Tenant fit-out is not base-building — and that distinction drives every decision
The single most common engineering mistake on Australian office tenant fit-outs is treating the project as if it were a new base-building installation. It is not. The base-building HVAC plant — chilled water, central air-handling units, primary supply risers, outdoor-air make-up, smoke spill and stair pressurisation — was specified and built by the landlord, commissioned years or decades earlier, and is fixed in scope. Everything from the in-ceiling tap-off downwards is the tenant's responsibility, and everything above it is somebody else's problem.
This boundary line drives the entire engineering envelope. The tenant fit-out HVAC scope starts at the base-building primary duct tap-off on each floor, the chilled water flow-and-return valves and the condenser water connection points if supplementary cooling is required. It ends at the diffuser face, the return-air grille and the BACnet point list handed over to the building management system. Everything in between — VAV boxes, flexible runouts, acoustic attenuators, fire dampers, smoke dampers, grilles, registers, diffusers, supplementary split systems, in-row coolers, condenser pipework, controls cabling, BMS interface, commissioning and NABERS Tenancy rating — sits within the tenant fit-out package.
For the fit-out builder, this means the HVAC subcontract is bounded by a small number of physical interfaces — usually a single primary supply duct connection per floor zone, plus chilled water and condenser water valves — and a much larger interface set with the tenant's other trades: ceiling, partitioning, joinery, lighting, fire detection, data cabling, security, audio-visual and increasingly distributed antenna systems for in-building 5G coverage. The most expensive mistakes on tenant fit-outs are not the ductwork itself; they are clash-detection failures in the ceiling void and BMS integration scope gaps that surface during commissioning.
The lease structure reinforces this distinction. A base-building lease typically delivers Cat A condition: the floor has primary HVAC supply ductwork, perimeter heating or cooling, a basic ceiling grid, raised access flooring if specified and a finished concrete or carpeted floor. Cat B is the tenant fit-out: partitioning, joinery, branded fit-out elements, IT cabling, supplementary services and the HVAC distribution from VAV boxes down to diffusers. Make-good provisions at lease end usually require the tenant to remove all Cat B work and reinstate Cat A condition — which means the HVAC contractor on the original fit-out is often the same contractor on the make-good five or ten years later.
The Australian regulatory envelope: AS 1668.2, AS 4254.1 and NCC Section J
Three documents define the tenant fit-out HVAC envelope in Australia: AS 1668.2 (mechanical ventilation in buildings), AS 4254.1 (ductwork for air handling systems in buildings, flexible ductwork covered in AS 4254.2) and Section J of the National Construction Code (energy efficiency). Every tenant fit-out drawing set is implicitly underwritten by these three.
AS 1668.2 establishes the minimum outdoor air rate for each space type. For office workspaces, the calculation is V_p × N + V_a × A, where V_p is the per-person outdoor air rate (7.5 L/s per person for office workspace), N is the design occupancy, V_a is the per-area outdoor air rate (0.5 L/s per square metre) and A is the floor area. For a 200 m² open-plan zone at one person per 10 m² (20 people), the AS 1668.2 minimum outdoor air rate is 20 × 7.5 + 200 × 0.5 = 150 + 100 = 250 L/s. Post-COVID hot-desking densities of 8-12 m² per person materially increase the people-based portion of this calculation compared to traditional 12-15 m² densities, which is why so many B-grade towers built in the early 2000s now struggle to deliver enough fresh air at full tenant occupancy.
AS 4254.1 governs the ductwork itself. For commercial office fit-outs the standard reference is Class 2 ductwork — galvanised steel sheet, G300 substrate as a minimum, TDF (transverse duct flange) connections or Pittsburgh seam construction, hanger spacing per the published schedule based on duct cross-section, and a leakage class suitable for low and medium pressure systems. Class 3 ductwork is used for higher static pressure systems such as variable refrigerant flow runouts and chilled beam supply, where leakage tolerance must be tighter. Flexible ductwork between the VAV box outlet and the diffuser must comply with AS 4254.2 and is subject to maximum run-length limits to control pressure loss.
NCC Section J brings energy efficiency requirements to the fit-out, although tenant fit-outs sit in an awkward overlap zone where Section J primarily applies to new building work. The dominant compliance mechanism for office fit-outs is NABERS Tenancy energy ratings combined with Green Star Interiors certification, both of which are voluntary but increasingly mandated by institutional landlords and large corporate tenants. NABERS Tenancy specifically measures the energy used inside the tenant boundary — lighting, plug loads, supplementary cooling and any tenant-controlled HVAC consumption — over a 12-month rolling period.
Fire and smoke compliance is governed by NCC Volume One for the building itself, with AS 1530.4 fire-resistance testing, AS 1668.1 smoke and fire control through fire-isolated stair pressurisation and smoke spill, and AS 5141 for fire-rated ductwork penetrating fire-rated separations. Tenant fit-out work that punctures fire-rated risers, floor slabs or wall separations must reinstate the fire-resistance level with certified fire dampers, fire-rated duct or penetration sealing.
