Key takeaways
- Prefab supply should be administered as a separate procurement stream with its own order documentation, approvals and delivery milestones, not folded into the structural subcontract.
- Design freeze is a commercial event: once the order is placed, any change becomes a variation to a factory programme rather than a site instruction you can absorb.
- Lead times are consumed by approval cycles, so late return of shop drawings or engineering certification is the most common cause of a late delivery that is then blamed on the supplier.
- Retention and payment terms on prefab packages need to be checked against the security of payment requirements, particularly where retention money is held by a head contractor.
- Supplier insolvency is a live risk on long-lead prefab orders, so you need to know what stage your deposit has reached and what you can recover if the supplier enters voluntary administration.
Prefabricated and modular supply changes where the risk sits on a residential job. The work that used to be spread across several trades on site is compressed into a factory programme and a delivery date, and the builder’s exposure shifts from supervising labour to administering a supply contract. That is a different skill, and it is the one that usually decides whether the package makes money.
The losses on prefab packages rarely come from the manufacturing itself. They come from an order that was priced against one revision and built against another, from a delivery that arrived before the slab was ready, from a crane that was booked for a day the truck did not turn up, or from a deposit paid to a supplier whose financial position nobody checked. All of those are administration failures, and all of them are visible in the paperwork well before they are visible on site.
This article deals with the project management of prefab supply rather than the methods themselves. It covers how to structure the order, how to control the approvals cycle that eats lead time, how to sequence delivery against the rest of the programme, and how to handle payment, defects and retention so the final account reflects what was actually delivered.
Treat prefab supply as its own procurement stream
The first structural decision is whether the prefab package sits inside an existing subcontract or stands alone. Folding a modular or panelised supply into a carpentry or structural subcontract looks tidy on a trade schedule, but it usually means the order documentation is written by someone whose primary interest is the site labour component, not the factory lead time. The result is a subcontract that describes installation and says almost nothing about the approvals cycle, the delivery window or the inspection hold points.
A separate supply agreement does not need to be complicated. It needs to do four things: identify the frozen design the supplier is pricing, state what the supplier is responsible for designing and certifying, set out the delivery milestone and what has to be true on site for it to be met, and allocate responsibility for defects and tolerances. Everything else is detail that can be negotiated.
It also needs a named owner on your side. On small residential jobs the builder is often the owner, and the practical failure is that the order is placed and then not looked at again until the delivery is due. Assign the package to one person and give them a register they actually update — the same discipline described in managing subcontractors on site in NSW, applied to a supplier who may never set foot on the job.
Freeze the design before the order, not after
Design freeze is a commercial event, not a design milestone. Up to the point the order is placed, a change is a drawing revision and a conversation. After it, a change is a variation to a factory programme: materials may already be cut, a position in the production line may already be booked, and the supplier will price the disruption accordingly. Builders who treat freeze as a formality are the ones who discover that a late window relocation costs more than the window.
Before releasing the order, confirm in writing that the drawings the supplier is pricing match the drawings the certifier and the client have seen. On prefab work the interfaces matter more than the elements: how the panels meet the slab, where the services penetrate, how the roof line resolves, what tolerance the supplier expects the slab to be built to and who pays if it is outside that tolerance. These are the items that generate the arguments later.
Record the freeze date. It anchors the lead time, it anchors the variation position, and it is the first thing anyone asks about when a delivery slips.
Understand what actually consumes lead time
Suppliers quote lead times from different starting points, and the difference matters. Some quote from receipt of order, some from receipt of approved shop drawings, some from receipt of deposit. A supplier quoting from approved drawings has effectively excluded the approval cycle from their commitment, which means any delay in your review is not their problem.
Ask the question directly and get the answer in the order documents. Then work backwards through the approval cycle: shop drawings prepared by the supplier, reviewed by you or your designer, engineering certification issued, any certifier or council input obtained, and the deposit paid. Each of those steps sits between you and the start of manufacture, and each of them is under your control in a way that the factory programme is not.
Late return of shop drawings is the single most common cause of a late prefab delivery that is then blamed on the supplier. It is also the easiest to fix, because it is an internal process problem rather than a supply problem. A dated register with a review turnaround commitment on your side removes most of it.
Administering a prefab order from enquiry to handover
- 1Scope and freezeConfirm the design, tolerances and interfaces the supplier is pricing, and record the date the design is frozen.
- 2Order and depositIssue a purchase order that references the frozen drawings, and pay any deposit against a tax invoice with matching details.
- 3Approvals cycleTrack shop drawing review, engineering certification and any certifier or council input as a dated register item.
- 4Manufacture and inspectionHold points for pre-delivery inspection and any third-party verification the specification requires.
- 5Delivery and installBook the crane, the lay-down area and the trades that follow, and record the condition of each module or panel on arrival.
