Key takeaways
- A multi-unit job does not simply multiply the economics of a single house, because cash, overheads and risk each change shape as the number of dwellings grows.
- Cash flow is usually the first thing to fail on a medium-density project, because material and labour are paid out long before the progress claims for each unit come in.
- Overheads such as site establishment, supervision and approvals are spread across the units, so the margin depends on how completely the job is staged and kept moving.
- Risk concentrates on a multi-unit site, which means one delay, one failed inspection or one defaulting buyer can reach every unit at once.
- Test the feasibility of a project against a stressed version of its cash flow and its program before signing, not against the best case the developer has drawn.
A builder who has run a dozen single houses may look at a townhouse scheme and see a simple extension of the same work. The footings are the same, the framing is the same, and the trades are the same people. Multiply the house by the number of dwellings and the price, the timeline and the profit should follow. That view is comfortable, and it is wrong in ways that cost real money.
Medium-density work changes the economics because several dwellings now share one site, one crew, one approval and one bank account. The margin on a single house is largely the difference between the price and the cost of that house. On a multi-unit job the margin is also shaped by how the cash moves between the units, how the overheads are spread, and how much of the project depends on one outcome. Each of those behaves differently as the number of dwellings rises.
This article sets out those mechanics for a licensed builder who is considering a project of this kind. It does not cover the individual cost drivers of a single house, which are dealt with in the cost drivers article, and it does not cover knock-down and rebuild projects, which have their own arithmetic. The focus here is on what changes when the job gets bigger, and what a builder should test before committing.
Why a bigger job is not just more of the same job
Scale does two things to a building project. It spreads fixed costs over more units, which helps the margin, and it multiplies the number of points at which something can go wrong, which hurts it. Early in a project the first effect is easy to see and the second is easy to ignore. The builder who quotes a scheme on the strength of the first effect alone has usually not tested the second.
The scale effects are real. Site establishment, the fencing, the amenities, the temporary power, the skip and the site supervisor are the same whether one dwelling or several is under construction. A crew that is well organised can carry the framing or the fit-out across several identical units with less waste than a series of separate houses. Bulk purchasing of common items such as windows, doors and fittings can lower the unit cost, and repetition helps the subcontractors, who learn the detail and work faster.
The difficulty is that the same scale brings the complications along with it. Each unit has its own inspections, its own variations and its own buyer. A problem with the drainage on one unit can hold up the slab on the next, and a delay in one approval can stop the whole program. The money is no longer tied up in one house. It is tied up in several houses that are all waiting on the same few things.
Where the margin actually sits on a multi-unit job
On a single house the margin is mostly the difference between a fixed price and a known cost. On a multi-unit scheme it is usually made up of three pieces: the margin on the build itself, the recovery of the overheads that sit above the units, and the value that the project creates from the way it is staged. The first is the familiar one. The second and third are where the scheme succeeds or fails.
Recovering overheads means the price must carry the cost of the site team, the supervision, the insurance, the finance and the time spent on approvals, not just the materials and labour in each unit. If the price is built up from the unit cost alone, the overheads come out of the margin, and the margin is often thinner than the builder expects. Work out the overhead cost of the whole project first, then decide how it is spread across the units.
Staging is the third piece. A scheme that keeps the same crew moving from one unit to the next, with the materials arriving on time, earns more than the same scheme run in fits and starts. Idle time is the enemy of margin on a multi-unit job, because the crew, the plant and the finance cost continue while nothing is being built.
Rider Levett Bucknall publishes construction market updates, and the June update reported through The Urban Developer is a reminder that input costs can move with events that are well beyond the builder’s control. A feasibility study that assumes today’s material prices will hold for the whole build is not a study. It is a hope, and the builder should price the risk of a movement rather than ignore it.
Cash flow: the gap between paying out and getting paid
Cash flow is the first thing to fail on most medium-density projects, and it is the least visible on the plan. The builder pays for materials, labour and subcontractors as the work happens. The money comes back in stages, through progress claims, deposits, settlements or a construction finance draw, and the timing of those receipts often lags the spending by a long way. On a single house the gap is manageable. On a scheme with several units it can grow until the bank account is empty while the buildings are half finished.
The gap is driven by the payment terms in each contract and by how the units are sold or financed. A scheme where the buyers settle on completion has a long period in which the builder carries the full cost of every unit. A scheme with a construction loan may draw funds only against milestones the bank has approved, and a late inspection can hold up the draw while the subcontractors still expect payment on time. The builder needs to map the cash in and cash out month by month, not just the total.