Post-COVID density: 8-12 m² per person is the new normal
The single largest change in Australian office fit-out engineering over the last six years is the post-COVID workplace density shift. Pre-pandemic, mainstream open-plan office density landed at 12-15 m² per person at peak occupancy. Most Australian B-grade and A-grade towers were sized around this figure, including base-building primary outdoor-air capacity, chilled-water plant capacity and toilet provisioning. Many landlord plant rooms were designed at 12-14 m² per person at full tenant build-out.
The hybrid working transition that came out of 2020-2022 produced an apparently contradictory outcome. Floor plate occupancy rates dropped materially — many tenants now see only 50-65% of their badged staff in the office on any given day — but the strategy most large tenants responded with was a smaller leased footprint at higher peak density. Lease consolidation drove headline numbers down. Hot-desking, flexible seating and unassigned workstations drove density up to 8-12 m² per person at peak.
For the HVAC engineer, this is a fundamentally different design problem. Higher peak density at lower average occupancy means the system has to handle a wider operating envelope: high outdoor-air demand on Tuesday-Wednesday-Thursday when occupancy peaks, and very low demand on Monday-Friday and weekends. VAV systems with EC fan boxes and demand-controlled ventilation tied to CO&sub2; sensors are the standard response, and tenants who specified constant-volume systems are now retrofitting to VAV at the next fit-out cycle.
The collaboration and meeting space ratio has shifted in parallel. Pre-pandemic office layouts typically allocated 15-20% of net lettable area to meeting, collaboration and breakout space. Modern tenant fit-outs run 25-35% — sometimes higher in tech and consulting tenants — reflecting the reality that staff come to the office for the things that are hard to do remotely (meetings, mentoring, social bonding, ad-hoc problem solving) and do their focus work from home. The HVAC implication is more cellular and semi-cellular spaces, more variable load profiles, tighter acoustic targets and significantly more VAV boxes per floor than the previous era of open-plan workpoint dominance.
VAV box layout: the heart of the tenant fit-out HVAC scope
Variable air volume boxes are the central component of almost every Australian office tenant fit-out HVAC system. The base-building supplies primary conditioned air at a constant temperature (typically 12-14°C supply, sometimes warmer in chilled-beam-equipped towers) through main supply ducts on each floor. The VAV box throttles the air volume delivered to each zone in response to that zone's thermostat, mixing in reheat coil capacity if winter heating is required. The output of each VAV box feeds four to eight diffusers serving a defined zone of the floor.
The standard zoning rule of thumb for Australian commercial office fit-outs is one VAV box per 50-80 m² of net lettable area. A 1,000 m² floor plate therefore needs 12-20 VAV boxes — more for cellular layouts with executive offices, quiet rooms and small meeting rooms; fewer for an open-plan floor with consistent solar exposure and similar occupancy density across the workpoint area. Premium A-grade fit-outs in legal, financial and professional services tenants run toward the high end, sometimes 25-30 VAV boxes per 1,000 m² floor.
Zone definition is driven by four factors: solar exposure (north, south, east, west and core zones have different cooling load profiles), occupancy pattern (an open-plan workpoint area, a boardroom and a kitchenette each have very different heat loads), acoustic requirement (a quiet room needs its own VAV to allow setback overnight without disturbing the open plan) and architectural cellular separation (any space behind a full-height partition needs its own thermostat).
VAV box sizing depends on zone cooling load. Typical Australian office cooling loads at modern density and lighting levels run 80-110 W/m² including people, lights, equipment and solar gain on perimeter zones. A 60 m² perimeter zone at 100 W/m² carries a 6 kW peak cooling load, which at a 10 K supply-to-zone temperature delta requires roughly 500 L/s of primary air — sized comfortably by a 250 mm diameter primary duct connection to a small VAV box. Interior zones run lighter at 60-80 W/m² and can be larger before requiring a second VAV.
Acoustic attenuation is mandatory upstream of any VAV box serving a meeting room, boardroom, quiet room or any space with an NC-30 or stricter target. Standard practice is a 1.2-1.5 m acoustic attenuator section directly on the primary supply connection, with a second attenuator on the flexible runout to the diffuser if the box is short-coupled. EC fan VAV boxes have lower noise generation than older AC fan boxes and have become standard on premium fit-outs targeting 5-Star or 6-Star NABERS Tenancy.
Ceiling void integration: the most underrated coordination task
Australian commercial office floors typically have 2.7-3.0 m floor-to-floor clear height, of which 2.55-2.7 m is finished ceiling height and the remaining 350-500 mm is the ceiling void. Into that ceiling void must fit primary supply ductwork (often 400-600 mm deep at the riser), VAV boxes (typically 250-350 mm deep), reheat coils, flexible runouts to each diffuser, acoustic attenuators, return air paths back to the floor return air grille, lighting fixtures and their wiring, sprinkler pipework and heads, fire detection cabling and devices, structured data cabling on cable tray, security cabling, audio-visual cabling and increasingly DAS (distributed antenna system) cabling and remote radio units for in-building 5G coverage.
