiant towel rail produces. Single-system ducted reverse-cycle with a single thermostat in the hallway cannot deliver this. Zoning — motorised dampers in branch ducts driving from individual room thermostats — is now standard on premium ducted residential systems and increasingly common on volume builder homes. Branch ductwork must accommodate the zoning hardware, leakage class must be tight enough that closed dampers actually shut off airflow, and the fan must be variable-speed (ECM motor) to track partial-zone load.

The third constraint is night-time acoustics. Bedrooms are designed to NC-25 to NC-30 under AS/NZS 2107:2016 because residents sleep in them — the office NC-35 to NC-40 design point is not an option. Achieving NC-25 to NC-30 with the indoor unit located in the same ceiling void as the bedroom means duct face velocities at the ceiling diffuser must drop to 1.5–2.5 m/s, every fitting must be selected for low regenerated noise, and acoustic lining or attenuators are routinely required on the supply trunk. The cheap volume-builder approach of running a flexible branch from indoor unit straight to the bedroom diffuser will fail an acoustic test on a premium project; rigid duct with acoustic lining is the only path to NC-25 in a master bedroom directly below a noisy fan coil.

The fourth constraint is mixed-mode operation. Australian residential is overwhelmingly ducted reverse-cycle — the same system heats in winter and cools in summer. Ductwork sized for one season can be uncomfortable in the other. Heat pump supply temperatures (35–50 °C in heating, 12–16 °C in cooling) are gentler than a gas furnace (60–70 °C heating) — the heating mode needs more airflow per kW to deliver equivalent room comfort, which means duct sizing is typically driven by heating mode in southern Australian climates and cooling mode in tropical markets like Brisbane and Darwin. Designers who size on cooling alone end up with a system that struggles to heat the bedrooms on a Melbourne winter morning.

The fifth constraint is durability versus first cost. A residential duct system is supposed to last the life of the building — 50+ years for an apartment, 30–50 years for a quality detached house. Flexible insulated ducting in an Australian roof void degrades over 10–15 years (UV embrittlement of the outer foil through the ceiling penetrations is the most common failure mode, followed by mechanical damage from electricians, plumbers and roof access). Replacing a flexible duct system in an apartment ceiling void with the unit occupied is a major operation. Rigid galvanised duct lasts 30+ years, is cleanable to AS/NZS 3666, and is the right specification on any project where the long-term operating cost is in the developer's interest — Build-to-Rent above all, but increasingly premium owner-occupier apartments and any villa where the buyer expects the HVAC to outlast their tenure.

This guide walks through residential HVAC ductwork from these five constraints down. We cover the eight residential building types from detached house to high-rise apartment, the binding NCC 2022 standards, the Australian developer landscape, ductwork architecture for each typology, ventilation and exhaust, fire and smoke control, acoustics, materials and the production-line economics that determine which fabricator can quote your project. References to specific Australian developers are based on publicly available information about their housing portfolios — no claim is made of any commercial relationship except where SBKJ has an active customer relationship with a project sub-contractor.

Residential building types — eight categories, eight HVAC patterns

Residential is not one market. It is a layered set of building typologies, each with its own NCC class, its own typical HVAC architecture, its own developer cohort and its own ductwork rules of thumb. The eight categories below cover roughly 95 percent of the Australian residential pipeline.

1. Detached single-family house (Class 1a)

The owner-occupier suburban detached house is the largest single segment by volume — roughly 100,000 new starts per year nationally in normal market conditions. NCC Volume 2 (the Housing Provisions) governs construction. NatHERS 7-star is the minimum thermal performance under NCC 2022 with a separate whole-of-home energy use cap. HVAC is overwhelmingly ducted reverse-cycle (8–12 kW capacity) with the indoor unit in the ceiling void, supply ducts to each room and a single central return grille. Volume builder market uses flexible insulated branches throughout; premium custom homes increasingly specify rigid galvanised trunks with flexible drops at diffusers. Bathroom and kitchen exhaust direct to outside via short ducts and roof or wall caps.

Major detached-home builders include Metricon, Mirvac (House & Land), Stockland, Henley, Burbank, Simonds, Porter Davis (succeeded by Nostra), G.J. Gardner, Hotondo and McDonald Jones. Mechanical sub-contractor selection is generally on a project-rate panel basis with the head contractor — first-fix HVAC is bundled into framing and plumbing trade packages.

2. Townhouse and duplex (Class 1a)

Townhouses and duplexes share an external party wall with the neighbouring dwelling but are otherwise classified Class 1a — same NCC Volume 2, same NatHERS 7-star, same HVAC architecture as detached. The added requirement is the party wall fire compartmentation: any duct crossing the wall (typically only bathroom or kitchen exhaust if architecture forces it) must have a fire damper to AS 1530.4 with FRL matching the wall — typically 60/60/60 minutes. Ducted reverse-cycle indoor units must not share a ceiling cavity across the party wall.

Townhouse delivery is dominated by Stockland (the largest townhouse delivery in Australia), Mirvac, Frasers, Lendlease and the major detached builders extending into smaller-lot product. Duct specifications mirror detached but with closer attention to inter-tenancy acoustic separation per NCC Volume 2 part 10.7 (formerly H1.7) — Rw + Ctr ≥ 50 dB across the party wall.

3. Low-rise apartment (Class 2, 3–4 storeys)

Low-rise apartment buildings — typically 12–48 units across 3–4 storeys with no lift required at the lower end — fall under NCC Volume 1 Class 2. HVAC is most commonly individual split systems per apartment (no shared duct) with separate bathroom and kitchen exhaust risers. Ducted reverse-cycle is offered as a premium upgrade in some schemes. Common areas (corridors, lobby, basement parking) have their own ventilation per AS 1668.2.

Low-rise developer cohort is broad: Mirvac, Lendlease, Frasers, Stockland, plus a long tail of regional and boutique developers. Per-apartment HVAC specification is generally tighter than detached because NCC Volume 1 imposes inter-tenancy acoustic and fire requirements that detached does not.

