Granny Flats & ADUs in Perth metro
Guide to Perth granny flat and ADU builders: what the work involves, what separates a solid contractor from a risky one, and how our scoring works.
A granny flat, or ancillary dwelling unit (ADU), is a self-contained secondary home built on a block that already has a main house. In Perth metro that usually means a one or two bedroom unit with its own kitchen, bathroom and entry, either as a standalone build in the backyard or a conversion of an existing structure like a garage or workshop. People build them to house a parent or adult child, add a rental income stream, or increase the resale value of a property that has spare land. We've listed 20 businesses in this category that handle this kind of work across the metro area.
The job involves more than carpentry. A builder needs to manage council approvals, deal with the specific R-Codes and setback rules that apply to secondary dwellings in WA, coordinate site works, plumbing, electrical and often a separate driveway or meter, and hand over something that meets the same building code as a full house. When you're comparing contractors, look for a firm that can show you completed granny flat projects (not just main house renovations), give you a fixed-price contract rather than a vague estimate, and explain upfront how they handle council approval timelines and any retaining or drainage issues on sloped blocks, which are common in the hills suburbs.
Our scoring weighs verified reviews, how consistently a business responds to jobs in this category specifically, and signals of licensing and follow-through on approvals. For the full ranked list, see our best renovation contractors guide, and for a breakdown of how we calculate scores, check our methodology page.
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All granny flats & adus, ranked by score and relevance
20 businesses. The order weighs each business's overall score by how much of its reviewed work is granny flats & adus, so a lower-scored specialist can rank above a higher-scored generalist. Filter and sort below, or open the full map view.
When you submit a form on this site, your enquiry may be shared with partner providers able to do the work. We may receive a referral fee, but our rankings and scores are based on our published method only and are not affected by these fees.
Common questions about granny flats & adus
- How much does a granny flat cost in Perth?
- Most standalone granny flats in Perth range from around $90,000 to $180,000 depending on size, finish level and site conditions, with smaller studio-style units at the lower end and two-bedroom units with higher-spec kitchens and bathrooms pushing toward the top. Sloped or constrained blocks, retaining walls, and connecting new services (power, water, sewer) can add significantly to the base build cost, so a firm quote after a site visit matters more than any published rate.
- Do I need council approval to build a granny flat in Perth?
- Yes. Ancillary dwellings in WA are governed by the R-Codes and local council planning schemes, covering minimum block size, setbacks from boundaries, and maximum floor area. Some smaller, compliant designs can go through as a building permit without a separate planning approval, but many blocks need both. A good contractor will check this against your specific block before you sign anything, not after.
- How long does a granny flat build take from approval to move-in?
- Once permits are through, a straightforward standalone build typically takes 10 to 16 weeks on site. The approval stage itself can add another 6 to 12 weeks depending on the council and whether planning approval is required in addition to the building permit, so total project timelines of 4 to 7 months from first contract to handover are common.
- What should I check to judge if a granny flat builder is any good?
- Ask to see photos or addresses of at least two or three completed granny flats, not just house renovations, since the compliance and services side of a secondary dwelling is different. Confirm they're a registered builder in WA, get the fixed price in writing with an itemised list of inclusions (fencing, driveway, air conditioning, floor coverings are common exclusions that catch people out), and ask directly how they've handled council delays on past jobs.
Guides to choosing granny flats & adus
- Granny flat rules in WA: R-Codes and what's allowed on your block
What WA's R-Codes and council planning rules generally control for a granny flat or ancillary dwelling, and what to check before you commit to a design.