For a 1,000 m² floor the ceiling void typically contains 200-300 metres of primary supply ductwork, 1,500-2,500 metres of flexible runout, 12-20 VAV boxes, 60-120 diffusers and grilles, 80-120 light fittings, 30-60 sprinkler heads, 30-60 smoke detectors, 8-15 DAS antennas, two to four wireless access points per 1,000 m² and 4-8 km of structured data cabling. The clash-detection task during design is non-trivial and is the largest single source of rework on fit-out projects.
Best-practice fit-outs run a clash-detected Revit or Navisworks coordination model with all trades before construction. The HVAC modeller delivers a fully detailed ductwork model including hanger drop-rods, flexible runout routes and clearance zones around access panels. The lighting and ceiling designers deliver their fixture layouts. The fire trades deliver sprinkler and detection device locations. The data cabling and DAS installers deliver their tray routing. The model is reviewed in coordination meetings and clashes resolved before any sheet metal is fabricated.
The HVAC trade typically holds priority for ceiling void real estate because ductwork has the largest cross-section, the longest lead time and the lowest tolerance for re-routing. Lighting and cabling fit around the ductwork. Sprinklers are negotiated with the hydraulic engineer because their head spacing is non-negotiable but their pipework path has more flexibility. DAS and wireless access points need clear coverage lines but the radio units can usually be relocated within a 2-3 m radius without performance impact.
Supplementary cooling: comms rooms, server rooms and high-load spaces
The base-building HVAC system runs during business hours and provides cooling for normal office heat loads — people, lights, computers, perimeter solar gain. It does not run 24/7, and it is not sized to handle continuous high-density IT equipment loads. Every tenant fit-out of any size therefore needs supplementary cooling for the spaces that have heat loads outside the base-building envelope.
The most common supplementary cooling application is the tenant comms room or IT cabinet space. Even a small tenant serving 50-100 staff typically has a comms room hosting two to four 42U racks containing core network switches, distribution patch panels, edge routers, a firewall, a small UPS and possibly a tenant-side telecom demarc. Continuous heat load runs 8-15 kW — sometimes higher if the tenant runs significant on-premises compute. This space must be cooled 24/7 with N+1 redundancy and a temperature alarm tied to the BMS and the tenant facilities manager's after-hours contact.
Standard practice is a dedicated split system, typically a 10-20 kW DX unit with the outdoor condenser mounted on a tenant-allocated condenser deck or on a riser slab. Some fit-outs run two split systems in lead-lag rotation for redundancy. Larger comms rooms with 15-30 kW continuous load may use in-row coolers or small CRAC units mounted directly above the rack line, with chilled water or DX feed from a dedicated tenant chiller skid on the riser.
Larger tenant server rooms supporting more than 20 kW of IT load require a CRAC unit (computer room air conditioner) and dedicated ductwork, with hot-aisle/cold-aisle containment if the rack load justifies it. These rooms also need their own access control, leak detection mat under the raised floor (if applicable), fire suppression by clean agent (FM-200, Novec 1230 or inert gas) and environmental monitoring. The HVAC scope is significantly more involved than a simple split system fit-out and frequently approaches data-centre engineering in microcosm.
Beyond comms and server rooms, other spaces typically requiring supplementary cooling include: large boardrooms with full AV load (50-80 kg of display, audio, video conferencing and lighting equipment generates 3-6 kW continuous), training rooms used outside hours, kitchens with substantial coffee and dishwashing load, executive offices with after-hours work patterns and any tenant amenity space that operates beyond base-building schedule.
Underfloor air distribution (UFAD) retrofit considerations
A small but growing proportion of Australian premium A-grade office fit-outs use underfloor air distribution rather than overhead ductwork. UFAD delivers conditioned air through a pressurised plenum under a raised access floor, with adjustable floor diffusers placed close to occupants. The advantages include better thermal comfort at low supply-air temperatures, more flexibility in workpoint reconfiguration and lower fan energy because air is delivered closer to the breathing zone.
UFAD retrofits in existing buildings are constrained by floor-to-floor height. The raised floor consumes 150-300 mm of vertical space that would otherwise be available as ceiling void or finished ceiling height. Most B-grade Australian towers built before 2000 do not have enough floor-to-floor clearance to retrofit UFAD without sacrificing ceiling height below the comfortable 2.55 m minimum. Newer premium A-grade towers (typically 2010 and later) increasingly specify floor-to-floor heights of 3.6-3.9 m to allow UFAD as a tenant fit-out option.
Where UFAD is feasible, the tenant HVAC ductwork scope changes materially. There is no overhead supply ductwork beyond the base-building primary tap-off into the plenum. The plenum itself becomes the distribution duct. VAV boxes are replaced by underfloor terminal units or local fan-powered terminal units. Floor diffusers replace ceiling diffusers. Return air is taken at high level via the ceiling void back to the riser. The ceiling void is freer for lighting, sprinklers and cabling, but the floor void is congested with structured cabling, power and the air plenum itself.