The security of payment regime in NSW is designed to make sure contractors are paid for work they have done, and the NSW Government guidance on security of payment explains the basic framework. It does not remove the cash-flow gap, though. A builder can have a valid claim and still be short of money while the claim is being assessed, and a scheme with several claims running at once makes that shortfall easier to hide and harder to fix.
Overheads that do not scale in a straight line
Overheads on a multi-unit scheme are partly fixed and partly variable. The site office, the temporary fencing and the supervisor are fixed for the length of the job. The inspections, the approvals and the insurance rise with each stage and each unit. The problem is that many estimates treat all overheads as if they grow in step with the number of dwellings, and that understates the cost of the early stages, when the fixed items are at their most expensive relative to the work done.
Look at the program as well as the price. A scheme that takes longer than planned carries its fixed overheads for more weeks than the estimate allowed, and the margin falls with every week of delay. A builder who holds the supervisor and the site office for a stalled approval is paying for nothing except the time, and the client is unlikely to accept a variation for that.
Scale also changes the supervision. One supervisor can run a single house with ease. Running several units at different stages needs a supervisor who can plan the sequence, keep the trades coordinated and spot a problem before it reaches the next unit. The cost of that role is real, and it belongs in the estimate from the start.
Concentration of risk across the units
The biggest difference between a single house and a medium-density scheme is the concentration of risk. On one house a failed inspection, a wet winter or a bad subcontractor is a bad job. On a multi-unit site the same event can reach every unit at once, because they share the foundations, the drainage, the services and the program. A defect in the common footing or the shared stormwater line is not a single defect. It is a defect in every dwelling that depends on it.
Warranty and defect exposure follow the same pattern. A builder remains answerable for residential building work under the warranty and consumer rules that apply to it, and a scheme with several dwellings multiplies the number of owners who may come back with a concern. The conversation with one owner about a crack or a leak becomes a conversation with every owner who bought into the same building.
Buyer risk is concentrated too. A scheme that depends on the sale of several units to a small number of buyers, or on one finance provider, can stall if one buyer defaults or one lender withdraws. The article on pipeline risk when one client dominates covers that concentration in more depth, and the same logic applies to a single development that depends on a narrow group of purchasers.
Approvals, staging and the cost of delay
Medium-density work usually runs through a planning and a construction approval process that is more involved than a single house. The BASIX assessment for each dwelling, the conditions of the consent and the requirements for inspections all have to be in place before the work can proceed to the next stage. The NSW Planning Portal explains how BASIX fits into planning approvals, and the scheme’s program should show each approval as a dated stage, not a vague assumption.
A delay in an approval does not stop the cost. It stops the revenue and it extends the overheads, while the subcontractors who were booked for the stage either wait or move on to another job. Build a realistic allowance for approval time into the program, and treat any stage that depends on a third party as a risk to be priced. The cheapest way to avoid a delay is to find the approval gap early, before the crew is on site.
Staging helps here. If the scheme can be divided into stages that do not depend on each other, a delay in one stage need not stop the others. A builder who has planned the stages properly can keep the crew busy on the units that are ready, while the approval for the next group comes through.
Contract structure and who carries the variation risk
The contract decides who carries the risk of a change. A fixed-price contract for a multi-unit scheme puts most of the risk of cost increases on the builder, while a cost-plus arrangement puts more of it on the client. Neither is right or wrong in itself. The question is whether the builder has priced the risk it is accepting, and whether the contract gives a clear route to recover the cost of a change that the builder did not cause.
Variations on a scheme are harder to manage than on a single house. A change to the common services affects every unit, and a change requested by one buyer may have knock-on effects for the others. Put a clear variation procedure into the contracts, and make sure each buyer understands that a change to the shared elements is a change to the whole project.
The NSW Government guidance on contracts for home building work is a useful reference for the terms a written agreement should cover. Check that the contracts for each unit are consistent with each other, because a scheme where every buyer has different terms for the same shared work becomes very difficult to administer.
A worked example: the small townhouse scheme that stalled
Consider a builder in the Hunter who takes on a small townhouse scheme on a site behind an existing street frontage. The estimate is built from the cost of a single house, multiplied across the units, with a modest allowance for the shared driveway and the common drainage. On paper the margin looks healthy. The builder signs the contracts with progress payments tied to stages, and starts work with two crews.
Within the first stage the cash problem appears. The materials for the first units arrive in the same week as the subcontractor invoices, and the progress claim for the first unit is held up by a dispute over a variation the buyer did not expect to pay for. The builder carries the cost of the units through the holding period. The second crew is paid to wait for a wet spell and an inspection that has been moved, and the overheads run on while the stage is held.
