What’s actually included in a fixed-price custom home build?

A genuine fixed-price custom home build includes everything from the soil test to the letterbox in a single contracted amount. That covers site costs, engineering, council fees, BASIX, the build itself, all selections, services connections, landscaping, and driveway. The only items that can reasonably be left as provisional sums are selections the buyer has not made yet (tiles, taps, light fittings). Anything else listed as “provisional” should be questioned.

In NSW, the law allows builders to use provisional sums, but it also requires them to be estimated with “reasonable care and skill” using the information available at the time of the contract. That clause is the difference between a fixed-price tender that holds and a fixed-price tender that does not.

This guide explains what should be in your tender, what should not, and how to read a custom home contract before you sign anything.

What does “fixed-price” actually mean in NSW?

In an NSW residential building, a fixed-price contract (also called a lump sum contract) states the total price up front. The price is fixed for the work specified in the contract, subject to two things:

• Agreed variations. Any change to the contracted scope, in writing, with a documented cost and time impact.
• Reconciled provisional sums. Where an allowance was made for an unselected item, the actual cost is reconciled against the allowance once the item is selected.

Fixed-price contracts in NSW are governed by the Home Building Act 1989, and the standard NSW Fair Trading home building contract for work over $20,000 is the most consumer-protective option. Industry-issued contracts from the HIA or Master Builders also exist and are commonly used. The contract type matters; the inclusions matter more.

The alternative to a fixed-price contract is a cost-plus contract, where you pay the actual cost of the work plus the builder’s margin, with no upper limit unless one is negotiated. Cost-plus is rarely the right contract for a new home build.

What should be included in a fixed-price custom home tender?

The breakdown below is what a genuine fixed-price tender for a custom home build should cover. Organised by stage.

Stage 1: Pre-construction

• Site assessment. Detailed walk-over, slope measurement, services check, and access review.
• Soil tests and engineering report. Geotechnical assessment to determine slab type and foundation requirements.
• Survey. Contour, boundary, and feature survey of the block.
• Architectural drawings. Plans, elevations, sections, details. Council-ready and construction-ready.
• Structural engineering. Slab, frame, footings, retaining walls (if needed).
• BASIX certificate and NatHERS thermal modelling. Mandatory under the NSW sustainability requirements for new homes.
• Development Application or Complying Development Certificate. Lodgement, documentation, and any council follow-ups.
• Council fees. Including section 7.11 contributions (developer contributions) where applicable.
• Construction certificate. The approval that allows work to start on the site.

Stage 2: Site works

• Demolition. If this is a knockdown rebuild, end-to-end demolition coordination should be in the tender, not contracted separately by you.
• Service disconnection. Electricity, water, gas, telecommunications, sewer to council requirements.
• Site cut and fill. Excavation to the agreed level.
• Piers, retaining walls, and stormwater drainage. Where the site requires them.
• Site preparation and protection. Fencing, sediment control, and tree protection.

Stage 3: Slab and frame

• Slab. Concrete, reinforcement, in-slab plumbing and electrical conduit, and termite protection.
• Frame. Timber or steel frame, roof trusses, internal walls.
• External wall cladding. Brick, render, weatherboard, or specified equivalent.
• Roofing. Tile, Colorbond, or specified equivalent. Gutters, downpipes, flashings.

Stage 4: Lock-up

• Windows and external doors. Including any glazing upgrades (e.g. BAL-rated, acoustic, or thermal performance glazing required by BASIX).
• External waterproofing. Decks, balconies, wet areas.

Stage 5: Fit-out

• Internal linings. Plasterboard, ceiling, cornices, skirtings.
• Electrical fit-off. Switches, GPOs, light fittings (per the selection schedule).
• Plumbing fit-off. Taps, mixers, toilets, basins, baths, showers.
• Kitchen. Cabinetry, benchtops, splashback, and appliances per schedule.
• Bathrooms. Cabinetry, tiling, fixtures, screens, and accessories.
• Wardrobes, linen, mudroom and storage joinery.
• Internal doors and hardware.
• Flooring. Tile, timber, carpet per schedule.
• Painting. Interior and exterior to specification.

Stage 6: Practical completion

• Driveway. Concrete, paver, or exposed aggregate to specification.
• Landscaping. Turf, garden beds, mulch, and any specified plantings.
• Fencing. Side and rear boundary to standard specification.
• Letterbox and clothesline.
• Final clean.
• Compliance certificates. Plumbing, electrical, occupation certificate from the certifier.

Stage 7: Post-handover

• Defects liability period. Typically 13 weeks (90 days) for boutique builders, longer under some industry contracts.
• Statutory warranty. Six years for major defects, two years for minor defects, under the NSW Home Building Act.

What is reasonable to leave as a provisional sum, and what is not?

A provisional sum is an estimated dollar amount for an item that genuinely cannot be priced at the tender stage. The reconciliation mechanic is set out in the NSW Fair Trading home building contract: if the actual cost is higher than the allowance, the buyer pays the difference plus the builder’s margin. If lower, the contract price reduces.