UFAD acoustic performance is generally better than overhead VAV for open-plan because the primary supply velocity is much lower and the floor diffuser is acoustically benign. But it is less effective in cellular spaces where partitions create dead zones in the plenum, and special partition seals are required to maintain plenum pressure. Most Australian UFAD fit-outs end up with a hybrid system — UFAD for open-plan workpoint areas and conventional VAV overhead for cellular meeting rooms, boardrooms and quiet rooms.
BMS integration and workspace experience platforms
The building management system is the central nervous system of the tenant fit-out HVAC. Every VAV box, every supplementary cooling unit, every zone thermostat, every CO&sub2; sensor, every dampers position and every fan status reports to the BMS. The standard platforms in Australian commercial offices are Tridium Niagara (most common across landlord portfolios), Honeywell Enterprise Buildings Integrator, Schneider Electric EcoStruxure Building and Siemens Desigo CC.
The integration scope for a tenant fit-out is well-defined but contractually sensitive. The tenant fit-out HVAC contractor delivers VAV boxes and supplementary cooling units with BACnet/IP or BACnet MS/TP integration, exposes a defined point list to the BMS network, hands over commissioning documentation and a head-end graphics package that allows the building operator to monitor and override the tenant zones. The boundary is usually a network switch port on the tenant's BMS supervisor controller and a point-list scope matrix agreed at the design stage.
The point list is the contractual battleground. A standard VAV box point list includes: zone temperature setpoint (writable), zone temperature reading, primary airflow setpoint, primary airflow reading, damper position, reheat coil valve position (if hot-water reheat), fan status (if fan-powered), filter alarm and override mode. Premium fit-outs add CO&sub2; reading and setpoint for demand-controlled ventilation, occupancy sensor status and an occupied/unoccupied mode switch. The cost of additional points scales with point count, and a 20-VAV floor with 15 points per box plus 20 supplementary points lands at 320 BMS points — not trivial commissioning effort.
On top of the BMS, premium tenants increasingly deploy a workspace experience platform. Equiem (Australian-headquartered, dominant in premium A-grade Australian landlords) and HqO (US-headquartered, growing presence in Australia via global landlords) provide tenant-facing apps that surface BMS data, allow tenants to book meeting rooms, control room temperature setpoints within bounds, report HVAC complaints and receive proactive notifications about scheduled maintenance. These platforms sit on top of the BMS and require their own data integration scope, usually delivered by a tenant technology integrator separate from the HVAC contractor.
The workspace experience integration adds a tenant-side data feed scope to the HVAC contract. The fit-out HVAC contractor exposes its BMS points; the workspace experience integrator subscribes via API. Typical points consumed are: zone temperature, occupancy status, IAQ readings (CO&sub2;, sometimes VOC and PM2.5), meeting room booking integration with HVAC override and after-hours request workflow. None of this is technically difficult but it requires a clear interface definition at the contract stage.
DAS, 5G and the new co-location challenge
Modern Australian commercial office fit-outs almost universally specify a distributed antenna system to provide in-building cellular coverage. The drivers are simple: external macro-cell coverage does not penetrate modern energy-efficient glazing and concrete cores reliably, especially for 5G mid-band (3.5 GHz n78), and tenants expect their smartphones to work everywhere inside the office.
The DAS scope for a tenant fit-out usually includes 8-15 ceiling-mounted antennas per 1,000 m² floor, plus remote radio units, fibre backhaul to the building's master headend and integration with each carrier's macro network. The antennas are typically 200-300 mm diameter ceiling-mounted units recessed flush with the ceiling tile. They co-locate in the same ceiling void as the HVAC ductwork, lighting, sprinklers and structured cabling.
The HVAC coordination implication is co-location clash management. DAS antennas have coverage line-of-sight requirements that constrain their placement. Ductwork directly below an antenna can cause local signal attenuation and dead zones. Best practice during design coordination is to ensure DAS antennas sit at least 600 mm away from any major ductwork run and at least 300 mm from any fluorescent or LED light fixture (to avoid harmonic interference). The DAS designer typically marks up the reflected ceiling plan with no-go zones and the HVAC designer routes around them.
Power and cabling for DAS remote radio units is another tenant scope, usually delivered by the data cabling subcontractor under a separate trade package. The HVAC contractor coordinates physical clearance but does not deliver the DAS itself. The growing complexity of in-building 5G — with multiple carriers, multiple bands, public safety overlays, and Wi-Fi 6E/Wi-Fi 7 wireless access points sharing the same ceiling void — has made the coordination meeting before sheet metal fabrication a 4-6 week task on premium fit-outs.
Acoustic targets and the meeting-room problem
Acoustic performance is one of the most frequently disputed elements of a tenant fit-out, and HVAC is the dominant noise source in most office workspaces. The Australian commercial benchmark targets are NC-35 for open plan workpoint areas, NC-30 for meeting rooms and training rooms, NC-25 for boardrooms and executive offices and NC-20 to NC-25 for quiet rooms and one-on-one rooms. Specialist spaces such as recording studios or telemedicine consult rooms can require NC-15 or stricter and are typically addressed by dedicated mechanical solutions rather than off-the-shelf VAV.