4. High-rise apartment (Class 2, 5+ storeys)

High-rise apartment towers (5+ storeys, lift-required, plant rooms, central services) are the dominant new-build typology in Sydney, Melbourne, Brisbane and Gold Coast. NCC Volume 1 Class 2 with significantly more onerous fire, smoke and acoustic requirements. HVAC architecture varies:

• Individual split per apartment — most common in cost-driven developments. No shared HVAC duct between apartments. Each apartment has its own outdoor unit on a balcony or rooftop plinth, indoor unit in a ceiling cavity or wall-mounted, refrigerant pipe between the two. Bathroom and kitchen exhaust to vertical risers.
• Ducted reverse-cycle per apartment — premium developments. Each apartment has its own indoor unit in a ceiling void with full duct distribution to all rooms. Galvanised trunks with flexible drops are increasingly standard at the top end.
• Central plant with FCUs — high-end and Build-to-Rent. Central chiller and boiler (or heat pump) plant on rooftop or basement, two-pipe or four-pipe water distribution to fan coil units in each apartment. Single point of system maintenance, lower per-apartment electrical load, but tenant comfort depends on plant operating regime.
• Dedicated outdoor air system (DOAS) for ventilation — separate ventilation system delivers tempered fresh air to each apartment, with sensible cooling provided by individual splits or FCUs. The DOAS approach decouples ventilation from cooling and allows each apartment to control its own temperature without affecting fresh air supply.

High-rise developer cohort is concentrated: Meriton (the largest single apartment developer in Australia, also operator of Meriton Suites serviced apartments), Mirvac, Lendlease, Frasers, Greenland Group, Crown Group, Aria Property Group, Greaves Group. Construction is typically delivered by Multiplex, Hutchinson Builders, Built, Roberts Co or Lendlease Building. Each combination has its own established mechanical specification template and tier-1 sub-contractor list.

5. Serviced apartment (Class 3 or hybrid)

Serviced apartments — Meriton Suites, Quest, Adina, Oaks, Mantra and similar — sit in a hybrid space between hotel and apartment. NCC classification depends on operation: short-stay only is Class 3 (hotel-equivalent), long-stay or strata-titled with hotel management is typically Class 2 with operational overlay. HVAC architecture mirrors hotels — ducted reverse-cycle or FCU per unit, central DOAS for corridor and ventilation, rigid galvanised duct construction throughout — with the additional requirement of self-contained kitchenettes that demand exhaust per AS 1668.2 domestic kitchen rates.

Cross-reference our hotel and hospitality HVAC duct guide for detailed specifications applicable to serviced apartments.

6. Retirement village and aged care (Class 1b, 2 or 3 hybrid)

Retirement villages typically combine independent living units (ILUs, classified Class 1a or 2 depending on form), assisted living and high-care wings (Class 9c residential care). HVAC for ILUs mirrors apartment specification — individual splits or ducted reverse-cycle per unit. The high-care wing is closer to a healthcare facility — central HVAC, AHRAE 170 lite ventilation requirements, infection control duct surfaces, dedicated dirty-air exhaust.

Major retirement and aged care developers/operators include Stockland (largest residential retirement living owner in Australia), Lendlease, Bolton Clarke, Allity, Bupa, Estia, Regis and Aveo. Mechanical specifications vary widely between independent living (residential-grade) and high-care (commercial healthcare-grade).

7. Student accommodation (Class 3)

Purpose-built student accommodation (PBSA) — UniLodge, Scape, Iglu, UniGroup, Y Suites, Atira and similar — is classified Class 3. HVAC architecture is similar to hotel guest room (individual ducted FCU or split per unit, central DOAS for corridors) but with the added complexity of shared kitchen and bathroom configurations in some designs. Per-room exhaust and supply must accommodate higher occupancy density than typical residential.

8. Social and affordable housing

Social and affordable housing — delivered by state housing authorities (Homes NSW, Homes Victoria, QLD Department of Housing), community housing providers and increasingly Build-to-Rent operators with affordable component — is currently the fastest-growing residential capex segment. The federal Housing Australia Future Fund (HAFF) commits AUD 10 billion to social and affordable housing delivery, supplemented by state programmes. HVAC specifications target NCC minimums — NCC 2022 7-star NatHERS, ducted reverse-cycle or split per dwelling, AS 1668.2 minimum ventilation. Build quality and HVAC commissioning have historically been variable in this segment; recent reforms (NSW Building Commissioner, similar bodies in other states) aim to lift standards.

The Australian residential context — housing shortage, NCC 2022, electrification

Three structural forces are reshaping Australian residential HVAC ductwork specification right now. Any mechanical engineer or duct fabricator quoting residential work in 2026 needs to understand all three.

The housing shortage and capex pipeline

Australia is delivering far fewer homes than population growth requires. The federal government's National Housing Accord targets 1.2 million new homes over five years from 1 July 2024 — a 240,000 per year run rate that the construction industry has not achieved in any single year since the 1970s. The shortfall is concentrated in metropolitan apartments and townhouses, the typologies most relevant to HVAC duct fabricators. Capital programmes responding to the shortage include:

• Housing Australia Future Fund (HAFF) — AUD 10 billion federal investment vehicle delivering social and affordable housing through community housing providers and state programmes.
• State social housing programmes — Homes NSW, Homes Victoria, QLD Department of Housing each running multi-billion AUD construction programmes.
• Build-to-Rent (BtR) — emerging institutional asset class with operators including Greystar, Mirvac, Lendlease, Frasers Property and several international owners. BtR developments specify higher-spec HVAC than typical owner-occupier apartments because the operator owns the operating cost.
• Private apartment delivery — Meriton, Mirvac, Lendlease, Stockland, Frasers, Greenland Group, Crown Group, Aria Property Group continue to deliver private-sale apartments to investor and owner-occupier markets.

For an HVAC duct fabricator the implication is straightforward — the residential pipeline over 2026–2030 is the single largest opportunity in Australian construction, and the specifications are tightening. The volume-builder approach of cheapest-flexible-duct-wins is fading at the top end of the market and being challenged at the volume end by NCC 2022 thermal performance requirements.

NCC 2022 — 7-star NatHERS and Section J

The 2022 edition of the National Construction Code took effect for residential from 1 May 2023 (with state transition arrangements extending to 1 October 2023 in some jurisdictions). Three changes matter for HVAC ductwork:

• NatHERS minimum 7 stars — up from 6 stars under NCC 2019 for new Class 1 dwellings. Higher star rating means tighter envelope, higher insulation values, lower air leakage, lower heating and cooling loads. HVAC equipment sizes drop by 20–30 percent on the same floor plan, and duct sizing should drop with them — reusing 6-star duct sizing on a 7-star envelope produces over-cooling, short-cycling and uncomfortable mean radiant asymmetry.
• Whole-of-home energy use cap — separate to the NatHERS thermal model, NCC 2022 caps total household energy use including HVAC, hot water and lighting. HVAC efficiency (system COP, fan power, duct leakage) directly impacts the whole-of-home compliance margin.
• Section J updates (Volume 1 commercial, applicable to apartment common areas) — duct insulation R-values, equipment efficiency minimums, plant room ventilation requirements all tightened.

