Builder Specification Traps: What to Check Before You Sign a Building Contract in WA

The most expensive words in residential construction are 'I assumed that was included.' Builder contracts in WA can look identical at headline price while concealing tens of thousands in specification gaps. Here's where those gaps hide.

This is not legal advice, for contract review you should engage a lawyer. What this is is a practical guide to the specification and documentation gaps that cause the most pain for Southwest residential clients, drawn from real project experience.

The specification is not a formality

A building quote is only meaningful in relation to its specification. Two contracts quoting the same house at similar prices can represent significantly different products. The difference is in the detail, or the absence of it.

Price comparison without specification comparison is not comparison at all. It's a gamble.

1. Provisional sums and prime cost items

A provisional sum (PS) is an estimate included in the contract for work where the scope or cost cannot be fixed at the time of signing. A prime cost (PC) item is an allowance for a product you will select later, appliances, tapware, light fittings.

Both are legitimate contract mechanisms, but both transfer cost risk to you. If the PS for site works is $10,000 and the actual bill is $28,000, you pay the difference. If the PC for kitchen appliances is $1,800 and you choose a realistic mid-range product, you pay the gap.

Practical check: List every PS and PC item in any contract you're comparing. Ask the builder to justify each sum with a preliminary assessment. Low PS and PC figures are the most common mechanism for reducing a headline quote while protecting builder margin through post-contract variations.

2. Site costs listed as 'to be confirmed'

Site costs cover earthworks, cut and fill, retaining walls, slab upgrades for reactive soil, and service connections. On a flat block in a serviced estate, site costs can be modest, $5,000–$10,000. On a sloped block, a Class H reactive soil site, or a rural block without nearby services, they can add $25,000–$60,000 to the project cost.

A contract that lists site costs as 'TBC' or includes a $5,000 allowance without a supporting soil test or site inspection is not a fixed-price contract, it's a variable-price contract with the variable undisclosed.

Push for a preliminary soil test (typically $800–$1100) and a site cost estimate from your builder before you sign. That's a very small investment to lock in a realistic figure.

3. Standard range versus what you want

Most builder contracts specify finishes by reference to the builder's 'standard range.' Until you've physically seen the standard range and had its inclusion confirmed in writing, you don't know what your contract delivers.

Common upgrade cost triggers that catch buyers by surprise:

•      Roof cladding — standard range terracotta or concrete tiles versus Colorbond — often a $3,000–$6,000 upgrade.

•      Bench tops — standard laminate versus stone or engineered stone — $2,500–$8,000 depending on kitchen size.

•      Window frames — standard aluminium versus thermally broken or uPVC — $4,000–$12,000 on a full home.

•      Ceiling height — 2400mm standard versus 2700mm — cost impact is $5,000–$12,000.

•      Floor tiles — standard 300×300 versus large-format — $3,000–$8,000 in material and labour uplift.

4. What is excluded altogether

Exclusions that are not mentioned in conversation but are listed in the contract fine print, or not listed at all because they're simply assumed to be the owner's cost:

•      Landscaping and driveways — almost always excluded; budget $15,000–$40,000 separately depending on scope.

•      Fencing — excluded in most contracts; often required as a council occupancy condition.

•      Clothesline and letterbox — minor but sometimes required for certificate of occupancy.

•      Development application fees — check who pays, DA fees in South West WA councils range from $500–$3,500 depending on project value.

•      Headworks contributions — Water Corporation and sometimes local councils charge infrastructure contributions on new dwellings or additions. For a new Southwest residential lot, Water Corporation headworks can range from $10,000–$20,000+ depending on connection requirements.

5. Variation clauses and authority

WA's Home Building Contracts Act 1991 requires all residential contracts over $7,500 to be in writing. It also regulates how variations must be authorised. But what it requires is a floor, not a ceiling, many builder contracts have variation clauses that are broader than the Act's minimum protections.

Check: who can authorise a variation, at what rate labour variations are charged, and whether there is a process for disputing a variation amount before it's authorised. 'Authorised in writing' should mean you, not just someone on site.

6. Construction timeline - extensions of time

The Home Building Contracts Act requires a contract to include a start date and completion period. Extension of time (EOT) clauses are standard, but what qualifies as a valid EOT varies significantly between contracts. Rain delays, subcontractor availability, and material supply issues may all be listed as valid EOT grounds.

For investment properties or builds where timing has financial implications, understand how EOT is triggered, how it is notified, and what liquidated damages (if any) apply if the builder fails to complete.

Frequently Asked Questions

Is a fixed-price contract actually fixed in WA?

A fixed-price contract fixes the price for the documented scope but variations can still arise from client-initiated changes, genuinely unforeseen site conditions, and where provisional sums or prime cost items are included. The more thoroughly the scope is documented before signing, the more genuinely 'fixed' the price is in practice.

Do I need a lawyer to review a building contract in WA?

It's not legally required, but it is recommended for contracts above $250,000. A building lawyer can identify non-standard clauses and advise on risk. A building consultant (like a building designer with project management experience) can review the specification and scope for gaps, a different but complementary review.

What is a headworks contribution?

Headworks contributions are infrastructure charges levied by Water Corporation (and sometimes local councils) to connect a new or additional dwelling to water and sewer infrastructure. They are based on the demand a new dwelling places on the network. For a new Southwest residential project, allow $10,000–$20,000+ as an indicative budget item, confirm the actual figure with Water Corporation for your specific lot before signing a contract.

We offer pre-contract specification reviews as part of our project management service. It's one of the most cost-effective checks you can make before a build — projects@fastlanedesign.com.au