Meeting the boardroom NC-25 target with a standard VAV system is one of the harder engineering tasks in office fit-out. The dominant noise paths are VAV box fan noise (if fan-powered), reheat coil airflow noise, primary duct breakout, diffuser face noise and cross-talk between rooms via shared ductwork. The standard mitigation is a long acoustic attenuator (1.5-2.0 m of lined ductwork) directly upstream of the VAV box, a second attenuator downstream of the box on each flexible runout to a diffuser, low-noise diffusers selected for NC-20 face noise at design flow, and cross-talk silencers in any duct path that connects to another room.
Acoustic testing at practical completion is increasingly part of the fit-out commissioning scope, particularly on premium A-grade fit-outs and government tenants. The acoustic engineer measures NC levels at typical occupied positions in each space and signs off against the design intent. Failures are expensive to remediate after construction because the ceiling has been finished and reopening it for additional attenuation is a high-disruption rework.
Cross-talk between adjacent meeting rooms via shared ductwork is the single most common acoustic defect on tenant fit-outs. Two boardrooms sharing a primary supply duct can hear each other's confidential conversations through the ductwork unless cross-talk silencers are designed in. The acoustic engineer's mark-up of the ductwork single-line drawing during design coordination is the cheapest way to prevent this; remediation after construction often requires localised acoustic blankets or, in severe cases, reworking the duct routing entirely.
NABERS Tenancy and Green Star Interiors
NABERS Tenancy Energy is the dominant measured-performance rating for Australian office tenant fit-outs. It scores the energy used inside the tenant boundary — lighting, plug loads, supplementary cooling and any tenant-controlled HVAC consumption — over a rolling 12-month period and benchmarks it against the national distribution. The rating is published on a six-star scale, with 6-Star reserved for the top 20% of measured tenancies and 4-Star being mainstream practice.
Most premium A-grade tenant fit-outs target 5-Star NABERS Tenancy as the realistic balance between cost and performance. Achieving 5-Star requires a coordinated set of design choices: LED lighting at sub-7 W/m² lighting power density, efficient task and ambient lighting strategies, BMS-integrated occupancy sensors on all zones, low-leakage AS 4254.1 Class 2 ductwork, EC fans on VAV boxes (not AC fans), demand-controlled ventilation tied to CO&sub2; sensors, efficient supplementary cooling units (typically inverter-driven DX with COP ≥ 4.0) and a tenant metering strategy that separates HVAC, lighting and tenant plug-load consumption so each can be optimised independently.
6-Star NABERS Tenancy is achievable but requires more aggressive design choices: underfloor air distribution or chilled-beam systems to reduce fan energy, motion sensors on every workpoint, plug-load shutdown controls, daylight harvesting on perimeter zones and frequently a tenant-side solar PV contribution if the building allows it. 4.5-Star is the more pragmatic budget target for mid-tier B-grade fit-outs, particularly for tenants who do not have the capital budget for full premium specification.
Green Star Interiors is the Green Building Council of Australia's voluntary rating for office fit-outs. Unlike NABERS, which measures operational performance after the fact, Green Star is a design-and-construction rating that scores the fit-out against criteria including energy, water, indoor environment quality, materials and management. The minimum rating is 4-Star (good practice); 5-Star (Australian excellence) and 6-Star (world leadership) are the targets for premium fit-outs. Major corporate tenants and institutional landlords increasingly require Green Star 5-Star as a minimum specification for new fit-outs.
Materials selection is a growing component of both NABERS and Green Star scoring. Cradle-to-cradle certified ceiling tiles, recycled-content carpet tiles, low-VOC paint, sustainably sourced timber and refurbished or remanufactured task chairs all contribute Green Star points. The HVAC scope contributes through ductwork insulation materials (low-VOC, formaldehyde-free), refrigerant selection (R-32 or R-454B for supplementary cooling rather than the older R-410A) and end-of-lease recyclability provisions.
The Australian tenant fit-out contractor market
The Australian commercial office tenant fit-out contractor market is dominated by a relatively small number of national and regional builders, with significant subcontracted depth in HVAC, electrical, fire and partitioning trades. The mainstream tier-one and tier-two fit-out builders include:
- Schiavello Construction — one of the largest national commercial fit-out builders, particularly strong in Victoria and across institutional tenants. Vertically integrated with Schiavello furniture supply giving them an end-to-end fit-out proposition.
- Saracen Interiors — specialist commercial interiors and fit-out builder with offices in Sydney, Melbourne and Brisbane, focused on premium A-grade tenants and corporate workplace transformation.
- Vivid Group — integrated fit-out plus furniture supplier, strong in NSW and Queensland, increasingly active in premium government and corporate tenants.
- Total Construction — national tier-two builder with significant commercial fit-out portfolio, particularly active in the financial services and professional services tenant base.
