Modular & Prefab Construction Factory HVAC Ductwork Guide — DfMA, Volumetric & Panelised

Why modular and prefab factories need a different HVAC playbook

A modular construction factory is not a generic shed. It is a manufacturing plant where the product moving down the line is a complete fragment of a building — a volumetric module, a panelised wall, a bathroom pod, a facade unit — and the contaminants generated along that line are a peculiar superset of every trade that would otherwise have been spread across a site over twelve months. Welding fume from steel framing, MDF dust from joinery, isocyanate vapour from polyurethane adhesives in composite facade lay-down, silica dust from tile cutting in bathroom pods, solvent vapour from spray painting, cementitious dust from on-floor wet trades, and the ordinary thermal load of a 200-person workforce assembling product under a 12 metre clear roof.

The Australian modular construction industry has moved decisively in the last decade from off-the-shelf transportable buildings into a serious manufacturing sector. Hickory Group's Sync platform in Melbourne has shipped tower modules into central business district sites, Modscape has taken premium custom modular into commercial and residential at scale, Strongbuild in Sydney built out the New South Wales Land and Housing Corporation social housing program, Sense of Space in Brisbane delivered 36 Geelong as the tallest modular building in the southern hemisphere at the time of completion, Inhabit Group has industrialised facade prefabrication across the Sydney and Auckland markets, and Fleetwood Building Solutions (previously Searipple) has supplied mining accommodation across Western Australia for BHP, Rio Tinto and Fortescue Metals Group. Nuvolab integrates bathroom pods into Melbourne high-rise residential, Aussie Modular Solutions, Innovative Building & Engineering Solutions (IBES), Loft Constructions modular and GenroSA / Geneva Builders cover the South Australian and Victorian townhouse and dwelling market, and the prefabAUS member factory network now spans every state.

Every one of those factories needs a HVAC ductwork strategy that holds up to NCC compliance, prefabAUS guidance, AS 1668 ventilation, and the day-to-day reality of running a precision manufacturing line that produces a single building module every two to six hours. This guide is the playbook our engineers walk through with the prefab and modular builders we supply duct machinery to. It is opinionated, code-anchored, and written from the perspective of an HVAC duct machinery manufacturer that sits one step upstream of the ductwork contractor — the people who build the SBAL-V and SBTF auto duct lines that the contractor uses to fabricate the duct for the factory in the first place. We are reasonably particular about how the duct gets used.

Regulatory backbone — NCC, prefabAUS and the Australian Standards stack

Every modular and prefab construction factory in Australia inherits the same regulatory backbone whether it builds in Melbourne, Sydney, Brisbane, Perth, Adelaide or regional industrial estates. The Australian Building Codes Board (ABCB) administers the National Construction Code, which in Volume One classifies a modular construction factory as a Class 8 building (a laboratory or factory in which a process or handicraft is carried on for trade, sale or gain) and in Volume Three (the Plumbing Code) governs the wet-services side. The NCC, AS 1668 series and a stack of supporting Australian Standards together form the compliance baseline. prefabAUS and the Master Builders Association Modular Building Council layer industry guidance on top.

The standards that matter for a HVAC ductwork specification in a modular factory:

• NCC Volume One Section F. Mechanical ventilation general requirements, including the cross-reference to AS 1668.2 as the deemed-to-satisfy ventilation rate calculation pathway.
• AS 1668.1. The use of ventilation and air-conditioning in buildings, fire and smoke control. The smoke management baseline for any factory above the size and storey thresholds defined in the NCC.
• AS 1668.2. Mechanical ventilation for acceptable indoor air quality. The day-to-day ventilation rate calculation method used in 90 per cent of Australian factories. See our AS 1668.2 reference for a complete breakdown.
• AS 4254.1 and AS 4254.2. Ductwork specification for sheet metal duct (Part 1 flexible, Part 2 rigid). All factory supply, return and exhaust duct should be manufactured to AS 4254 unless explicitly substituted with stainless or non-ferrous specification.
• AS 4391. Smoke management systems. Required for factories above the NCC area thresholds, particularly volumetric module factories with high-bay configurations and large open work zones.
• AS 3853. Health and safety in welding and allied processes — the regulatory basis for weld fume extraction.
• AS 3600. Concrete structures, governing the slab and any tilt-up or precast elements of the factory shell.
• AS 4100. Steel structures, governing the portal frame and any structural-steel mezzanines or pedestals supporting cranage above the line.
• NFPA 33. Spray application using flammable or combustible materials — adopted in Australia as the de facto standard for spray booth ventilation design in industrial paint zones, supplementing AS 1668 with the booth-specific clauses.

prefabAUS, the peak industry body for the Australian prefab sector, has published a Modular Building Code of Practice that complements the NCC. It is not a regulatory instrument in itself but is widely adopted by certifiers and major modular builders as a quality and process baseline. The MBA Modular Building Council guidance covers similar territory from a contracting-side perspective.

The implication for a HVAC ductwork strategy is straightforward. NCC and AS 1668 set the floor. prefabAUS and MBA guidance set a higher operational baseline. The ductwork system delivered into the factory has to meet both, and the duct itself has to be manufactured to AS 4254. Everything that follows in this guide is anchored to that stack.

