How to Estimate a New Home Build
Estimating a new home build means measuring and pricing the complete scope of a house from site works through to handover — every trade, not just one — then assembling those quantities into a single Bill of Quantities and a priced tender or contract sum. Because a new build is usually sold as one fixed price across dozens of trades and stages, missing scope in any single trade erodes the margin on the whole job, which is why a complete, structured takeoff matters more here than on a smaller, single-trade job.
Key takeaways
- A new home build estimate has to cover every trade across the whole job — site works and slab, frame, lock-up, fit-out and completion — assembled into one Bill of Quantities, not priced trade by trade in isolation.
- Preliminaries — site establishment, supervision, insurances and holding costs — sit alongside the trade costs and are one of the easiest things to under-price on a fixed-price new build.
- Provisional sums and PC items let you put a genuine fixed price on a new build before the client has finalised every selection, without under-quoting the job.
- Progress claims on a new build are usually billed against the same construction stages the estimate was built around, so a well-structured Bill of Quantities pays off again once the job is under way.
- Automated takeoff from a full plan set is 60-75% faster than measuring a new home build by hand — which matters most on exactly this kind of trade-heavy, high-scope job.
What makes estimating a new home build different
Estimating a new home build is different from estimating a single trade or a small job because you are pricing an entire house, across every trade, as one fixed-price contract sum rather than a series of separate quotes.
A bathroom reno might involve three or four trades and a takeoff you can hold in your head. A new build runs to dozens of trades — site works, concrete, framing, roofing, cladding, plumbing, electrical, insulation, plasterboard, cabinetry, painting, flooring and tiling — each with its own quantities and rates. Because the build is priced as one number, an error in any single trade comes straight off the margin on the whole job.
Building a Bill of Quantities across every trade
A Bill of Quantities for a new home build is a single structured document listing every measured item of work across every trade, with its unit, quantity and rate, so the whole house is priced from one consistent set of quantities rather than a stack of separate trade quotes.
Rather than waiting on quotes from every subcontractor before you can price the job, a BOQ lets you measure the full plan set yourself — or have it measured automatically — and apply your own rates library across every trade, so you control the number from the outset.
- Substructure — site preparation, excavation, footings and slab or subfloor.
- Structure — timber or steel framing, roof trusses and structural steel.
- External envelope — roofing, cladding or brickwork, windows and external doors.
- Services — plumbing, electrical, hydraulics and mechanical, roughed in and fitted off.
- Internal fit-out — insulation, plasterboard, cabinetry, tiling, flooring and painting.
- Preliminaries and external works — site costs, driveways, fencing and landscaping.
The construction stages a new build estimate follows
Most new home build estimates and contracts are structured around the same handful of construction stages, because those stages match how the job is actually sequenced on site and how progress claims are usually billed.
Working stage by stage also makes an estimate easier to check for missing scope, since each stage has a well-understood, predictable set of trades that should appear in it.
- Site preparation and slab — demolition, excavation, footings, drainage and the concrete slab or subfloor.
- Frame — timber or steel wall framing, roof trusses and structural steel.
- Lock-up — roofing, external cladding or brickwork, windows and doors, so the building is weatherproof.
- Fit-out — internal linings, cabinetry, tiling, flooring, painting, and fit-off of plumbing and electrical.
- Completion — fixtures, final trades, cleaning and the handover inspection.
| Stage | Typical scope | Illustrative share of contract sum |
|---|---|---|
| 1. Site prep & slab | Demolition, excavation, footings, concrete slab | 10-15% |
| 2. Frame | Wall framing, roof trusses, structural steel | 10-12% |
| 3. Lock-up | Roofing, cladding or brickwork, windows, external doors | 20-25% |
| 4. Fit-out | Linings, cabinetry, tiling, flooring, painting, fit-off | 30-35% |
| 5. Completion | Fixtures, final trades, clean, handover | 8-12% |
| Preliminaries | Site establishment, supervision, insurances (spread across stages) | 8-12% |
Preliminaries: the site costs that sit outside the trades
Preliminaries are the costs of running the job itself rather than building any single part of the house — site supervision, site establishment, temporary fencing and toilets, insurances, and the cost of holding the site for the length of the build — and they need to be priced explicitly, not absorbed as an afterthought.
Because preliminaries are spread across the whole program rather than tied to one trade, they are easy to under-estimate: a longer program caused by weather or a slow trade quietly increases supervision and holding costs even though no single trade line item has changed.
What usually counts as a preliminary
Site supervision and project management, site establishment (sheds, temporary power and water, signage), safety and insurances, temporary fencing and toilets, and the cost of holding the site for the length of the build.
Provisional sums and PC items for undecided selections
Provisional sums and PC (prime cost) items let you put a fixed price on a new home build before the client has finalised every selection, by allocating a stated allowance for an item that is not yet locked in, rather than guessing a number or delaying the whole quote.