The combined effect is that duct leakage, duct insulation and HVAC system efficiency all matter for compliance — not just for utility bills. Mechanical specifications that previously allowed Class A duct leakage (3.0 L/s/m² at 400 Pa, achievable with average flexible duct installation) are increasingly tightening to Class B (1.0 L/s/m²) or Class C (0.34 L/s/m²) for projects targeting 7.5+ stars or premium NABERS ratings.

The electrification mandate

Victoria's gas connection ban — announced 28 July 2023, effective 1 January 2024 — prohibits new residential gas connections for all new homes and residential subdivisions requiring a planning permit. The ACT enacted similar legislation. New South Wales is staging a slower phase-out via the Net Zero Plan. Queensland and Western Australia have not yet announced equivalent measures.

For HVAC ductwork in VIC and ACT new residential, the consequence is an immediate pivot away from ducted gas heating (historically dominant in Melbourne and Canberra detached housing) to ducted reverse-cycle heat pump. Ducted gas systems typically delivered 14–22 kW heating capacity through large supply trunks at high air volume and high supply temperature (60–70 °C). Heat pumps deliver a typical 8–14 kW heating capacity at lower supply temperature (35–50 °C), which means longer run times and higher airflow per kW of room load. The duct system must be sized accordingly — direct substitution of a gas furnace with a heat pump in an existing duct system typically results in inadequate room comfort and noisy operation.

The new-build implications are cleaner: every VIC and ACT residential project from 2024 onwards is designed around heat pump heating from day one, with the duct system sized appropriately. The NSW transition will be more gradual and is creating an interesting mid-term market for retrofitting existing ducted gas systems to heat pump.

NCC 2022 standards reference — what binds residential ductwork

The Australian residential HVAC duct specification stack is layered. NCC sits on top, referenced AS/NZS standards underneath, with state-specific overlays in some jurisdictions. The key references are:

NCC 2022 Volume 2 — Class 1 and 10 buildings

Volume 2 (the Housing Provisions) governs detached houses, townhouses, duplexes and non-habitable structures. The HVAC-relevant parts:

• Part 13.7 Heating and cooling — minimum efficiency and capacity requirements for HVAC equipment.
• Part 13.6 Sealing of the building envelope — air-tightness requirements that interact with duct system pressure-stabilisation.
• Part 10.6 Sound insulation — Rw + Ctr requirements for inter-tenancy walls in attached dwellings.
• Part 10.8 Ventilation — natural and mechanical ventilation requirements for habitable rooms, kitchens, bathrooms and laundries.
• NatHERS pathway — 7-star minimum thermal performance (1 May 2023 onwards).

NCC 2022 Volume 1 — Class 2 and 3 buildings

Volume 1 governs apartments (Class 2), serviced apartments and student accommodation (typically Class 3), retirement villages (mixed) and aged care (Class 9c). The HVAC-relevant sections:

• Section E2 Smoke hazard management — fire-isolated stair pressurisation, smoke control, smoke exhaust. Drives stair pressurisation duct specification.
• Section F Health and amenity — Section F2 sound insulation (Rw + Ctr ≥ 50 dB inter-tenancy), Section F4 light and ventilation, Section F6 condensation management.
• Section J Energy efficiency — Section J3 building envelope, J5 services, J6 lighting. J5 governs HVAC duct insulation, plant room ventilation and equipment efficiency.
• Section C Fire resistance — fire-rated construction, including duct penetrations through fire-rated walls and floors.

AS/NZS reference standards

• AS 1668.1:2015 — The use of ventilation and air-conditioning in buildings — Fire and smoke control. Stair pressurisation, smoke spill, smoke exhaust.
• AS 1668.2:2024 — The use of ventilation and air-conditioning in buildings — Mechanical ventilation. Outdoor air rates, exhaust rates for sanitary spaces and kitchens, contaminant control.
• AS 4254.1:2012 — Ductwork for air-handling systems — Flexible duct.
• AS 4254.2:2012 — Ductwork for air-handling systems — Rigid duct (replaces and incorporates the older AS/NZS 4254 single-document edition).
• AS 1530.4:2014 — Methods for fire tests on building materials, components and structures — Fire-resistance tests for elements of construction. Reference standard for fire damper and smoke damper testing.
• AS/NZS 2107:2016 — Acoustics — Recommended design sound levels and reverberation times for building interiors. Bedroom NC-25 to NC-30, living room NC-30 to NC-35, kitchen NC-35 to NC-40.
• AS/NZS 4859.1:2018 — Thermal insulation materials for buildings — General criteria and technical provisions. Reference for duct insulation R-value calculation.
• AS/NZS 3666.1:2011 — Air-handling and water systems of buildings — Microbial control. Reference for duct cleanability and access.
• ASHRAE 62.2 — Ventilation and Acceptable Indoor Air Quality in Residential Buildings. Often referenced in international developer specifications and increasingly cross-referenced in Australian premium specifications.

Single-family ducted reverse-cycle — the volume play

The classic Australian detached house ducted reverse-cycle system is the highest-volume residential HVAC application by far. Understanding its anatomy is the foundation for everything else in residential.

System sizing

For a 200 m² single-storey detached house at NCC 2022 7-star NatHERS in Melbourne (climate zone 6) the typical load is 8–12 kW total cooling and 7–11 kW total heating. Size the system to the higher of the two — in southern Australia generally heating, in tropical Brisbane and Darwin generally cooling. Two-storey homes of equivalent floor area typically need 10–14 kW cooling and 9–13 kW heating because of higher upper-floor solar gain and roof exposure.

Indoor unit location and ceiling void

The indoor unit (ducted fan-coil with reverse-cycle direct-expansion coil) is located in the ceiling void above a service area — typically a hallway or laundry. Required ceiling void clearance is 350–450 mm above the false ceiling for the unit, drain pan and supply trunk takeoff. Coordinate with the architect during preliminary design — late-stage discovery of inadequate ceiling void clearance is the single most common cause of mechanical re-design on residential projects.