Design for Manufacture and Assembly (DfMA) — the change in factory ventilation logic

Design for Manufacture and Assembly is the methodological shift that turned modular construction from a niche transportable-buildings sub-sector into a manufacturing industry. DfMA designs the building to be manufactured — the geometry, the connections, the sequence, the work content — rather than designing the building first and trying to figure out how to manufacture it second. In practice this means a DfMA-aligned modular factory has a predictable, repeated work zoning that does not change between projects in the way a traditional contractor's yard does between jobs.

The ventilation implication is that DfMA factories favour zonal supply and exhaust over diffused whole-building ventilation. The factory floor is divided into stations — coil receiving, steel framing, welding, paint, joinery, MEP rough-in, internal lining, glazing, finish, packaging and module despatch — and each station has its own contaminant profile, its own thermal load, and its own ventilation requirement. This is materially different from the older approach of running a single high air-change-rate make-up air system across the whole hall and treating the contaminants by displacement.

The duct system that supports DfMA-aligned ventilation is therefore a network of trunks and branches with a far higher count of branch take-offs than a comparable single-zone factory. A 6,000 square metre volumetric modular factory might have 14 to 20 ventilation zones, each with its own supply, return and exhaust branches off the main supply trunk and the main return trunk. The HVAC contractor producing that duct in-house on an SBKJ SBAL-V auto duct line will spend more time on branches and transitions than on straight trunk, and the line configuration needs to reflect that — fast change-over between sizes, accurate squareness and length tolerance, and reliable seam quality on the smaller cross-sections.

Volumetric modular factories — the air-change baseline

Volumetric modular is the dominant Australian prefab format for residential and accommodation product. Hickory Sync, Modscape, Strongbuild, Sense of Space, Fleetwood, GenroSA and Aussie Modular Solutions all run volumetric lines in different formats. The product moving down the line is a complete room or apartment, framed, lined, MEP-installed, fitted out and finished, lifted onto a truck at one end of the factory and craned onto a podium at site. The factory air zones reflect that work content.

The standard Australian volumetric modular factory air-change baseline our engineers specify against:

• Coil receiving and steel framing — 4 ACH. Low contaminant generation, large open area. AS 1668.2 dilution rate is sufficient. Galvanised supply and return duct, no special exhaust.
• Welding bays — 4–6 ACH general, plus source extraction. The general ventilation handles thermal and dilution load; weld fume is captured at source by flexible arms or robotic hood extraction ducted to a central cartridge collector. AS 3853 fume class W3 filtration on the collector discharge before re-circulation or atmospheric release.
• Joinery and MDF cutting — 6 ACH, plus LEV at saws and routers. Dust generation is high, particle hazard medium. Local exhaust ventilation at every saw, router, sander and edger ducted to a central baghouse. The general ventilation handles balance.
• Paint and finish — 8–10 ACH with NFPA 33 spray booth. The highest ventilation rate and the strictest separation. See the paint zone section below for the full specification.
• MEP rough-in and internal lining — 4–6 ACH. Moderate dust generation, no chemical hazard. Galvanised duct, balanced supply and return.
• Glazing and facade attach — 4 ACH. Low contaminant generation, large product handling area. Often combined with MEP rough-in zone.
• Finishing and quality inspection — 4 ACH plus tight thermal control. Air quality drives caulking, painting touch-up and finish inspection quality. NC-40 acoustic target.
• Despatch and crane bay — 4 ACH, often natural ventilation supplemented. Large door openings dominate the air-change story. Mechanical ventilation handles the off-cycle hours.

A 6,000 square metre volumetric modular factory at 4–10 ACH across the zones with a 9 metre roof bay translates to between 240,000 m³/h and 540,000 m³/h of total supply and return air. The main supply trunks run at 1,200 to 1,800 mm rectangular for the larger zones and 800 to 1,200 mm for the branches. This is the territory where the SBKJ SBTF-1602 main trunk forming line earns its place in the duct shop — it forms supply trunks up to 1,600 mm wide on a single pass with TDF flange edges integrated.

Panelised systems factories — open frame plus closed panel

Panelised prefab differs from volumetric in that the product is a flat wall, floor or roof panel — open framed, closed and lined, or fully finished — rather than a complete room volume. Inhabit Group, Loft Constructions, and parts of the Hickory and Modscape product mix run panelised lines for specific projects. The factory air zoning is similar in principle but compressed in scale, because a panel is geometrically simpler and the work content per panel is lower than per module.

Closed-panel factories with full lining and integrated MEP have the same paint, joinery and weld zones as a volumetric factory in miniature. Open-panel factories that only deliver the framed structural shell skip the paint and finish zones but retain heavy welding and joinery. The 6 ACH general baseline is the same; the difference is in the smaller absolute zone size and the higher number of panels per shift, which drives a higher count of cross-zone transfers and therefore a denser supply trunk grid.

Bathroom pod factories — wet trades plus tile dust

Bathroom pod manufacturing is a specialist sub-segment of Australian prefab. Nuvolab in Melbourne is the integrated leader, with bathroom pods produced for the Hickory and Modscape platforms among others. Bathroom Manufacturers Australia and OK Pods cover the merchant market. The factory environment is materially different from a generic volumetric line because of the wet trades content — tiling, grouting, silicone application, plumbing finish — and the silica and cementitious dust generated during tile cutting and grout mixing.