- 6Defects and close-outLog defects against the supplier, resolve them before final payment, and release retention only when the contract allows.
Sequence delivery against the rest of the programme
A prefab delivery is a heavy vehicle event, not a trade arrival. It needs access, a crane or a hiab, a lay-down area sized for the largest module or the full panel set, and a crew ready to receive and fix. If any of those is missing on the day, the truck either waits at your cost or leaves and the delivery is rescheduled into whatever slot the supplier has next.
Work the delivery date backwards into the programme and identify the predecessor activities that must be complete: footings and slab cured and stripped, set-out verified, services roughed in where they run under or through the prefab elements, scaffolding or crane access established, and the following trades booked for the days after. Then identify the activities that the delivery blocks, because a delayed prefab delivery does not just delay one trade, it pushes the whole wet area of the programme.
On constrained sites, consider whether the delivery can be staged. Splitting a panel set across two deliveries costs more in freight and crane time but can be the difference between a workable site and a shutdown.
Before you release a prefab order
- The frozen drawing set is identified by revision and date.
- Interfaces with footings, slab, services and finishes are documented, not assumed.
- Lead time is stated from order and from approval, not as a single figure.
- Delivery access, crane position and lay-down area are confirmed with the supplier.
- Tolerance and setting-out responsibility is allocated in writing.
- Payment terms, deposit and retention position are consistent with the head contract and the security of payment requirements.
- A named person on site owns the delivery day, not the whole team.
Manage variations to a frozen order
Once the order is placed, every client-initiated change has to be priced twice: once for the change itself and once for the disruption to the factory programme. Builders who only price the first component absorb the second. The way to avoid that is to make the disruption visible in the variation. If the supplier has quoted a rework charge or a rescheduling fee, pass it through with the supplier’s written advice attached.
The same discipline applies to changes that originate on site. If the slab is out of tolerance and the supplier has to modify the panels to fit, that is a variation, and it needs to be documented on the day rather than reconstructed at the final account. The commercial principles here are the same ones covered in quoting residential building jobs in NSW: an undocumented cost is a cost you carry.
Keep a single variation register for the package that shows the instruction date, the supplier’s quotation, the client approval and the effect on the delivery date. The delivery date effect is the part most builders omit, and it is the part that causes the argument at practical completion.
Payment, deposits and retention on prefab packages
Prefab supply usually requires a deposit, often a substantial one, because the supplier is committing materials and factory capacity before any work is visible on your site. That is a legitimate commercial position, but it changes your risk profile. You are paying forward for something you cannot inspect and cannot easily resell.
Check the security of payment position before you agree terms. Where retention money is held by a head contractor, there are specific requirements about how it is held and what records must be kept, and those requirements flow through to how you should be holding retention on your own suppliers. If you are holding retention on a prefab supplier, make sure the contract allows it, that the amount and release trigger are stated, and that you are not holding it in a way that breaches the requirements that apply to your own head contract.
Match every deposit payment to a tax invoice with the correct entity name, and pay into an account in that entity’s name. Deposits paid to a related entity or a personal account are difficult to recover and can complicate your position if the supplier subsequently fails.
The mistake that costs the most. Paying a large deposit against an order that does not identify the frozen drawings, the delivery milestone and the supplier’s legal entity. If the supplier stops trading, you have paid for something you cannot identify, cannot inspect and may not be able to recover.
Supplier insolvency is a real risk on long-lead orders
The longer the lead time, the longer your money is exposed. A supplier that enters voluntary administration is placed under the control of an administrator who takes over the company’s affairs, and from that point the commercial relationship changes: you become a creditor, and your position depends on what you have paid and what has been delivered.
Practical steps you can take before that point. Ask for the supplier’s legal entity name and check it matches the entity on the tax invoice. Keep deposits proportionate to the work actually committed. Where the order value is significant, consider whether staged payments against completed manufacturing milestones are achievable instead of a single large deposit. If the supplier does enter administration, act quickly: confirm in writing what has been manufactured, whether it is identifiable as your order, and where it is held.
This is not a reason to avoid prefab supply. It is a reason to know what stage your money has reached at any point in the order, and to have that information in a form you could produce on short notice.
Worked example: a modular extension in western Sydney
A builder in western Sydney wins a contract for a rear extension using a modular bathroom pod and a panelised wall system. The quote is accepted on a preliminary drawing set, and a deposit is paid within a week to hold a production slot. The builder treats the order as done and returns to the site programme.
Three weeks later the client changes the bathroom layout. The builder issues a variation for the fittings but does not contact the supplier, on the basis that the pod is not yet in production. When the supplier is finally notified, the pod frame has been fabricated to the original layout. The rework is quoted as a variation to the factory order, with a rescheduling fee and a new delivery date that pushes the pod past the point where the tiler and waterproofer were booked.