Supply duct distribution

Supply ducts run from the indoor unit through the ceiling void to ceiling diffusers in each conditioned room. Sizing rules of thumb:

• Trunk friction rate 0.8–1.0 Pa/m for rigid duct, 1.0–1.5 Pa/m for flexible duct.
• Trunk velocity 4–6 m/s, branch velocity 2–4 m/s, diffuser face velocity 1.5–2.5 m/s in bedrooms (acoustic-driven), 2.5–3.5 m/s in living areas.
• Branch length under 6 m for flexible insulated duct (longer runs accumulate excessive pressure drop). Use rigid trunk with short flexible drops at diffusers for runs over 6 m.

Return duct architecture

Most Australian residential ducted reverse-cycle uses a single central return grille — typically located in a hallway ceiling, sized at 60–80 percent of the supply free area to minimise pressure drop and acoustic regeneration. The return path relies on undercut doors or transfer grilles to allow air to migrate from each conditioned room back to the central return. The single-return approach is cheap and works adequately on small homes but on larger floor plans (over 250 m²) the lack of room-by-room return drives temperature stratification — multiple return grilles are recommended on premium specifications.

Zoning

Single-thermostat ducted reverse-cycle is functionally adequate but compromises occupant comfort because every room conditions to the temperature the thermostat sees in the hallway. Zoning — motorised dampers in branch ducts driven from individual room thermostats — is now standard on premium specifications and increasingly common at the volume end. Zoning hardware adds 800–1,500 AUD per zone in equipment cost and requires:

• Variable-speed (ECM) indoor fan motor to track partial-zone load without over-pressurising the system.
• Branch ducts sized for the open-zone airflow plus a margin for damper closure differential.
• Bypass arrangement (typically a barometric bypass damper from supply trunk to return) to relieve fan overpressure when zones close.
• Tight-closing dampers (Class 2 leakage minimum) so that closed zones actually shut off — leaky dampers waste energy and undermine zone setpoints.

Material specification

The default volume-builder specification is flexible insulated ducting throughout — fast to install, cheap, fits in tight ceiling voids — at the cost of a 10–15 year service life and higher pressure drop. Premium custom homes increasingly specify rigid galvanised G90 trunks with TDF flange joints and sealed Pittsburgh seams, with flexible drops only at the final 1–2 m to the diffuser. The premium specification adds 30–60 percent to the duct package cost but lasts 30+ years and is cleanable to AS/NZS 3666.1.

Apartment HVAC architecture — four common patterns

Apartments diverge from detached housing because of inter-tenancy fire and acoustic requirements, common-area ventilation and the architectural challenge of getting fresh air, exhaust and refrigerant pipes in and out of every unit through restricted facade and shaft space.

Pattern A — Individual split system per apartment (most common)

The dominant low-cost solution. Each apartment has its own outdoor unit on a balcony, rooftop plinth or facade-mounted condenser frame, and an indoor unit in a ceiling cavity (ducted) or wall-mounted (split). No HVAC duct is shared between apartments — the only inter-tenancy mechanical services are bathroom and kitchen exhaust risers and corridor ventilation. Refrigerant pipework is short, no chilled water distribution, no central plant. Tenant comfort is fully under occupant control.

The trade-off is facade aesthetics (visible condenser units), maintenance access (individual unit failures) and limited ventilation (most splits do not provide outdoor air, requiring separate ventilation strategy). For volume apartment projects the cost saving is decisive — most Meriton, low-rise developer and apartment delivery uses this pattern.

Pattern B — Ducted reverse-cycle per apartment (premium)

Each apartment has its own ducted reverse-cycle system with indoor unit in ceiling void and supply distribution to all rooms. Trunks galvanised, branches flexible or rigid depending on specification. The result mirrors single-family ducted reverse-cycle inside each apartment, with the additional inter-tenancy and shaft requirements of Class 2 construction. Common in Mirvac, Frasers, Crown Group and high-end Lendlease apartment specifications.

Pattern C — Central plant with FCUs (high-end and Build-to-Rent)

Central chiller and boiler plant (or central air-source/water-source heat pump) on rooftop or in basement plant room, two-pipe or four-pipe water distribution risers, fan coil unit (FCU) in each apartment ceiling cavity. The FCU has chilled water and/or heating water supply, blower fan, condensate drain, and supply and return duct distribution to room diffusers.

Advantages — single maintenance point for plant, lower per-apartment electrical capacity, higher overall system efficiency, single commissioning point. Disadvantages — central plant operating regime determines tenant comfort, plant downtime affects every unit, capital cost is higher per apartment.

Common in premium Lendlease, Frasers, Mirvac high-rise apartments and most Build-to-Rent schemes (Greystar, Mirvac BtR, Frasers BtR).

Pattern D — Dedicated outdoor air system (DOAS) plus FCU or split

The DOAS approach decouples ventilation from cooling. A central DOAS plant on the rooftop conditions outdoor air to neutral or slightly cool/dry, distributes via vertical risers and corridor branches to a tempered fresh-air supply diffuser in each apartment. Sensible cooling and heating is provided locally — by FCU (if a central water plant exists) or by individual splits. The split-DOAS hybrid is increasingly popular because it achieves engineered ventilation rates without the capital cost of full central plant.

The DOAS pattern is consistent with ASHRAE 62.2 ventilation rates and is becoming more common as NCC tightens ventilation requirements in Class 2 buildings. Build-to-Rent schemes increasingly specify DOAS-plus-split as the default architecture.

Bathroom and kitchen exhaust — AS 1668.2 minimum rates

Residential exhaust ventilation is governed by AS 1668.2:2024 with NCC 2022 Section F (Volume 1) or Part 10.8 (Volume 2) requiring mechanical ventilation in spaces without natural ventilation. The minimum exhaust rates are:

• Sanitary spaces (toilets, bathrooms, ensuites) — 25 L/s continuous or 40 L/s intermittent on occupancy.
• Domestic kitchens — 40 L/s continuous or 50 L/s intermittent over the cooking appliance.
• Laundries — 25 L/s continuous or 40 L/s intermittent on occupancy.

Apartment bathroom exhaust ductwork

The standard apartment bathroom exhaust uses a vertical galvanised riser shared between stacked apartments, with individual fan units in each apartment discharging to the common riser. Each apartment has a bathroom or ensuite ceiling exhaust grille, ductwork to a wall-mounted or in-line fan, then a connection to the riser through a fire damper at the apartment boundary. The riser is typically 200–300 mm diameter rigid galvanised, sized for the cumulative flow with diversity factor (typically 0.5–0.7) on the basis that not every apartment exhausts simultaneously.