The bathroom pod factory ventilation specification:

• Tile cutting and grouting — 6 ACH with H-class HEPA on local exhaust. Silica is the controlling hazard. Source extraction at every tile saw and bench grouting station, ducted to a HEPA-filtered baghouse. Workplace exposure standards for respirable crystalline silica are tight and trending tighter — design for headroom.
• Plumbing finish and waterproofing — 4–6 ACH with VOC capture at adhesive stations. Waterproofing membranes and adhesives release VOCs during application. Local exhaust hoods over membrane application benches, ducted to an activated carbon scrubber.
• Pod assembly — 4 ACH general. Standard galvanised duct, balanced supply and return.
• Silicone and sealant application — 4 ACH plus local extraction. Solvent-borne sealants release VOCs. Local extraction at every sealant bench.
• Final inspection and packaging — 4 ACH with NC-40. Tight noise control, balanced thermal.

The duct material in a bathroom pod factory needs more thought than in a dry assembly factory. Stainless steel on the wet trades zones and on any duct that runs through humid air is the SBKJ recommendation. Galvanised on the rest of the factory. The SBAL-V auto duct line takes both coil types and produces both materials on the same machine with a coil change, which is why we suggest the dual-capability configuration for any modular or prefab shop that includes pod manufacturing.

Facade panel prefabrication — composite lay-down plus VOC capture

Facade prefabrication is a distinct industrial segment within the Australian prefab industry. Inhabit Group in Sydney and Auckland is the dominant player on engineered facade prefab, with Permasteelisa Australia covering the premium curtain-wall and unitised facade segment. The factory environment differs from a volumetric module factory because of the dominance of composite materials, structural silicone, polyurethane adhesives and metal cladding finishes — all of which release VOCs and isocyanates during application and curing.

The facade prefab factory ventilation specification:

• Composite lay-down — 8–10 ACH with full VOC capture. Composite panel adhesives and resins release VOCs and isocyanates during open application and curing. Local exhaust ventilation at the lay-down bench with capture velocity 0.5–0.75 m/s, ducted to dedicated activated carbon scrubbers — never combined with general factory return.
• Structural silicone glazing — 6 ACH plus bench-level extraction. Solvent-borne silicone systems release VOCs. Bench-level slot extraction over every glazing station, ducted to a carbon scrubber.
• Metal cladding cutting and forming — 4–6 ACH plus LEV at brakes and shears. Dust and metal fines from aluminium and steel cladding work. LEV ducted to a baghouse.
• Spray finish and PVDF paint — 8–10 ACH with NFPA 33 booth. Same paint zone specification as a volumetric factory.
• Quality inspection and packaging — 4 ACH with NC-40.

The combination of composite VOC capture and NFPA 33 paint booth means a facade prefab factory has the highest total exhaust airflow per square metre of any Australian prefab segment. The duct count is high, the cross-sections are large, and the material specification leans heavily toward stainless on the chemically aggressive zones.

Paint shop ventilation — NFPA 33 plus AS 1668

The paint shop is the highest-risk ventilation zone in any modular or prefab construction factory. The combination of flammable solvent vapour, atomised paint particulate, electrical ignition sources and human operators makes this zone the place where ventilation engineering is regulated to the nearest fraction of a metre per second.

NFPA 33 is adopted in Australia as the de facto standard for spray booth ventilation design, supplementing AS 1668. The headline requirements:

• Booth face velocity. 100 fpm (0.5 m/s) for downdraft booths, 150 fpm (0.75 m/s) for crossdraft booths. Measured at the booth face with the booth empty.
• Air change rate. 8–10 ACH in the immediate paint zone and the booth surrounds, calculated against the booth volume plus the operator approach zone.
• Make-up air. Tempered, filtered make-up air at the same volume as booth exhaust, introduced above the booth at low velocity (0.25 m/s maximum) to avoid disturbing the booth face flow.
• Intrinsic safety. Fans, motors and switches inside the booth and within 3 m of the booth face rated for the relevant hazardous area zone classification (Zone 1 or Zone 2 depending on the booth type and the paint flash point).
• Exhaust treatment. Cartridge or water-wash particulate scrubbing before activated carbon for VOCs, before atmospheric discharge through a stack at least 3 m above the highest roof point within 15 m.

The duct between the booth and the exhaust scrubbing is the most demanding piece of metalwork in the entire factory. SBKJ's recommendation for the booth exhaust trunk is 316L stainless steel manufactured on the SBAL-V auto duct line with the stainless coil option, full TDF flange connection (no rivets through the duct wall, which compromise solvent containment), and continuously welded longitudinal seams on the duct downstream of the booth wet wash. The supply duct can be galvanised on the make-up air side because it is upstream of the contaminant.

Welding fume capture — source extraction across robotic and manual stations

Welding is the single largest contributor to fume load in a modular construction factory. Steel-framed volumetric modules are welded continuously across multiple stations, and the fume profile includes manganese, hexavalent chromium (on stainless welding), iron oxide, ozone and nitrogen oxides depending on the consumable and process. AS 3853 is the regulatory backbone in Australia. Workplace exposure standards for welding fume have tightened significantly over the past decade — the days of relying on general ventilation to handle weld fume are over for any factory operating at scale.