Reasonable to leave provisional

• Tiles, taps, light fittings, and other finish selections that the buyer has not chosen yet. These genuinely cannot be priced until selected, and a clear allowance lets the buyer browse without holding up the tender.
• Kitchen splashbacks and feature elements are where the buyer wants time to decide.
• Some appliance selections where models change frequently.

Not reasonable to leave provisional

• Site costs. Excavation, retaining, piers. A thorough site assessment can price these before the contract.
• Council fees and section 7.11 contributions. These are published by the Central Coast Council and can be calculated up front using the DA fee estimate calculator.
• BASIX and NatHERS certification. Fixed cost.
• Demolition (in a knockdown rebuild). Quotable from the demolisher before the contract.
• BAL or flood compliance work. If the block has a BAL rating or flood overlay, the design response can be priced.
• Engineering and structural design. Quoted by the structural engineer before the contract.

If your tender lists any of the second category as a provisional sum, ask why. The answer “we can’t price that yet” is often a code for “we didn’t do the work to price it.” It is not a code for “this genuinely cannot be priced.”

How to read a custom home tender line by line

A well-structured fixed-price tender has six parts. Look for all of them.

1. The lump sum price, clearly stated and inclusive of GST.
2. The schedule of inclusions: what is being supplied, by whom, and to what specification. Look for brand names and model numbers, not “quality fixtures throughout”.
3. The selection schedule: what the buyer has chosen so far, by name. Tiles, taps, lighting, paint, cabinetry, benchtops, flooring. Anything not yet selected should appear here with a provisional allowance.
4. The provisional sum schedule: every PS, the amount, and a brief description. Two or three is normal. Twenty is not.
5. The variations process: how variations are quoted, approved in writing, and added to the contract price.
6. The deposit and progress payment schedule: under NSW law, the initial deposit on contracts over $20,000 is capped at 10% of the contract price.

The schedule of inclusions and the provisional sum schedule are the two most important documents in any custom home contract. Read them together. What is missing from the schedule of inclusions usually shows up as a provisional sum, or worse, as a “variation required after contract”.

Red flags in fixed-price custom home tenders

Five things to watch for.

• Vague scope language. “Kitchen as discussed” is not enough. The schedule should state the cabinetry brand, benchtop material, splashback, appliance models, and finishes.
• A long provisional sum list. Three to five PS for unselected finishes is fine. Fifteen to twenty PS, including site costs and engineering, is a sign the tender was not properly priced.
• “Engineering TBA” or “Site costs to be confirmed”. Both of these can be priced before the contract. If they are not, the contract price is not really fixed.
• A deposit over 10% of the contract value. NSW law caps the deposit at 10% of the contract price for contracts over $20,000. Anything higher should be challenged.
• No selection schedule. If you have made selections and they are not in writing in the contract, they have not been agreed.

Why Sanctuary’s tender model is built this way

Sanctuary New Homes was founded on the model that the tender is the contract. Site costs, council fees, BASIX, and landscaping are priced before contract, not after. The mechanism is straightforward: the site assessment is done thoroughly before any tender is issued, which means the cost variables for a complex site (slope, BAL, flood, battleaxe access) are known by the time the price is quoted, not estimated.

Twenty-five years of building on complex Central Coast and Lake Macquarie blocks has produced a body of cost data that lets these variables be priced with confidence, not guessed at. The result is what Sanctuary clients describe in their own words in the testimonials archive: “everything included in the price up front so you know exactly how much to budget for.”

The 90-day maintenance period after handover is part of the contract by default. Any defects raised in writing during the period are attended to without further cost.

Common questions about fixed-price custom home builds

Can the price increase after I sign? Only through agreed variations (which you sign for) or reconciled provisional sums (where you have made a selection that costs more than the allowance). If neither has happened, the price should not change.

What is a prime cost item? A prime cost (PC) item is a specific named product with an allowance attached. It works similarly to a provisional sum but applies to a single named item (e.g. “PC: oven, $2,800”). If you choose an oven that costs more, you pay the difference plus the builder’s margin.

What if I change my mind about selections? Selection changes after the contract become variations. They should be quoted in writing, agreed upon, and added to the contract before the work is ordered. Late changes after the item is on site or installed can be far more expensive.

Does the post-handover maintenance period add to the price? No. The defects liability period is part of the contracted price. Statutory warranties under the NSW Home Building Act apply regardless.

What this means if you are about to sign a tender

A fixed-price tender that has site costs, council fees, BASIX, and demolition (if applicable) priced and included is doing the work the law expects. A tender that lists those items as provisional is not.

Before you sign anything, read the schedule of inclusions and the provisional sum schedule side by side. Read the NSW Fair Trading Consumer Building Guide. Ask your builder to explain any provisional sum in plain English, and ask why it could not be priced before tender.

If you want a tender that prices everything before contract on a Central Coast or Lake Macquarie block (including complex sites), get in touch for a no-obligation site assessment.