The fire damper at the apartment boundary is mandatory per AS 1530.4 — typically 60/60/60 minutes FRL matching the inter-tenancy floor or shaft wall. The shaft itself is fire-rated construction with FRL matching the building. Top-of-shaft termination has a rooftop relief or powered roof fan with weather hood and bird mesh.

Kitchen exhaust ductwork

Domestic range hood discharge generally goes direct to outside through a wall, soffit or roof cap with a backdraft damper to prevent reverse airflow. In apartment buildings where direct external discharge is not architecturally feasible (interior kitchens, deep floor plates), a shared kitchen exhaust riser may be required. Smooth-bore galvanised duct is essential — flexible duct is unsuitable for kitchen exhaust because the convolutions accumulate grease deposits that become a fire hazard. Riser cleaning access points must be provided per AS/NZS 3666.

For premium apartments and serviced apartments with full residential kitchens, consider over-spec sizing — the AS 1668.2 minimum is a baseline, not an optimum. Air-tight kitchens over a high-output induction or gas cooktop generate significant moisture, particulate and odour that 40 L/s does not always clear adequately.

Stairwell pressurisation — Class 2 high-rise requirement

NCC 2022 Volume 1 Section E2 requires fire-isolated stairs in Class 2 buildings above defined storey thresholds to be mechanically pressurised to maintain a smoke-free egress path during a fire. AS 1668.1 provides the design methodology. Key requirements:

• Pressurisation level — 50 Pa nominal positive pressure relative to the fire compartment (the floor on fire). This pressure is what prevents smoke ingress when stair doors are closed.
• Door-opening transient — when occupants open a stair door to egress, pressure drops momentarily. Design must accommodate door-opening velocity and provide enough fan capacity to recover pressure quickly.
• Relief at top of shaft — pressure relief damper or open vent to prevent over-pressurisation that prevents door operation. Typical relief setpoint is 60–80 Pa.
• Supply fan — typically located on the roof or dedicated plant deck, sized for the design air change rate plus door-opening transient. Variable-speed fans with pressure-controlled output are increasingly standard.
• Riser ductwork — galvanised rectangular or round duct, sized for 5–8 m/s velocity, AS 4254 Class C duct leakage minimum because leakage directly degrades shaft pressure. Hot-rolled steel sheet 1.0–1.6 mm thick is typical for stair pressurisation risers in tall buildings.

Lift-shaft venting and corridor pressurisation in some designs require additional dedicated risers. In a high-rise apartment tower the smoke-control system can include three or four parallel vertical riser systems (stair pressurisation, lift shaft venting, corridor pressurisation, smoke exhaust). Coordination with the fire engineer at preliminary design is essential — late-stage smoke-control duct design adds significant cost and architectural impact.

See our fire and smoke damper integration guide for detailed coordination of smoke-control duct components.

High-rise apartment HVAC — the integrated picture

A 30-storey apartment tower in Sydney or Melbourne is the most complex residential HVAC project in Australia. The duct system typically includes:

• Per-apartment air-conditioning — individual splits, ducted reverse-cycle or FCUs depending on architecture pattern.
• Per-apartment kitchen exhaust — direct or shared riser.
• Per-apartment bathroom exhaust — shared riser with fire damper at apartment boundary.
• Corridor ventilation — supply or extract via ceiling void, typical galvanised duct ring main per floor.
• Stair pressurisation — supply riser with rooftop fan, AS 4254 Class C duct leakage.
• Lift shaft venting — dedicated smoke spill riser if required by the fire engineering report.
• Smoke exhaust — basement carpark exhaust, lobby smoke exhaust, depending on smoke control strategy.
• Plant room HVAC — dedicated ventilation for chiller, boiler or heat pump plant rooms; lift motor rooms; switchboard rooms.
• Carpark ventilation — basement parking requires CO-controlled supply and exhaust per AS 1668.2.
• Amenity space HVAC — building common amenities (pool, gym, lounge, function room) each require their own ventilation per AS 1668.2 with appropriate exhaust for swimming pool dehumidification.

The total duct package on a 200-apartment tower runs 25,000–40,000 m of rigid galvanised duct plus another 8,000–15,000 m of flexible duct in apartment branches. Fabrication time on a high-throughput auto duct line such as the SBAL-V is 12–18 weeks of single-shift production, with parallel spiral round duct fabrication for risers via a tubeformer. Sequencing delivery to match site progress is essential — duct stored in damp conditions on a construction site loses its CR coating and becomes a corrosion problem.

Acoustic considerations — NC-25 to NC-30 in apartment bedrooms

AS/NZS 2107:2016 design sound levels are the binding criterion for residential HVAC noise. The design point in an apartment bedroom is NC-25 to NC-30, equivalent to LAeq 30–35 dB(A). Achieving this requires careful attention across the entire HVAC chain:

Equipment noise

Indoor unit and outdoor unit selection must align with the bedroom NC criterion. A typical 4–6 kW domestic ducted reverse-cycle indoor unit operates at 35–45 dB(A) at the unit casing. With the unit in the ceiling void above a hallway and ducted distribution to bedrooms, achieving NC-25 to NC-30 at the bedroom diffuser requires duct attenuation through length, fittings and lining.

Diffuser face velocity

Diffuser face velocity must be 1.5–2.5 m/s in bedrooms — exceeding this generates regenerated noise above the bedroom NC criterion. In living rooms, where the design point is NC-30 to NC-35, face velocity can climb to 2.5–3.5 m/s. Diffuser selection (linear, square, round, swirl) affects pressure drop and noise generation — manufacturer's data sheets provide NC ratings at design face velocity.

Duct fittings

Sharp transitions, abrupt elbows and undersized fittings generate regenerated noise. Long-radius elbows, gradual transitions and properly sized fittings keep regenerated noise below the NC criterion. Flexible-to-rigid duct transitions require taped, banded or proprietary fittings to prevent rattle and air leakage that become acoustic and energy paths.

Acoustic lining and attenuators

Where duct passes through or above a critical acoustic space, internal acoustic lining (typically 25–50 mm fibre with perforated steel inner liner) provides broadband attenuation. For lower-frequency requirements or higher attenuation, packaged acoustic attenuators are inserted into the duct run. Lined duct adds 30–50 percent to the duct cross-section to maintain the same internal free area, so coordinate sizing during preliminary design.