The SBKJ engineering recommendation for weld fume capture in a modular factory:

• Robotic welding cells. Hood extraction directly above the cell with capture velocity 0.5 m/s at the arc, ducted in galvanised rigid duct (no flexible) to a central cartridge collector. AS 3853 fume class W3 filter media. Total filtered air re-circulated to the factory or discharged through a stack depending on the local regulatory pathway.
• Manual welding stations. Flexible source extraction arms — one per welder — with capture velocity 0.5 m/s at 300 mm from the arc. Articulated arm geometry to allow positioning by the welder. Ducted to the same central collector as the robotic cells, or to a separate collector if the cell count justifies it.
• Tack welding and minor weld stations. Bench-level slot extraction at the tack welding bench, ducted into the main collector ductwork.
• Cartridge collector. Sized for the total weld station count plus 25 per cent contingency, with pulse-jet self-cleaning, automatic dust hopper discharge, and intrinsically safe construction if the welding includes any aluminium or magnesium content. AS 3853 W3 filter media.

The duct between the source capture and the cartridge collector is structural duct in spirit — it runs at higher static pressure than supply duct (3–6 kPa typical), it carries abrasive particulate, and any leak is a code violation rather than a comfort issue. We specify it as P3 class duct to AS 4254 with continuously welded longitudinal seams, manufactured on the SBAL-V line in a heavier gauge than the supply duct.

Adhesive lay-down and composite VOC capture

Composite facade manufacturing, structural insulated panel (SIP) production, and integrated bathroom pod construction all involve adhesive lay-down on benches where the adhesive is open to atmosphere during application and the early phase of curing. The VOC profile depends on the adhesive system — polyurethanes release isocyanates, methacrylates release MMA, epoxies release amines — and the local exhaust ventilation needs to be specified against the most hazardous component, not the average.

The capture geometry for adhesive lay-down is the controlling design parameter:

• Side-draft slot. For open-bench lay-down, a slot hood along one or both long edges of the bench with capture velocity 0.5–0.75 m/s at the bench surface. Slot dimensions 100 mm by the full bench length.
• Downdraft bench. For small-part work, a perforated stainless top with the bench acting as a single plenum. Face velocity 0.5 m/s across the top surface.
• Push-pull system. For very large benches, a low-velocity push jet on one side and an exhaust slot on the opposite side, generating a curtain of air that sweeps VOCs into the exhaust. This is the geometry used on the largest composite lay-down benches.

The exhaust duct runs in dedicated stainless trunks to an activated carbon scrubber. This duct is never combined with the general factory return — the VOC loading is too high and the cross-contamination risk to other zones is unacceptable. SBKJ supplies the stainless duct stock on the SBAL-V line with the stainless coil option.

Concrete batching and on-floor wet trades — silica control

Where a modular factory includes on-floor wet trades — concrete batching for in-line slab pours on modular concrete cores, screed pouring for floor toppings, or precast element finishing — silica is the controlling hazard. The Australian respirable crystalline silica workplace exposure standard is 0.05 mg/m³ as an 8-hour time-weighted average, and the National Construction Code and Safe Work Australia guidance is unambiguous about the requirement for engineering controls before respiratory protection.

The HVAC strategy:

• Batching enclosure. Full enclosure around the batch plant with negative pressure containment, exhaust ducted to a baghouse with H-class HEPA on the discharge.
• Pouring and finishing. Local exhaust ventilation at the pour point, capture velocity 0.5 m/s, ducted to the same baghouse.
• Cutting and grinding of cured product. Wet cutting where geometrically possible, with shroud extraction at every saw and grinder. Where wet cutting is not feasible, dry cutting with shroud extraction ducted to a HEPA-filtered baghouse.
• General factory air. 6 ACH baseline with displacement ventilation pattern — supply low, exhaust high — to keep silica-laden air out of the breathing zone.

This zone is where stainless duct earns its premium. Galvanised duct exposed to humid air with cementitious dust loading degrades faster than the duct life otherwise warrants. We specify stainless on every duct downstream of the batching enclosure and on every duct that runs through the wet trades zone.

Bathroom pod factory — tile dust, grout and condensate

The bathroom pod factory is the most demanding HVAC environment in the Australian modular sector because it concentrates wet trades, silica generation, VOC exposure and humid air handling into a single building. Nuvolab in Melbourne, Bathroom Manufacturers Australia and OK Pods all operate at scale and have refined the ventilation envelope over multiple factory iterations.

The ventilation specification on top of the wet-trades zoning detailed above:

• Tile cutting bay. Dedicated enclosure with negative pressure containment, wet cutting where possible, H-class HEPA on extraction discharge. Stainless duct throughout.
• Grout mixing and application. Local exhaust at the mixing station, ducted to a baghouse. Application zone at 6 ACH with displacement supply.
• Plumbing finish. 4 ACH with VOC capture at the silicone and waterproofing benches.
• Condensate management. Every duct trunk in the wet trades zone is designed with continuous fall back to a condensate drain at the low point of the trunk. Stainless duct, sealed seams, accessible clean-out doors at 6 m intervals.
• Final inspection. 4 ACH with NC-40 acoustic, balanced thermal control, no airflow turbulence at the inspection bench.