The builder recovers only by drawing on a line of credit at a rate that was not in the estimate, and by reorganising the program so one crew moves across the units in sequence. The scheme finishes, but the margin on the early units is largely consumed by the cash cost and the delay. The last unit, which was staged last and paid on settlement, carries most of the profit.
The lesson is that the estimate looked at the cost of the units but not at the timing of the cash, the overheads or the concentration of the risk. A feasibility check that tested the cash flow against a delay would have shown the problem before the contracts were signed.
The cash gap nobody priced. The mistake that costs the most is an estimate that prices the units but not the months between paying for them and being paid. A scheme can be profitable on paper and still fail because the bank balance reaches zero during the build.
A single house and a multi-unit scheme behave differently
| Single house | Multi-unit scheme |
|---|---|
| Cash is tied up in one dwelling | Cash is tied up across several dwellings at once |
| Overheads are carried for one job | Fixed overheads are spread but carried longer if the program slips |
| One delay affects one client | One shared delay can reach every unit |
| Approvals are usually a single process | Approvals and inspections repeat by stage and by unit |
| Margin is mostly price less cost | Margin also depends on staging, cash timing and risk |
Testing the numbers before you commit
A feasibility study for a medium-density scheme should be built around the cash and the program, not just the price. Start with the monthly cash flow, showing every payment out and every receipt in. Then test that cash flow against the things most likely to go wrong: a late approval, a wet period, a subcontractor who cannot start on time, and a buyer whose settlement moves back.
Next, look at the overheads and check that the estimate carries the fixed costs for the length of the program the scheme is likely to take, not the length the developer hopes for. Check the staging, and identify which stages depend on which approvals. Finally, look at the concentration of risk: the shared elements, the buyers, the lender and the crew.
The steps below set out a practical order for that test. It is not a substitute for proper financial advice, which a builder should take from an accountant or a financial adviser who knows the business. It is the builder’s own check on whether the scheme can be built without the business running out of money.
Testing a medium-density scheme before signing
- 1Build the monthly cash flowShow every payment out and every receipt in, month by month, against the staging.
- 2Stress the cash flowTest it against a late approval, a wet period and a settlement that moves back.
- 3Check the overheads against the programCarry the fixed costs for the length the scheme is likely to take, not the best case.
- 4Map the approvals to the stagesShow which stage depends on which approval, and what happens if it arrives late.
- 5Assess the concentration of riskLook at the shared elements, the buyers, the lender and the crew as single points of failure.
The scale of a medium-density project can be a real opportunity for a builder who understands the mechanics. The PointCPD guide to NSW builder CPD sets out how professional development supports that kind of business planning, and the course catalogue includes modules on business planning and contracts that sit alongside this work.
The rule for medium-density work is simple to state and harder to follow. Price the cash, the overheads and the concentration of risk as carefully as the units, and do not sign a scheme whose margin depends on everything going to plan.
Questions builders ask
Is a medium-density project more profitable per unit than a single house?
It can be, because fixed costs are spread across the units and repetition improves productivity. But the margin is also reduced by longer overheads, cash timing and the cost of delay. The honest answer depends on the staging, the program and how the risk is priced. Test the whole scheme, not one unit.
What usually goes wrong first on a townhouse project?
Cash flow is the usual first failure. Materials and labour are paid as the work happens, while progress payments or settlements arrive later and sometimes in lumps. Map the money month by month and stress it against delays before the contracts are signed.
How should overheads be allocated across the units?
Work out the total overhead cost of the whole scheme, including the site establishment, supervision, insurance, finance and approvals, before dividing it among the units. Consider how long the fixed items will be carried, because a slow program raises the overhead on every unit.
Does a bigger scheme increase the defect risk?
The risk is concentrated rather than necessarily higher. A fault in a shared footing, drainage line or service affects every dwelling that depends on it, and each owner may raise a concern. Good inspection and documentation of the shared elements is the best protection.
What should the contracts say about variations on a multi-unit scheme?
Set out a clear variation procedure in each contract, and explain that a change to a shared element affects the whole project. Keep the terms consistent across the buyers wherever the shared work is concerned, so the scheme can be administered without argument.
Should a builder test the feasibility of a scheme with an accountant?
Yes. The builder can do a practical check on the program and the cash flow, but a qualified accountant or financial adviser should review the funding, the tax position and the financial exposure. The builder’s own analysis makes that conversation faster and more useful.
Sources
- Projects · Contour3D
- Continuing professional development for builders and swimming pool builders · NSW Government
- General building work licensing · NSW Government
Published 18 October 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.