Inter-tenancy duct seal

NCC 2022 Volume 1 Section F2 requires Rw + Ctr ≥ 50 dB between sole-occupancy units. Where a duct or service penetrates an inter-tenancy wall or floor, the penetration must achieve both the fire-resistance level and the acoustic insulation rating. Use proprietary fire-rated acoustic seals with mineral wool packing and intumescent collars. This is the single most common acoustic non-compliance found at handover — a fire collar that is acoustically transparent.

See our acoustic HVAC duct lining and attenuator guide for detailed specifications.

Flexible ducting versus rigid metal — the lifecycle case

The single most-debated specification choice in residential HVAC ductwork is flexible insulated duct versus rigid galvanised duct. The honest answer is they serve different markets and a project should pick the right tool:

Flexible insulated duct

• Construction — polyester core (typically 25 micron polyester film), helical wire reinforcement, fibreglass or polyester insulation jacket, aluminium foil outer skin.
• Standard — AS 4254.1:2012.
• Advantages — fast installation in restricted ceiling voids, low capital cost (typically 30–50 percent of rigid duct on equivalent project), conforms to irregular routes without custom fittings.
• Disadvantages — high pressure drop (typically 3–5 times rigid duct equivalent length), higher noise generation in the convolutions, 10–15 year service life (UV embrittlement of outer foil, mechanical damage from trades, internal collapse over time), not cleanable to AS/NZS 3666 standards, leakage class generally below Class A unless installation is exceptional.
• Best applications — final 1–2 m drop from rigid trunk to ceiling diffuser, branch runs under 6 m, volume builder housing where 10–15 year replacement cycle is acceptable, retrofit applications in difficult ceiling voids.

Rigid galvanised duct

• Construction — galvanised G90 (Z275) zinc-coated steel to AS 1397, 0.55–0.8 mm gauge for residential applications, joined by Pittsburgh seam (longitudinal) and TDF flange or slip-on joints (transverse).
• Standard — AS 4254.2:2012.
• Advantages — 30+ year service life, cleanable per AS/NZS 3666.1, achievable Class B or Class C duct leakage when fabricated and installed correctly, low pressure drop, low regenerated noise, full compatibility with NatHERS air-tightness modelling.
• Disadvantages — higher capital cost, requires fabrication off-site or on a fabrication shop floor, requires factory fabrication equipment (auto duct line, plasma table, beading rolls, TDF flange former), longer installation time on site for rectangular sections, larger ceiling void requirement than the equivalent flexible duct because rigid duct does not accommodate tight bends.
• Best applications — supply trunks and risers on any project where the long-term operating cost matters, all Build-to-Rent and premium apartments, all stair pressurisation and smoke-control ductwork (rigid is mandatory), all kitchen exhaust ductwork (grease deposition makes flexible unsuitable), retirement village and aged care HVAC, anywhere AS/NZS 3666 cleanability is required.

The hybrid specification

The pragmatic best-practice specification on Australian residential projects is hybrid — rigid galvanised trunks and risers with flexible drops to diffusers. This delivers most of the durability and leakage benefit of rigid duct at most of the installation speed of flexible. The extra cost over a fully-flexible installation is typically 20–40 percent on the duct package, with an offsetting saving on lifetime maintenance, energy and replacement.

Materials specification — galvanised, flexible, fibreglass duct board

Australian residential HVAC ductwork uses three primary material families:

Galvanised steel sheet

The dominant rigid duct material. Specifications referenced:

• AS 1397 — Continuous hot-dip metallic coated steel sheet and strip — Coatings of zinc and zinc alloyed with aluminium and magnesium.
• Coating mass — Z275 (G90 in imperial, 275 g/m² total both sides) is standard for HVAC duct. Heavier coatings (Z350) for marine or aggressive environments.
• Sheet thickness — 0.55 mm (24 ga) for branch ducts, 0.6–0.7 mm (22–24 ga) for trunks, 0.8–1.0 mm (20–22 ga) for risers and large rectangular trunks, up to 1.6 mm (16 ga) for stair pressurisation risers in tall buildings.

Galvanised sheet is roll-formed, sheared to length, notched and folded into duct sections on an auto duct line such as the SBAL-V. Round duct sections are spiral-wound on a tubeformer for sizes from 80 mm to 1,500 mm diameter.

Flexible insulated duct

The dominant residential mass-market duct. Specifications:

• AS 4254.1:2012 — Ductwork for air-handling systems — Flexible duct.
• Inner core — 25 micron polyester film with helical galvanised wire reinforcement, sized 100–500 mm internal diameter typical.
• Insulation — fibreglass (R0.6, R1.0, R1.5) or polyester-fibre (R0.6, R1.0). Polyester is increasingly preferred for low-VOC and dermal-comfort reasons during installation.
• Outer jacket — aluminium foil with polyester reinforcement scrim, sealed at joints with foil tape or proprietary mastic.

Fibreglass duct board

Less common in Australian residential than in North America but used in some applications — pre-insulated rigid panel duct fabricated from fibreglass core with fire-retardant facing on both sides. Provides combined duct + insulation in a single product. Cleaning and durability concerns have limited adoption in cleaner-air-conscious markets, but some volume builder and retrofit applications still use it.

Townhouse and duplex HVAC — same as detached, plus party wall

Townhouse and duplex HVAC mirrors detached single-family in nearly every respect — Class 1a NCC Volume 2 governance, 7-star NatHERS, ducted reverse-cycle dominant, individual ducted system per dwelling. The added requirement is the party wall.

Any duct that crosses the party wall — typically only bathroom or kitchen exhaust if architectural constraints force it — must have a fire damper to AS 1530.4 with FRL matching the wall (typically 60/60/60 minutes for Class 1 attached construction). Acoustic separation per NCC Volume 2 part 10.6 (formerly H1.7) requires Rw + Ctr ≥ 50 dB across the party wall, which means the fire damper assembly must achieve both fire and acoustic ratings — proprietary fire-rated acoustic dampers are available from major suppliers.

Indoor unit ceiling cavities must not span the party wall. Best practice locates each dwelling's indoor unit fully within its own roof-space envelope, with no service access from the neighbour. Outdoor units on shared boundaries require careful acoustic siting — one party's outdoor unit can become the neighbour's nuisance noise source under EPA Victoria, EPA NSW or equivalent state regulations.