The duct in this factory is more than half stainless steel by weight in our typical specification. The SBAL-V line with the stainless coil option produces both grades — the contractor swaps coil at the line, recalibrates the form rolls (which the SBKJ line does automatically on a new coil entry), and runs stainless trunk against the same drawings as the galvanised on the rest of the factory.

Major Australian modular projects and the factories behind them

The visible end of the Australian modular construction industry is the projects on the ground. The factories that built them are the same factories that need the HVAC infrastructure described above. A short tour of recent reference projects:

• 36 Geelong (Sense of Space). 14-storey residential building delivered as volumetric modules from the Sense of Space factory in Brisbane, transported to Geelong and craned onto a podium. The tallest modular building in the southern hemisphere at the time of completion. The Sense of Space factory runs a high-throughput volumetric line with paint, joinery, MEP and finish zones all under one roof.
• La Trobe University Bundoora modular accommodation. Multi-storey student accommodation delivered as volumetric modules into the La Trobe Bundoora campus, used to expand on-campus housing without a multi-year traditional construction program.
• NSW Land and Housing Corporation social housing modular program. A multi-year program of social housing delivery using volumetric modular product, with Strongbuild as a lead supplier into the program at peak. The Strongbuild Sydney factory built dwellings at a cadence that would have been impossible on traditional contracting.
• Brisbane Airport modular hotel tower. A modular hotel tower delivered into the Brisbane Airport precinct as a stack of volumetric modules. A landmark project for Australian high-rise modular and a reference for the volumetric format at scale.
• Western Australia mining accommodation camps. Fleetwood Building Solutions (and its previous Searipple operation in Karratha) has supplied accommodation modules to BHP, Rio Tinto and Fortescue Metals Group sites across the Pilbara and Goldfields. Mining camp accommodation has been the volume backbone of Australian modular for two decades.
• Hickory Sync and World of Sync social housing. Hickory Group's Sync platform in Melbourne, including the World of Sync social housing program, delivers volumetric modular tower modules into central business district and inner-suburban sites. The Hickory Brooklyn factory in Melbourne runs the production end.
• Modscape commercial and residential. Modscape in Melbourne delivers premium custom modular into commercial, residential and specialist markets, with a factory that has progressively moved upmarket on quality and finish.
• Inhabit Group facade prefab. Inhabit Group operates facade prefabrication factories across Sydney and Auckland, delivering unitised curtain wall and engineered facade systems into Australian and New Zealand high-rise.

Each of these factories runs an HVAC envelope that meets the specifications described in this guide. The duct inside the factory walls is in many cases manufactured in-house — modular builders at scale operate their own duct shops, both for the factory's own infrastructure and for the duct that ends up inside the modules they ship. This is the segment where SBKJ duct machinery has direct application.

Acoustic targets — NC-50 factory, NC-40 office

Acoustic comfort is a real constraint in a modular factory at scale. The combination of compressed air tools, robotic welding, joinery saws, panel handling cranes and mechanical ventilation can push background sound pressure levels into the 80 dB(A) territory if the HVAC system is not designed against an acoustic target. The Australian baseline:

• Main factory hall — NC-50. The HVAC contribution to total noise should be below NC-50 when measured under no-process conditions. This requires duct silencers on the main supply and return trunks, lined plenums at the fan discharge, and acoustic louvres on external intake and discharge.
• Office and amenities — NC-40. Tighter target for office areas, training rooms and meeting spaces. Lined duct branches, terminal-level silencers where the duct enters the office zone, and acoustic dampers on the office return.
• Inspection and finish bays — NC-40. Where the work content requires concentration and inspection, the NC-40 target applies.

Duct silencer specification follows AS 1668 acoustic clauses and the broader ASHRAE acoustic guidance. The duct itself contributes to acoustic performance — lined duct attenuates more than bare duct, and SBKJ supplies duct manufactured on the SBAL-V line with internal lining attached on the line or as a post-form operation depending on the contractor's preference.

Smoke management — AS 1668.1 plus AS 4391 for the larger factories

A modular construction factory above the NCC area and storey thresholds requires a smoke management system. AS 1668.1 governs the design of smoke control ventilation, AS 4391 governs the design of smoke management systems specifically, and the NCC sets the trigger thresholds. A 6,000 square metre volumetric modular factory is well above the typical trigger, and smoke management is mandatory.

The strategy in a high-bay modular factory:

• Smoke exhaust at high level. Roof-mounted smoke exhaust fans rated for 200°C / 2 hours, with smoke exhaust duct manufactured to AS 4254 P3 class with fire-rated coatings or insulation where the duct passes through fire compartments.
• Make-up air at low level. Low-level intake doors or louvres opening on fire alarm activation, providing make-up air to replace the smoke exhaust without disturbing the smoke layer above.
• Smoke detection and zone control. Multi-zone smoke detection with zone-specific exhaust fan activation. AS 1668.1 zoning rules apply.
• Smoke curtains. Automatic smoke curtains at zone boundaries inside the factory to contain smoke spread, particularly between paint zone and adjacent zones.

The smoke exhaust duct is the most onerous duct specification in the factory after the paint booth exhaust. We typically specify it as P3 class to AS 4254, in heavier gauge than the comfort duct, with continuously welded longitudinal seams on the SBAL-V line. The fire-rated coating or insulation is applied off-line as a post-form operation.