- Pegasus Group — specialist commercial fit-out builder with a focus on the corporate workplace sector and a strong presence in Melbourne and Sydney.
- Apex Building Group — Sydney-headquartered commercial fit-out builder with substantial premium A-grade tenant experience.
- Probuild (now part of WBHO Construction after the 2022 restructure) — tier-one national builder with both base-building and large-scale fit-out capability.
- Cor Cordis — commercial interiors and fit-out specialist active across the eastern seaboard.
- Hutchinson Builders — tier-one national builder, particularly strong on large-scale fit-outs combined with base-building refurbishment.
- Built — mid-tier national builder with significant commercial fit-out volume, particularly in the 1,000-5,000 m² range.
The contracting model varies. Most fit-outs run as a head-contract managing-contractor arrangement, with the fit-out builder taking principal responsibility and subcontracting HVAC, electrical, fire and partitioning to specialist trades. Premium fit-outs sometimes use a construction-management arrangement where the trades are directly contracted by the tenant or the project manager. Cost-plus and design-and-construct models are less common but used on time-sensitive lease commitments where speed-to-completion outweighs cost certainty.
Real estate operators and the landlord interface
The Australian commercial office market is dominated by a small number of large institutional landlords and unlisted property trusts. The tenant fit-out HVAC contractor's interface with the landlord is contractual (via the lease and the works approval process) and operational (via the building management team during construction and the BMS interface at handover). The major Australian commercial office landlords include:
- Dexus — one of the largest Australian REITs with a national premium A-grade office portfolio.
- GPT Group — major listed property group with an extensive A-grade office portfolio across Sydney, Melbourne and Brisbane.
- Mirvac — integrated property group with substantial office portfolio across the eastern seaboard.
- Charter Hall — major commercial property fund manager with a deep office portfolio across all states.
- Lendlease — integrated property and infrastructure group with a substantial premium A-grade office portfolio, often newly built and including landmark towers.
- ISPT — industry super fund property trust with a large commercial office portfolio aimed at institutional grade assets.
- Investa — specialist office REIT with a focused premium A-grade portfolio in Sydney and Melbourne CBDs.
- Cromwell Property Group — diversified property fund manager with mid-tier office assets.
- AMP Capital — major property fund manager with substantial office holdings.
- QIC — Queensland Investment Corporation, major institutional property fund manager.
Each landlord runs a Cat A specification that defines the base-building condition delivered to the tenant before fit-out begins. The Cat A spec sets the boundary conditions for the tenant HVAC scope: primary duct tap-off size and location, available chilled water flow and return capacity, condenser water availability for supplementary cooling, BMS integration standard, ceiling grid type if any, raised access flooring if any, perimeter heating or cooling delivery, and outdoor air capacity per square metre. Tenants and their consultants must read the Cat A spec carefully because it defines what the fit-out is starting from and what cannot be assumed.
The works approval process is the formal landlord review of the proposed tenant fit-out. The tenant submits drawings, specifications and a method statement; the landlord's building services team reviews against the Cat A boundary, BMS integration requirements, fire and smoke compliance, structural impact and any tenant-on-tenant impact. Approval typically takes 2-6 weeks and can drive significant design changes if the proposed fit-out exceeds the base-building envelope.
Building services consultants on the design side
Tenant fit-out HVAC design in Australia is delivered by specialist mechanical and building services consultants engaged by the tenant or the tenant's project manager. The major national consultancies active in commercial office fit-out include:
- WSP Australia — global multidisciplinary consultancy with extensive Australian commercial office HVAC experience across both base-building and tenant fit-out.
- Aurecon — major Australian-headquartered engineering consultancy with deep building services capability in Sydney, Melbourne and Brisbane.
- Norman Disney & Young (NDY) — Australian building services consultancy with a strong premium commercial office track record, now part of Tetra Tech.
- Stantec — global consultancy with significant Australian commercial office services capability.
- Beca — New Zealand-headquartered consultancy with substantial Australian commercial office HVAC presence.
- Floth — Australian sustainability and building services consultancy with a strong premium commercial office track record, particularly on Green Star and NABERS-rated fit-outs.
- Cundall — global consultancy with significant Australian commercial office presence, particularly in premium A-grade fit-outs and sustainability consulting.
The consultant's scope on a tenant fit-out typically includes mechanical design, energy modelling for NABERS Tenancy, acoustic design (sometimes a separate acoustic consultant), BMS specification, commissioning specification and tender documentation. On premium fit-outs the consultant remains engaged through construction as the principal's representative for technical compliance and commissioning sign-off.
Lease structures, make-good and the lifecycle decision
Australian commercial office leases are typically 5-10 years for mid-tier tenants and 10-15 years for premium tenants with options to extend. The make-good provision at lease end is one of the most contractually sensitive areas of the lease and has direct implications for the HVAC fit-out specification.
