Seven checks before you sign
- Are they a registered builder? A granny flat is a home (Class 1a), so building work worth $20,000 or more that needs a permit must be done by a registered builder. The $50,000 exemption since July 2026 only covers sheds, garages, carports and patios. Check the builder with the state's Find a registered builder search.
- Is there a written contract? For home building contracts between $7,500 and $500,000, the Home Building Contracts Act applies. The contract must be in writing and signed by both of you, and the builder must give you the "Notice for the homeowner" first.
- Is the deposit 6.5% or less? That's the legal maximum before work starts on these contracts.
- Do progress payments match the work? You should only pay for work done or materials delivered. Upfront payments beyond the deposit aren't allowed and can affect your insurance claim.
- Have you seen the home indemnity insurance certificate? It's required for permit work over $20,000. Check it on QBE's online register, and don't pay anything until it's in place. It covers loss of deposit (up to $40,000) and incomplete or defective work (up to $200,000) if the builder dies, disappears or goes broke.
- Who handles the approvals? Ask if the quote includes the plans, energy efficiency report, engineering, building permit and, if needed, planning approval. A granny flat always needs a building permit.
- Will the design pass? Make sure it's no more than 70 m² and meets your council's rules. Some councils, like Joondalup, also want an extra parking bay and matching materials.
Watch out for "plans first" agreements
A preparation of plans agreement (PPA), where you pay a builder to draw plans before the main contract, isn't part of the building contract, so it isn't covered by home indemnity insurance.
After it's built
In WA, builders must fix defective work for six years after practical completion. Complaints go to the Building Commissioner.