Duct material selection — galvanised, stainless, and where to draw the line

Material selection across a modular factory is a balance between code compliance, durability and capital cost. The SBKJ engineering rule of thumb:

• Galvanised steel to AS 4254. General supply and return on coil receiving, framing, joinery, MEP rough-in, internal lining, glazing, finish (away from paint), packaging and despatch. 0.5 mm to 1.0 mm gauge depending on duct size and pressure class. This is 60–70 per cent of the duct in a typical modular factory by weight.
• Stainless steel (304 or 316L) to AS 4254. Paint zone exhaust, composite lay-down exhaust, bathroom pod wet trades, concrete batching exhaust, and any duct downstream of a wet scrubber. 304 is standard, 316L where chloride exposure is elevated.
• Aluminium. Specialist applications only — typically not in a modular construction factory unless there is a specific corrosion or weight rationale.

The SBAL-V auto duct line at SBKJ takes both galvanised and stainless coil with a coil change at the entry. The form rolls are designed to handle both materials with a recalibration cycle that the PLC handles automatically. The contractor can run a galvanised shift in the morning and a stainless shift in the afternoon without mechanical changeover beyond the coil swap. This dual-capability is the single most important configuration choice for a duct shop serving a modular factory, because it eliminates the need for two separate auto lines or for an outsourced stainless supply chain.

SBKJ machine configuration for a modular construction duct shop

For a contractor or builder running an internal duct shop to supply a modular construction factory, the SBKJ baseline configuration:

• SBAL-V auto duct line. The primary branch duct line. Galvanised and stainless coil capability. Forms rectangular duct from 200 mm to 1,500 mm wide on a single pass with TDF flange edges integrated. Average single-shift output 800–1,200 metres of branch duct depending on the size mix. Full SBAL-V specification.
• SBTF-1602 main trunk forming line. The main supply and return trunk line. Forms rectangular duct up to 1,600 mm wide on a single pass with TDF flange edges integrated, in heavier gauge than the SBAL-V output. Used for the main supply and return trunks that distribute air to the zonal branches.
• SBKJ Coilmaster spiral former (optional). Round duct for bathroom pod extract risers, kitchen extract risers, and any application where round duct is preferred over rectangular for pressure drop or aesthetic reasons.
• SBKJ Plasma cutter (optional). CNC plasma cutting of duct fittings, transitions and special-shape components. Integrates with the SBAL-V for fitting blanks.
• SBKJ TDF flange former. Standalone TDF flange forming for joining duct sections in the field. Standard 25 mm and 30 mm flange depths.

This configuration covers the full duct production envelope of a modular construction factory in-house. The capital cost is in the range of AUD 350K to AUD 600K depending on the exact line specification and the spare-parts and training package. The total cost of ownership over a 15-year horizon, accounting for the duct production it supports, is well inside the cost of outsourced duct supply for a factory of any scale. See our pricing and lead time guide for current ranges.

Procurement and commissioning — the modular factory build sequence

A new modular construction factory in Australia typically follows a 9–18 month build sequence from concept to first module off the line. The HVAC ductwork procurement and commissioning sits inside that sequence:

1. Months 0–3 — Concept and DfMA design. Factory layout, zone definition, work content per station. Ventilation rate calculation to AS 1668.2 by the consulting engineer.
2. Months 3–6 — Detailed mechanical design. Duct layout, sizing, pressure class assignment, material specification. Tender documentation issued.
3. Months 6–9 — Duct machinery procurement. If the builder is running an in-house duct shop, this is the window for SBKJ machine procurement. SBAL-V and SBTF-1602 lead time is 8–14 weeks from order to factory acceptance test. See our HVAC duct machine buyer's checklist for the procurement framework.
4. Months 9–12 — Duct fabrication. In-house production of factory supply, return, exhaust and smoke management duct. Parallel with mechanical contractor installation of plant.
5. Months 12–15 — Installation and commissioning. Duct hung and connected, plant connected and tested, ventilation balanced against AS 1668.2 design intent, smoke management commissioned against AS 4391.
6. Months 15–18 — Production trials and first module. Trial production runs on the new factory floor, HVAC system tuned against the actual contaminant profile of the trial production, certification and handover.

The duct machinery procurement window is the leverage point. A contractor who orders an SBKJ auto duct line at month 6 has the line commissioned by month 9 and can fabricate the factory's own duct in time for installation at month 12. A contractor who waits until month 9 to consider the duct production approach is forced into outsourced supply with a 6–10 week lead time on each batch, which is typically more expensive on landed cost and constrains the design flexibility on duct fittings.

Indoor environmental quality — beyond the code

The Australian modular construction sector has progressively moved up the indoor environmental quality curve as the product moves into higher-spec residential, commercial and accommodation markets. The duct system inside the modules — the duct that the customer's tenants will breathe through for the next 30 years — is part of that quality story. Modular and prefab builders increasingly specify:

• Low-VOC duct sealants and gaskets. The duct inside a module ships sealed, and any sealant outgassing happens inside the closed module environment. Low-VOC specification reduces tenant exposure on first occupation.
• Anti-microbial duct coatings. Particularly on bathroom and kitchen exhaust duct, anti-microbial coatings reduce the biofilm and mould risk in the duct life. Optional with SBKJ duct on request.
• HEPA-ready filter housings. Module duct that ends in a unit terminal with a HEPA-ready housing allows the building operator to upgrade filtration in response to local air quality events without re-engineering the duct.
• Acoustic-rated duct. Lined or double-skin duct on the duct sections nearest to bedrooms and quiet zones, attenuating fan noise to NC-30 inside the module.

