"Unexpected structural issues" on a final invoice, with no paperwork you ever signed. In NSW, a variation that wasn't documented in writing may not be legally valid — no matter how convincingly it's explained after the fact.
The legal requirement, stated plainly
Under section 7E of the Home Building Act 1989 (NSW), variations to residential building contracts must be in writing. In practice, many builders still rely on verbal agreements, text messages, or informal emails that don't meet this legal threshold — which matters enormously if a dispute over cost or scope arises later.
What standard contracts actually require
Standard industry contracts (such as those published by the HIA) build this requirement directly into their variation clauses: variations require written, signed orders before the changed work begins, specifically to prevent scope creep and protect both parties. Under a typical HIA contract, a builder generally has the right to refuse a variation request without giving a reason — but the reverse also holds: a builder generally cannot unilaterally charge you for a variation you never approved in writing.
The narrow exception worth knowing about
There's one significant carve-out: homeowners must not unreasonably withhold consent to a variation that's genuinely required for the work to comply with the law or a requirement of a council, certifier, or other statutory authority. If a building inspector mandates a change to meet code, that's treated differently from a builder unilaterally deciding to upgrade materials or change the scope for their own reasons.
Common places surprise variations hide
- Provisional sums and prime cost items: allowances in the contract for items not yet finalised — these often generate legitimate variations when actual costs differ, but the builder should still be substantiating the difference with supplier invoices and quotes, not just an inflated final figure
- "Unexpected" structural issues: genuine surprises do happen in renovation, but a real one should come with photographic evidence and a written variation proposal before the extra work proceeds, not just an explanation on the final bill
- Material substitutions: a genuine supply shortage might justify a substitution, but deliberate downgrades still require your written approval, not just a builder's unilateral decision
How to challenge an unapproved variation charge
- Check whether you ever signed or otherwise approved the specific variation in writing — a text message agreeing to a general idea isn't the same as approving a priced, scoped variation order.
- Request the underlying documentation — supplier invoices, quotes, or photos — substantiating any claimed cost increase.
- State clearly, in writing, that you dispute any charge for work that wasn't approved as a written variation under section 7E.
- Note that payment for a properly approved variation is typically due at the next progress payment stage, not necessarily all at once at project completion — check what your specific contract says.
- If the dispute isn't resolved directly, this becomes grounds for a formal complaint to NSW Fair Trading or the equivalent body in your state.
What this means practically
- A variation charge with no written, signed documentation may not be legally enforceable in NSW under section 7E of the Home Building Act.
- Genuine unexpected issues should still generate a written variation proposal before extra work proceeds — not just an explanation after the invoice arrives.
- Homeowners can generally refuse variations that aren't legally required, but cannot unreasonably refuse ones mandated by a council or certifier for code compliance.
- Keep a running log of every variation request and your response — this becomes essential evidence if a final-bill dispute arises.
Sources
- Contracts Administrator — HIA Contract Variation Documentation and Home Building Act s 7E requirements: contractsadministrator.com.au
- Contracts Specialist — Effective Management of Variations, HIA NSW Residential Building Contract: contractsspecialist.com.au
Related Kibbo Tools
- Home Renovation Contract Checklist — confirm your contract's variation clause requires written approval before you sign.
- Contractor Dispute & Demand Letter Generator — challenge an unauthorized overcharge formally in writing.