A standard make-good clause requires the tenant to remove all Cat B fit-out work and reinstate the floor to Cat A condition at lease expiry. For HVAC, this means removing VAV boxes, ductwork, supplementary cooling and tenant BMS integration, and restoring the floor to the original primary tap-off points and Cat A diffuser layout. The cost of make-good can run AUD 200-400 per square metre and represents a meaningful end-of-lease liability for the tenant.
Negotiated alternatives include "make-good waived" (the landlord accepts the tenant fit-out as-is at lease end, in exchange for a rent premium or a fit-out contribution reduction), "modified make-good" (the tenant removes only some elements, typically branding and partitioning) or "fit-out incentive amortisation" (the landlord funds part of the fit-out cost in exchange for a longer lease commitment, with the make-good waived). The HVAC scope decisions are influenced by the negotiated make-good provision because the recyclability and reusability of the HVAC equipment affects the end-of-lease cost.
For tenants and consultants, this lifecycle perspective drives equipment selection toward more reusable formats. Modular VAV boxes with standardised connections, premium supplementary cooling units with high resale value, AS 4254.1 Class 2 ductwork with TDF connections that can be re-used on the next fit-out and BMS integration that can be commissioned out cleanly all contribute to lower lifecycle cost. Speciality elements such as custom in-row coolers or bespoke ductwork are higher first-cost and higher make-good cost.
SBKJ machine configuration for tenant fit-out ductwork manufacture
Tenant fit-out ductwork is a fundamentally different production problem to base-building ductwork. The runs are shorter, the duct sizes are smaller, the variety per project is higher and the lead times are tighter. Standard base-building ductwork is manufactured in long, repetitive batches on large auto duct lines. Tenant fit-out ductwork is manufactured in small batches with frequent size changes, typically 200-2,000 m² of duct surface area per fit-out and 6-12 distinct duct sizes per project.
For Australian HVAC ductwork contractors handling tenant fit-out work as a core part of their book, the SBKJ machine recommendation depends on the production mix:
- SBAL-III auto duct production line is the workhorse for small-batch tenant fit-outs. Optimised for fast changeover, accepts coil widths up to 1,250 mm, and outputs full rectangular duct sections with TDF flange in a single pass. For a contractor with 60-80% tenant fit-out workload averaging 500-1,500 m² of duct per project, the SBAL-III delivers the right balance of speed and flexibility. See our SBAL-III vs SBAL-V comparison guide for detailed throughput numbers.
- SBAL-V auto duct production line is the upgrade for contractors handling both tenant fit-outs and large floor refurbishments. The SBAL-V accepts wider coils, higher production speed and supports longer continuous runs without operator intervention. For a contractor with mixed work including full-floor or multi-floor refurbishments at 3,000+ m² of duct per project, the SBAL-V justifies the capital uplift over the SBAL-III through better unit cost on the larger jobs.
- SBTF spiral tubeformer is essential for round duct retrofits. Many older Australian B-grade buildings have round-duct distribution rather than rectangular, particularly on the toilet exhaust, kitchen exhaust and supplementary cooling return-air systems. A tenant fit-out contractor who can fabricate round duct on-demand from coil is materially more competitive than one who has to specify imported pre-fabricated spiral duct. The SBTF runs on the same shop floor as the SBAL line and uses similar coil stock.
The case for in-house ductwork manufacture on tenant fit-out work is strong because of lead time and rework risk. Outsourced ductwork manufacture typically runs 3-5 working days from order to delivery, which is a substantial fraction of the on-site fit-out programme for a fast-track lease commitment. In-house manufacture compresses this to same-day or next-day, allows last-minute design changes to be incorporated without programme impact and eliminates the risk of incorrect duct dimensions arriving on site during the ceiling installation phase.
For a typical mid-tier Australian fit-out contractor handling 15-25 fit-outs per year averaging 1,000 m² each, the SBAL-III generates a payback inside two years on duct cost alone, before considering the programme value of in-house manufacturing. For a larger fit-out specialist handling 30+ fit-outs per year with mixed sizes, the SBAL-V is the better long-run choice.
Programme and procurement: the tenant fit-out timeline
A typical Australian commercial office tenant fit-out runs 12-20 weeks from lease commitment to practical completion, with the HVAC scope occupying weeks 4-16 of that programme. The high-level sequence is: design and approval (weeks 1-4), demolition of Cat A elements requiring removal (week 5), ductwork rough-in and ceiling void services (weeks 6-10), ceiling installation and commissioning (weeks 11-14), finishing trades and FF&E (weeks 13-18) and commissioning and acoustic testing (weeks 17-20).
The HVAC long-lead items that drive programme are: VAV boxes (4-8 weeks from order, longer for premium EC-fan boxes), supplementary cooling units (4-10 weeks for larger CRAC units, 2-4 weeks for standard split systems), acoustic attenuators (3-6 weeks for custom lengths) and any custom ductwork sections not deliverable from stock or in-house manufacture. Lead time risk is the single most common programme failure mode on tenant fit-outs.