Each of these specifications is supported by SBKJ duct manufactured on the SBAL-V line. The line takes pre-treated coil for anti-microbial coatings, accommodates the heavier gauge required for acoustic-rated duct, and forms duct that meets P1 leakage class for the in-module supply branches.

Energy and decarbonisation — the modular factory grid story

The Australian modular construction sector is moving in step with the broader construction decarbonisation agenda. The HVAC system in a modular factory is one of the larger consumers of grid energy on the site, and the procurement and design decisions made on the HVAC plant have a long-tail consequence on factory operating cost and emissions intensity.

The decarbonisation playbook our engineers walk through with modular and prefab builders:

• Heat recovery on exhaust. The paint zone, composite lay-down zone and welding fume exhaust are high-temperature exhaust streams. A heat recovery exchanger on the exhaust transfers thermal energy to the make-up air supply, reducing the heating load on the air handler. Typical recovery 60–75 per cent of available sensible heat.
• Variable speed drives on every fan. Fixed-speed fan operation is the largest single waste of HVAC energy in a factory. Variable speed drive on every supply, return and exhaust fan, with PLC control linked to zone occupancy and contaminant load, is the baseline.
• Demand-controlled ventilation. CO₂ sensors in occupied zones, VOC sensors in chemical zones, and particulate sensors in dust-generating zones drive the supply and exhaust airflow in real time. The general baseline runs at the AS 1668.2 minimum during low-occupancy periods and ramps up to design when the zone is fully active.
• Rooftop solar. A 6,000 square metre factory roof is a 1.5 MW rooftop solar opportunity. The solar generation profile aligns well with the factory daytime HVAC load.
• Electrified plant. Heat pump rather than gas boiler on the air handler heating coil, removing the fossil fuel input from the HVAC system. Australian electricity grids are decarbonising faster than the national gas network is, and the operating emissions of a heat pump trend down over the factory life.

The duct design contributes to the decarbonisation outcome by minimising pressure drop and leakage. SBKJ duct manufactured to P1 supply class and P3 exhaust class meets AS 4254 leakage targets, and the integrated TDF flange on the SBAL-V line minimises field-applied sealant — which is typically the largest contributor to long-term duct leakage.

Common procurement mistakes in modular factory HVAC

The SBKJ engineering team has commissioned duct machinery into modular construction factories across Australia for the past decade. The recurring procurement mistakes:

• Treating the factory as a generic shed. A modular factory is a precision manufacturing plant, not a warehouse. AS 1668.2 dilution ventilation is not sufficient for paint, weld and composite zones. Specify zonal extraction.
• Underspecifying paint zone exhaust. NFPA 33 face velocity and ACH are non-negotiable. Cutting corners here is a fire risk and a code violation.
• Mixing weld fume into general exhaust. Weld fume needs source capture and dedicated ductwork to a cartridge collector. Mixing it into the general return propagates manganese and hex-chromium across the whole factory.
• Galvanised duct in wet zones. Bathroom pod wet trades, concrete batching exhaust, paint booth exhaust — all need stainless. Galvanised in these zones is a 5-year duct life rather than a 25-year duct life.
• Outsourced duct supply during factory commissioning. Outsourced duct supply during the duct installation window typically costs 30–50 per cent more on landed cost than in-house production on an SBKJ auto duct line. The capital cost of the auto duct line is paid back inside the first factory build.
• No spare-parts continuity plan. The duct machinery is a 15-year asset. Without a 10-year parts continuity guarantee from the supplier, the duct shop is one PLC fault away from a six-month downtime. SBKJ commits in writing to 10-year parts continuity on every machine.

Case study perspective — what a 8,000 sqm volumetric factory looks like in duct terms

To make the numbers concrete, here is a worked example of a hypothetical 8,000 square metre volumetric modular factory configured along the lines of the Sense of Space, Hickory Sync or Modscape product. The numbers are illustrative rather than project-specific but they sit comfortably in the band of what our engineers see across the Australian sector.

The factory contains 16 ventilation zones across the work content described earlier. Total installed supply air at design is approximately 360,000 m³/h. Total installed exhaust air at design is approximately 220,000 m³/h, of which 60,000 m³/h is dedicated paint zone exhaust, 40,000 m³/h is dedicated weld fume extraction to a central cartridge collector, 15,000 m³/h is composite and adhesive VOC capture, and 105,000 m³/h is general factory return. The acoustic target is NC-50 on the main hall and NC-40 on the office mezzanine, and the smoke management system is sized for a 6 metre clear smoke layer at 200°C.

The duct stock to deliver that installation breaks down approximately as follows: 4,200 linear metres of rectangular supply duct between 200 mm and 1,200 mm in galvanised steel, 1,800 linear metres of rectangular return duct between 400 mm and 1,800 mm in galvanised, 1,400 linear metres of rectangular exhaust duct in stainless (paint, composite and wet trades), 600 linear metres of stainless welded duct on the paint booth and cartridge collector trunks, 350 linear metres of round spiral duct between 200 mm and 600 mm for pod and kitchen extract risers, and a balance of fittings, transitions and dampers. Total duct weight comes in at around 95 tonnes.