A provisional sum is used where the scope itself is not yet fully known — for example, site works where soil conditions are uncertain until excavation starts. A PC item is used where the scope is known but the product has not been chosen — for example, tiles, tapware or a kitchen, priced at a stated allowance until the client selects the actual item.
- Typical PC items — tiles, tapware and sanitaryware, kitchen and joinery, floor coverings, light fittings and appliances.
- Typical provisional sums — site works with unknown ground conditions, service connections, and scope depending on an authority approval not yet finalised.
- Every provisional sum and PC item should sit on its own line in the Bill of Quantities, with the allowance clearly stated.
Structuring progress claims against the estimate
Progress claims on a new home build are usually billed against the same construction stages the estimate was built around — site prep and slab, frame, lock-up, fit-out and completion — so a well-structured Bill of Quantities pays off again once the job is under way.
Because each stage claim is checked against the value of work actually measured as complete, a BOQ broken down by stage and trade makes a claim easy to justify and hard to dispute — a single lump-sum price with no stage breakdown gives you nothing to point to when a claim is questioned. The same quantities and rates can also be reused to price variations as they arise.
The risk of missing scope on a large fixed-price job
The single biggest risk on a new home build is missing scope somewhere in a plan set that can run to dozens of pages across architectural, structural, hydraulic and electrical drawings — on a fixed-price contract, anything missed at estimating time becomes a cost the builder absorbs, not a surprise the client pays for.
Unlike a single-trade quote, a new build has no natural point where a missed item is likely to be caught before the price is locked in — the whole job is priced and contracted as one number, often months before construction starts, so an error sits quietly in the estimate until the under-scoped trade turns up on site.
- Missing an item on a busy sheet — scope shown on one drawing but not cross-checked against the others.
- Under-estimating preliminaries when the build program stretches out.
- Pricing from an early or superseded plan revision instead of the current issue.
- Setting provisional sums and PC allowances unrealistically low just to keep the price competitive.
- Manually re-keying quantities between a spreadsheet and the tender document.
How My Trade Hub helps estimate a new home build
My Trade Hub reads your full plan set — architectural, structural and services drawings — and performs the automated takeoff across every trade in the build, from site works and slab through to fit-out and completion, instead of you measuring each trade by hand.
Every measured quantity is priced against your own editable rates library, and the output is assembled into a structured Bill of Quantities and tender document — organised by trade and construction stage — so provisional sums and PC items sit alongside firm quantities in the one document, ready to send to a client or head contractor.
Because the takeoff is automated rather than manual, preparing a priced new home build tender is 60-75% faster than doing it by hand — which matters most on exactly this kind of job, where the sheer number of trades and drawing sheets is what makes manual estimating slow in the first place.
Frequently asked questions
how do you estimate a new home build?
You estimate a new home build by measuring the scope from the plans across every trade — site works, frame, lock-up, fit-out and completion — pricing each item against your rates, adding preliminaries and provisional sums for undecided scope, and assembling the result into one Bill of Quantities. Automated takeoff makes this 60-75% faster than measuring every trade by hand.
what is included in a new home build estimate?
A new home build estimate should include every trade needed to complete the house — site preparation and slab, frame, roofing and external envelope, all services, internal fit-out and completion trades — plus preliminaries for site running costs, provisional sums for undecided scope, and PC items for products the client hasn’t yet selected.
what is the difference between a provisional sum and a pc item?
A provisional sum applies where the scope itself is not yet fully known, such as site works before ground conditions are confirmed. A PC item applies where the scope is known but the product hasn’t been chosen, such as tiles or tapware — the contract carries an allowance until the client selects the item and the price is adjusted to the real cost.
how are preliminaries calculated on a new build?
Preliminaries are calculated by itemising the actual costs of running the job for its full program — site supervision, site establishment, insurances, temporary fencing and toilets, and holding costs — rather than applying a rough percentage at the end. These costs need to be estimated against the expected duration of the build, not against any single trade.
how do progress claims work on a new home build?
Progress claims on a new home build are usually billed stage by stage — site prep and slab, frame, lock-up, fit-out and completion — against the value of work measured as actually complete at each stage. A Bill of Quantities structured by stage and trade makes each claim straightforward to justify against the original estimate.
what causes builders to lose money on fixed-price new builds?
Builders most commonly lose money on fixed-price new builds by missing scope somewhere in a large plan set, under-estimating preliminaries when the program runs long, setting provisional sums or PC allowances too low to keep the price competitive, or introducing errors while manually re-keying quantities into the final tender document.
how long does it take to estimate a new home build?
Measuring and pricing a new home build by hand can take an experienced estimator several days, given the number of trades and drawing sheets involved. Automating the takeoff cuts that time by 60-75%, turning the same job into a priced Bill of Quantities in a fraction of the time.
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