A Comprehensive Guide to Granny Flats in Western Australia: Costs, Regulations & Design Ideas
Granny flats are having a moment in WA. A 2024 update to the Residential Design Codes (R-Codes) made compliant ancillary dwellings easier to deliver, which matters when families want flexible space and owners want more value from their land.
Since early 2024, an R-Code-compliant granny flat can be built on a residential lot of any size without planning approval, provided it meets local setbacks and stays within the size cap.
What qualifies as a granny flat in WA?
In planning terms it’s an “ancillary dwelling”: a self-contained home on the same lot as an existing house. It can be attached or detached, and it may be rented to people who aren’t related to the main household. You can’t sell it off separately unless subdivision or survey-strata approval is obtained.
Key rules to know (2025)
- Maximum internal floor area: 70 m² under R-Codes Volume 1. Some local governments apply an accessibility concession up to 80 m² when certain design features (e.g. wider doors and corridors) are included. Always check the current clause and your council’s practice.
- Planning approval: Generally not required if the dwelling meets the deemed-to-comply standards. The 2024 amendments removed the previous minimum lot size and opened up more strata scenarios.
- Parking: In most cases, no extra bay is required for a compliant ancillary dwelling under the revised R-Codes, except in certain densities or locations where car dependence is likely.
- Building permit: Always required. Councils apply statutory fees set by WA legislation (see “Approvals & fees” below). Some titles with common property are excluded; for example, the City of Melville specifies no common property on the land title.
Approvals & fees (what to budget beyond the build)
Even when planning approval isn’t needed, you still lodge a building permit application. Typical statutory charges include:
- Application fee – a set percentage of the project value, with a minimum fee applying.
- Building Services Levy – calculated as a small percentage of the overall works, or a fixed amount for lower-value projects.
- Construction Training Fund (CTF) levy – applies once the project value passes a certain threshold and is payable before building begins.
Local councils may also add their own charges, such as bonds or verge protection fees, so it’s important to confirm the full schedule of costs when lodging your application.
Design ideas that work in WA conditions
Plan for orientation and summer shade – the move to NCC 2022 energy efficiency in WA in 2025 lifts performance expectations to a 7-star minimum. Good orientation, cross-ventilation, effective shading and higher-performing glazing will help you meet the rating without over-engineering.
Think like a small home, not a big room – separate the living edge from bedroom walls for better acoustic comfort; tuck services along one wet wall to control costs; and build in storage so the space stays tidy. These choices support both ageing-in-place and rental use.
Accessibility pays back – zero-step entries, 820 mm doors and wider corridors improve everyday use and may qualify for the R-Codes accessibility concession up to 80 m² where applied by your council.
Privacy and outlook – place windows to avoid overlooking the main house and neighbours while capturing light. Courtyards and screens can deliver both privacy and breeze.
Bushfire readiness – if your lot is shown on the Map of Bush Fire Prone Areas, a BAL assessment will set construction requirements (e.g., ember protection, glazing specs). Check the Department of Fire and Emergency Services map and local guidance early.
Servicing and title – confirm sewer connection points, stormwater paths and any strata limitations before committing to a plan. Some titles with common property won’t permit ancillary dwellings.
A practical pathway
- Site check: Confirm zoning, setbacks and whether planning approval is exempt in your case under the current R-Codes. The WA Government’s R-Codes collection page links to the operative documents and practice notes.
- Budget properly: Add permit fees, levies and likely service upgrades to builder quotes so you’re comparing true totals.
- Engage your team: A designer experienced and structural engineer in small-footprint homes can resolve storage, privacy and compliance without bloat.
- Document once, build once: Certified applications typically move faster. Clear drawings, energy reports and a tidy specification give certifiers and builders fewer reasons to pause.
Mandurah and the Peel region add a few site-specific considerations: saline air, coastal winds and, on canal lots, interface sensitivities. If you’re near the waterways, look for professionals who understand canal house design and how services and privacy play out in those settings.
For homeowners wanting a one-stop approach to architectural design and approvals, engaging a local practice can streamline the whole exercise. That’s where a new home designer Mandurah with granny-flat experience earns their keep.
Bottom line
WA has made compliant granny flats simpler to approve, with clear size caps and a straightforward building-permit pathway.
Get the rules right, invest in climate-smart detailing, and you can add a flexible, durable dwelling that stands up to local conditions—and the latest Code.