Producing that duct stock on an SBKJ SBAL-V plus SBTF-1602 plus Coilmaster combination is a five to seven week task with a single-shift dedicated crew. Outsourcing it on the open market is typically a 14–22 week supply chain with significant scheduling risk against the factory commissioning date. The in-house production option is faster, lower landed cost, and gives the builder full flexibility on fitting geometry, change orders and corrections during installation. The SBKJ line is paid back inside the first factory build.

Operator and maintainer training — the people side

The HVAC ductwork is a 25-year asset and the duct machinery that produces it is a 15-year asset. The people who operate both need training that sticks, and SBKJ structures the training in a way that aligns with how Australian modular and prefab builders actually staff their duct shops.

• SBAL-V auto duct line operator training. 16 hours over two days on the production floor. Coil loading, line setup, PLC interaction, quality check at the discharge, common fault diagnosis and recovery. English language standard, with translated documentation available on request.
• Maintenance training. 8 hours on the second day. Preventive maintenance schedule, lubrication points, hydraulic system inspection, tooling regrind, sensor replacement. Sets up the duct shop for self-sufficiency over the SBAL-V's first 5 years of life.
• Commissioning report. Written report signed by the SBKJ commissioning engineer, listing every test run, every measured output and every adjustment. Becomes the baseline reference document for the duct shop's quality system.
• Factory HVAC commissioning support. SBKJ engineers are available on a paid consulting basis to support the factory HVAC commissioning against AS 1668.2 design intent. This is in addition to the duct machinery commissioning and is typically engaged by builders who do not have a deep in-house HVAC engineering function.

How SBKJ supports modular and prefab construction factories

SBKJ's product line is purpose-built for HVAC duct contractors and the in-house duct shops of modular and prefab builders. The capabilities relevant to a modular construction factory:

• SBAL-V auto duct line. The workhorse rectangular duct line. Galvanised and stainless coil, 200 mm to 1,500 mm width, P1 to P3 pressure class, integrated TDF flange. Average single-shift output 800–1,200 metres.
• SBTF-1602 main trunk forming line. Main supply and return trunks up to 1,600 mm width, in heavier gauge than the SBAL-V output. The trunk line for the largest cross-sections in a high-bay modular factory.
• SBKJ Coilmaster spiral former. Round duct for bathroom and kitchen extract risers in modular and pod factories.
• SBKJ Plasma cutter. CNC duct fitting and transition blanks.
• SBKJ TDF flange former. Field flange forming for joining duct sections.
• Australia office in Box Hill North, Victoria. English-speaking after-sales, on-shore spare parts inventory for SBAL-V and SBTF lines, engineer-led commissioning support.
• 10-year parts continuity guarantee. In writing on every order.
• Engineer-led 12-hour reply. All technical questions answered by an SBKJ mechanical engineer within 12 hours, not by a salesperson.

Talk to an SBKJ engineer about your modular factory duct shop →

FAQ

What air change rate is required in a volumetric modular factory paint zone?

For paint zones and spray booths inside a volumetric modular or panelised prefab factory, design for 8–10 air changes per hour (ACH) with full local exhaust at the booth face, NFPA 33 compliant booth ventilation, and AS 1668.2 cross-referenced make-up air. General assembly bays away from spray operations run at 4–6 ACH.

Which Australian codes apply to a prefab construction factory HVAC system?

The primary codes are the National Construction Code (NCC) Volume One Section F (mechanical ventilation), AS 1668.1 fire and smoke control, AS 1668.2 mechanical ventilation, AS 4254 ductwork specification, AS 4391 smoke management, AS 3853 welding, AS 3600 concrete and AS 4100 steel for the factory structure. prefabAUS and the MBA Modular Building Council provide industry guidance on top.

Does a bathroom pod factory need stainless duct?

For the wet trades zone of a bathroom pod factory — tiling, grouting, silicone application — stainless steel duct is recommended on supply and return because of constant exposure to airborne silica, cementitious dust and humid air. For the assembly, joinery and packaging zones of the same factory, galvanised duct is industry standard and meets AS 4254. SBKJ supplies both grades on the same SBAL-V auto duct line with a coil change.

What is DfMA and how does it change factory ventilation design?

Design for Manufacture and Assembly (DfMA) designs the building specifically for factory production rather than site construction. In ventilation terms it means high-bay factories with predictable, repeated work zones — paint, weld, assembly, joinery, packaging — that can be ducted as discrete zones rather than as a single open hall. This favours zonal supply and exhaust over diffused whole-building ventilation, and rewards trunk-and-branch duct layouts produced on auto duct lines such as the SBKJ SBTF-1602.

Which SBKJ machine configuration suits a modular construction factory?

For a typical Australian modular or prefab construction factory producing duct internally for its own facility (and often for the modules it builds), the standard SBKJ configuration is the SBAL-V auto duct line with galvanised plus optional stainless coil capability, paired with the SBTF-1602 main trunk forming line for supply trunks above 1,200 mm. Bathroom pod and bathroom module factories often add an SBTF Coilmaster for round duct used in pod extract risers.