For contractors using in-house SBKJ machinery, the ductwork itself becomes a non-critical-path activity — manufactured to site demand within 24-48 hours of cut list confirmation. This shifts the programme risk to the long-lead components and allows tighter overall commitments to tenants. Premium fit-out builders increasingly bid on guaranteed completion dates with liquidated damages exposure, and the contractor who can produce ductwork on demand inside their own shop has a structural programme advantage over a contractor relying on a third-party fabricator with a 5-day queue.
Procurement strategy on premium tenant fit-outs increasingly uses early contractor involvement (ECI) models. Under ECI, the fit-out builder is engaged during the design development phase to provide buildability input, programme advice and trade-pricing benchmarks before the design is locked. This is particularly valuable on HVAC because VAV box quantity, supplementary cooling sizing, BMS scope and acoustic treatment all have material cost implications that are easier to optimise during design than to value-engineer post-tender. ECI also de-risks the long-lead procurement by allowing the contractor to place provisional orders before the lease commitment is fully executed.
Cost benchmarks and budget planning
Indicative all-in HVAC fit-out costs in the Australian market currently run AUD 350-650 per square metre of net lettable area, depending on specification level, supplementary cooling scope, BMS complexity and acoustic targets. The lower end of the range covers a basic refresh of an existing fit-out with reused VAV boxes and minimal supplementary cooling; the upper end covers a premium full-strip fit-out with 5-Star NABERS specification, full BMS integration, multiple supplementary cooling systems and Green Star Interiors 5-Star or 6-Star ambitions.
Component-level benchmarks help with scoping discussions: VAV boxes including primary tap-off and acoustic attenuator run AUD 2,800-4,500 each installed depending on size and EC versus AC fan. Supplementary split systems for comms rooms run AUD 12,000-25,000 installed for a 10-20 kW unit including the outdoor condenser, refrigerant pipework and BMS integration. AS 4254.1 Class 2 ductwork manufactured in-house runs AUD 40-65 per square metre of duct surface area; outsourced manufacture adds 25-40% to this number plus the programme cost. Acoustic attenuators run AUD 600-1,200 per linear metre installed.
The cost split on a typical AUD 500/m² HVAC fit-out is approximately: VAV boxes and primary distribution 35%, supplementary cooling 15-20%, ductwork manufacture 15-20%, controls and BMS integration 10-15%, acoustic treatment 5-8%, commissioning and testing 5-7% and the balance in design fees, services coordination and contingency. For tenants planning capital budgets, the supplementary cooling and BMS scope are the two areas most prone to scope creep and most worth detailed pre-tender definition.
Cross-references and further reading
This guide focuses on tenant fit-out HVAC ductwork. For adjacent project types and deeper reference material, see also:
FAQ
How does office tenant fit-out HVAC differ from base-building HVAC?
Base-building HVAC delivers conditioned air from the central plant to each floor riser and shutoff valve — typically chilled water, primary air handlers and main supply risers. Tenant fit-out HVAC starts from the in-ceiling tap-off point on each floor and distributes air through VAV boxes, flexible ducts and diffusers to the actual workspace. Base-building is the responsibility of the landlord and is usually Cat A. Tenant fit-out is the responsibility of the tenant and is Cat B.
What is the AS 1668.2 fresh-air requirement for a modern Australian office?
AS 1668.2 requires V_p × N + V_a × A, where V_p is 7.5 L/s per person and V_a is 0.5 L/s per square metre for office workspace. For a 200 m² open-plan zone at one person per 10 m² (20 people), the requirement is 20 × 7.5 + 200 × 0.5 = 250 L/s outdoor air. Post-COVID hot-desking at 8-12 m² per person materially increases the people-based portion.
How many VAV boxes does a typical Australian office fit-out need?
One VAV box per 50-80 m² of net lettable area. A 1,000 m² floor plate therefore needs 12-20 VAV boxes — more for cellular layouts with executive offices, fewer for an open-plan floor with consistent solar exposure. Each VAV box typically serves four to eight diffusers.
Do I need supplementary cooling for a comms room?
Almost always yes. Even a small tenant comms room generates 8-15 kW of continuous heat load and base-building cooling shuts down outside business hours. Standard practice is a dedicated split system with N+1 redundancy. Server rooms above 20 kW IT load need CRAC units and dedicated ductwork.
What NABERS Tenancy rating should I target?
5-Star NABERS Tenancy for premium A-grade fit-outs, 4.5-Star for mid-tier B-grade. 5-Star requires LED at sub-7 W/m², BMS occupancy sensors, low-leakage AS 4254.1 Class 2 ductwork, EC-fan VAV boxes and separated metering. 6-Star is achievable with UFAD or chilled beam systems.
What duct standard applies to Australian office fit-outs?
AS 4254.1 Class 2 ductwork is the commercial standard — galvanised sheet metal, G300 substrate, TDF or Pittsburgh seams, hanger spacing per the schedule. Higher static systems may require Class 3. AS 4254.2 covers flexible ductwork. AS 5141 governs fire-rated ductwork through fire-rated separations.
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