Retirement village HVAC — independent living plus high-care wing

Retirement villages combine multiple NCC classifications. Independent living units (ILUs) are typically Class 1a (detached), Class 1b (small attached) or Class 2 (apartments above each other), depending on architectural form. The high-care wing — assisted living and aged care — is Class 9c residential care with healthcare-grade ventilation requirements.

Independent living units

HVAC mirrors apartment or detached residential — individual ducted reverse-cycle, AS 1668.2 ventilation, AS/NZS 2107 acoustics. Specific considerations for retirement living:

• Lower bedroom NC criterion — older residents sleep more lightly and noise tolerance reduces.
• Higher ventilation rates in some designs to manage odour from incontinence aids and medication.
• Easier maintenance access — ceiling-cavity indoor units must be accessible without entering the unit (rooftop, hallway, plant room access where possible).
• Emergency call integration with HVAC (some operators specify HVAC fail-safe to last operational setpoint on emergency).

High-care wing

Closer to a hospital ward than to residential. NCC Class 9c with ventilation requirements approaching ASHRAE 170 lite (the healthcare facilities standard) — typically 6–10 air changes per hour, dedicated dirty-air exhaust from soiled utility and bathing areas, infection control duct surface specification. Rigid galvanised duct mandatory (no flexible duct in healthcare-grade applications) with internal duct surfaces smooth and non-porous to AS/NZS 3666 cleanability.

Student accommodation HVAC — hotel-like with shared facilities

Purpose-built student accommodation is classified Class 3 with HVAC architecture similar to a hotel guest room — individual ducted FCU or split per unit, central DOAS for corridors, central plant for hot water and (in premium schemes) chilled water. Where the design includes shared kitchens and bathrooms (cluster-flat configuration), the ventilation requirements step up to higher rates per AS 1668.2 because of higher occupancy density and shared facility loads.

Major operators include UniLodge, Scape, Iglu, UniGroup, Y Suites and Atira. Mechanical specifications generally follow tier-1 hotel approach — rigid galvanised throughout, FCU per unit with thermostatic control, AS/NZS 2107 acoustic compliance, 24/7 ventilation operation.

SBKJ machinery for residential HVAC duct production

Most Australian residential HVAC duct fabrication runs on a small handful of machine families. SBKJ supplies the high-throughput end of this market:

SBAL-V auto duct line

The SBAL-V is SBKJ's auto duct line for high-volume rigid galvanised rectangular duct fabrication. Single-shift output 200–350 m per shift depending on duct size mix and material thickness. Sheet input 0.5–1.6 mm galvanised G90 from coil. Output is fully formed rectangular duct with TDF flange, beaded longitudinal seam and pre-marked branch takeoff locations. The SBAL-V is the right machine for an Australian fabricator quoting 25,000–40,000 m duct packages on apartment towers, premium custom homes and Build-to-Rent schemes.

See our full auto duct line catalogue for detailed specifications.

SBTF spiral tubeformer

The SBTF spiral tubeformer produces round galvanised duct sized 80–1,500 mm diameter from coil. Single-shift output 800–1,500 m per shift depending on diameter. Round duct is the preferred form for stair pressurisation risers, kitchen exhaust risers, bathroom exhaust risers and any high-velocity supply application — round duct is structurally stiffer per kilogram of steel, lower pressure drop than equivalent rectangular, and easier to clean to AS/NZS 3666.

See our spiral tubeformer catalogue.

TDF flange forming

The TDF (Transverse Duct Flange) joint is the dominant transverse joint method on Australian rigid galvanised duct. Continuous integral flange formed from the duct sheet itself, tightened with cleats and corner bolts. AS 4254 Class B or Class C leakage achievable with sealed TDF — significantly tighter than slip-on flange or angle iron joints. SBKJ TDF forming is integrated into the SBAL-V auto duct line.

What SBKJ does not supply

Flexible insulated ducting is sourced from specialist suppliers (Polyaire, Holyoake, Kingspan, Owens Corning) and is outside SBKJ's scope. Fire and smoke dampers are sourced from specialist damper manufacturers (Trox, Ruskin, Halton, Kingspan and others) and are not SBKJ-fabricated. SBKJ supplies the rigid galvanised duct fabrication equipment that produces the galvanised trunks, risers and rigid branches that interface with these third-party components on a complete residential HVAC project.

Australian housing capex programmes — where the work is

For an HVAC duct fabricator deciding which residential pipeline to chase in 2026, the active capex programmes are:

• Housing Australia Future Fund (HAFF) — federal AUD 10 billion social and affordable housing programme. Delivered through community housing providers and state programmes. NCC minimum specifications, ducted reverse-cycle dominant.
• NSW Homes — state-government social housing programme, multi-billion AUD, working with NSW Building Commissioner reforms to lift HVAC quality.
• Homes Victoria — VIC equivalent, with the additional driver of the gas connection ban requiring all-electric HVAC.
• QLD Department of Housing — Queensland social housing programme, Brisbane and regional centres.
• Build-to-Rent (BtR) — institutional asset class delivered by Greystar, Mirvac, Lendlease, Frasers and several international owners. Specifications tighter than typical owner-occupier because the operator owns the operating cost — increasingly specifying rigid duct, DOAS ventilation, central plant.
• Private apartment delivery — Meriton (largest single apartment developer in Australia), Mirvac, Lendlease, Stockland, Frasers Property, Greenland Group, Crown Group, Aria Property Group, Greaves Group continue to deliver private-sale apartments to investor and owner-occupier markets.
• Detached and townhouse delivery — Stockland, Mirvac, Frasers, Lendlease, plus the major detached builders (Metricon, Henley, Burbank, Simonds, G.J. Gardner, Hotondo, McDonald Jones).
• Retirement living — Stockland (largest), Lendlease, Aveo. Aged care delivery dominated by Bolton Clarke, Bupa, Estia, Regis.

The largest residential HVAC duct opportunities by total fabricated metres are concentrated in Build-to-Rent towers, premium high-rise apartments and the social housing pipeline driven by HAFF and state programmes.