The cost lands in three places. The rework charge is a direct cost. The rescheduled delivery means the following trades are either paid to stand down or rebooked at short notice. And because the pod arrives later than programmed, the practical completion date moves, which affects the builder’s own position under the head contract.
None of this required the supplier to behave badly. It required the builder to treat a post-freeze change as a site variation when it was in fact a change to a factory programme. The fix is administrative: a freeze date in the order, a single point of contact with the supplier, and a rule that no client change is approved until the supplier has confirmed the effect on manufacture and delivery.
Defects, tolerances and the final account
Prefab defects tend to fall into two categories: damage in transit and installation, and manufacturing defects that only appear once the element is in place. The first is a delivery-day issue and needs to be recorded on arrival, with photographs and a signed delivery docket noting the damage. If it is not recorded on the day, the argument about who caused it is unwinnable.
Tolerance disputes are harder. They usually arise because the supplier built to the tolerance stated in their own documentation while the site was built to a different one. The way to avoid this is to make the interface tolerances explicit in the order, and to verify the relevant site dimensions before manufacture rather than after delivery. If the supplier is responsible for verifying site dimensions, say so in the order. If you are, do it and record the result.
Hold the final payment and any retention until defects are closed out and the supplier has provided whatever certification the contract requires. Releasing retention early to maintain goodwill is a common mistake, and it removes the only leverage you have.
Why this sits inside your CPD, not outside it
Prefab and modular supply is a documentation and programme discipline as much as a construction one. The skills involved — writing an order that pins down scope and interfaces, running an approvals cycle to a deadline, sequencing a delivery against the rest of the programme, and administering payment and retention correctly — are the same skills that apply to every other package on the job, applied to a supplier you rarely see.
If you are working through your CPD for the year, the contract administration and project management areas are where this material sits. The guide to how NSW builder CPD works sets out the categories and the record-keeping expectations, and the PointCPD course catalogue lists the courses that cover procurement, contract administration and site management. Builders looking for the full set of NSW builder CPD courses can start from the PointCPD home page.
For related reading on the site side of the same problem, see the article on getting your team to use the software you paid for, which covers how to keep delivery dates and approvals visible without adding administrative overhead you will not maintain.
Questions builders ask
Who owns the risk if a prefab delivery is late because shop drawings were returned late?
That depends entirely on what the order says about when lead time starts. If the supplier quotes from receipt of approved drawings, the approval cycle is your risk and a late return pushes the delivery date without any breach by the supplier. If the supplier quotes from receipt of order, the approval cycle sits inside their commitment and they carry more of the risk. Get the starting point stated in the order documents rather than assuming it.
Should I hold retention on a prefab supplier?
Only if the contract allows it and you have stated the amount and the release trigger clearly. Retention is your main leverage for closing out defects, so releasing it early to maintain goodwill usually costs more than it saves. Check the requirements that apply to retention money held by a head contractor, because those flow through to how you should be holding retention on your own suppliers.
How do I protect a deposit paid to a prefab supplier?
Pay against a tax invoice in the supplier’s legal entity name, into an account in that same name, and keep the amount proportionate to the work actually committed. Where the order value is significant, negotiate staged payments against completed manufacturing milestones rather than one large deposit. If the supplier enters voluntary administration, your position as a creditor depends on what you have paid and what has been delivered, so keep records that identify your order specifically.
What should be recorded when a prefab delivery arrives damaged?
Note the damage on the delivery docket before the driver leaves, photograph it, and notify the supplier in writing the same day. Damage that is not recorded on arrival becomes a dispute about cause, and those disputes are effectively unwinnable once the truck has gone. Keep the photographs with the delivery docket in the same file as the order and the variation register.
Can I change the design after the order is placed?
You can, but it is a variation to a factory programme rather than a site instruction. The supplier may have cut materials or booked production capacity, and they will price the disruption as well as the change itself. The practical rule is that no client change is approved until the supplier has confirmed in writing what it does to manufacture and the delivery date, and that confirmation goes into the variation register.
How do I verify site dimensions before prefab manufacture?
Decide in the order who is responsible for verifying them, and record the result either way. If the supplier is verifying, give them access and a date. If you are verifying, do it before manufacture starts and keep the measurements with the order documents. Most tolerance disputes come from the supplier building to their documented tolerance while the site was built to a different one, and the only defence is a written record of what was measured and when.
Sources
- Voluntary administration · ASIC
- Flood risk management manual · NSW Government
- Modern methods of construction · NSW Department of Planning, Housing and Infrastructure
- Retention money held by head contractors · NSW Government
Published 31 July 2026. General information for builders, not legal, financial or engineering advice for a specific job. Check current requirements with the relevant regulator or standard before relying on them.