Cross-developer specification snapshot

Each of the major Australian residential developers maintains a project-by-project mechanical specification template, generally adapted by the appointed mechanical consultant on each scheme. The patterns we see most often:

• Mirvac — premium specifications across apartments and Build-to-Rent. Rigid galvanised trunks standard, AS 4254 Class B leakage minimum, AS/NZS 2107 strict compliance, central plant for high-rise with DOAS becoming common.
• Lendlease — apartments and Build-to-Rent broadly aligned with Mirvac specifications. Master-planned communities with detached and townhouse use volume builder specifications adapted to NCC 2022 7-star.
• Stockland — large detached and townhouse delivery, retirement living portfolio (largest in Australia). Volume builder approach for detached and townhouse, premium specifications for retirement living independent living units.
• Frasers Property — apartments primarily, with occasional Build-to-Rent. Premium specifications, often LEED Gold or Platinum certified, rigid duct in trunk and riser.
• Meriton — largest single apartment developer in Australia. Cost-driven private sale market focus. Individual splits per apartment with bathroom and kitchen exhaust risers as the dominant pattern. Meriton Suites serviced apartments operate to a tighter specification with ducted reverse-cycle and 24/7 corridor ventilation.
• Greenland Group, Crown Group, Aria Property Group, Greaves Group — high-rise apartment developers in Sydney and Melbourne. Specifications vary by project but generally premium with rigid galvanised duct, AS/NZS 2107 strict compliance, smoke-control duct package on every high-rise.
• Multiplex, Hutchinson Builders, Lendlease Building, Built, Roberts Co — head contractors. They run mechanical sub-contractor pre-qualification and award duct packages to tier-1 fabricators with proven NCC compliance, project finance, ISO 9001 quality systems and demonstrated capacity to deliver on programme.

How SBKJ supports residential HVAC duct fabricators in Australia

SBKJ's Australian customers fabricating duct for residential projects use a typical equipment stack of:

• SBAL-V auto duct line for high-throughput rigid galvanised rectangular duct.
• SBTF spiral tubeformer for round galvanised duct on risers and exhaust applications.
• SBKJ Pittsburgh seam former and TDF flange former integrated into the auto duct line for transverse joint quality consistent with AS 4254 Class B or Class C leakage.
• Plasma cutting table for branch takeoffs, custom fittings and irregular shapes.
• SBKJ technical support from the Australian office (Box Hill North VIC) — English-speaking engineers covering installation, commissioning, spare parts, operator training and ongoing technical advice.

Commissioning support is delivered by SBKJ engineers on site — typically 5–10 days for an initial machine installation, with operator training, written commissioning report and 12-month warranty from commissioning. Spare parts kits ship with the machine and are stocked at the SBKJ Australia office for under-14-day fulfilment to anywhere in Australia. See our Australia operations page for full details.

Talk to an SBKJ engineer about your residential duct programme →

FAQ

Should residential HVAC use rigid metal duct or flexible insulated duct?

Volume builder housing dominantly uses flexible insulated ducting — fast, cheap, fits restricted ceiling voids, but 10–15 year service life. Premium villas, multi-residential apartments above 5 storeys, Build-to-Rent and aged care should specify rigid galvanised trunks with flexible drops only at diffusers, because rigid lasts 30+ years, is cleanable to AS/NZS 3666 and is consistent with NatHERS air-tightness modelling.

What does NCC 2022 7-star NatHERS mean for HVAC duct sizing?

Higher star rating means tighter envelope, lower heating and cooling loads (typically down 20–30 percent from 6-star) and HVAC equipment sizes drop accordingly. Duct sizing must drop with the load — reusing 6-star duct sizing on a 7-star envelope produces over-cooling, short-cycling and uncomfortable rooms. Duct leakage class also tightens because NatHERS now models air-change rate.

How does the Victorian and ACT gas ban affect residential ductwork?

From 1 January 2024 in VIC and similar dates in ACT, new residential gas connections are prohibited. Ducted gas heating is replaced by ducted reverse-cycle heat pump. Heat pump supply temperatures (35–50 °C) are lower than gas (60–70 °C) and require higher airflow per kW for equivalent room comfort, so duct sizing typically increases. Direct substitution into existing duct systems usually produces inadequate heating and noisy operation.

What are the AS/NZS 2107 noise criteria for apartment bedrooms?

AS/NZS 2107:2016 specifies bedrooms NC-25 to NC-30 (LAeq 30–35 dB(A)), living rooms NC-30 to NC-35, kitchens NC-35 to NC-40. For HVAC duct design this drives diffuser face velocity to 1.5–2.5 m/s in bedrooms, demands acoustic lining or attenuators on supply trunks where they pass critical spaces, and requires careful regenerated noise control at fittings and dampers.

What ductwork is required for high-rise apartment stair pressurisation?

NCC 2022 Volume 1 Section E2 requires fire-isolated stairs in Class 2 buildings above defined storey thresholds to be mechanically pressurised to AS 1668.1. Design 50 Pa nominal positive pressure relative to the fire compartment, supply via galvanised riser at 5–8 m/s, AS 4254 Class C duct leakage minimum because leakage degrades shaft pressure, fan on roof or plant deck, relief at top of shaft, door-opening transient analysis with the fire engineer.

Which Australian developers and builders specify residential HVAC ductwork?

Apartments and Build-to-Rent: Mirvac, Lendlease, Stockland, Frasers Property, Meriton, Greenland Group, Crown Group, Aria Property Group, Greaves Group. Detached and townhouse: Stockland, Mirvac, Frasers, Lendlease plus volume builders (Metricon, Henley, Burbank, Simonds, G.J. Gardner, Hotondo, McDonald Jones). Construction: Multiplex, Hutchinson Builders, Lendlease Building, Built, Roberts Co.

What are the AS 1668.2 minimum exhaust rates for residential bathrooms and kitchens?

Bathrooms and ensuites 25 L/s continuous or 40 L/s intermittent. Kitchens 40 L/s continuous or 50 L/s intermittent over the cooking appliance. Laundries 25 L/s continuous or 40 L/s intermittent. Apartment bathrooms typically use a vertical shared riser with fire damper at apartment boundary per AS 1530.4. Kitchen exhaust must be smooth-bore galvanised duct because flexible duct accumulates grease in convolutions.

What is the typical lead time for residential HVAC ductwork on an Australian apartment project?

For a 200–400 apartment Class 2 high-rise, mechanical sub-contractor procurement starts 9–12 months before practical completion. Rigid galvanised duct fabrication on a high-throughput auto duct line such as SBAL-V produces 200–350 m per shift, so a 30,000 m package fabricates in 12–18 weeks single-shift. Spiral round duct from a tubeformer adds parallel capacity. Critical path items are usually plant-room AHUs, fire and smoke dampers and stair pressurisation fans rather than the duct itself.