WA granny flat rules,
the 70m2 rentable limit.

An ancillary dwelling is a self contained second home on the same lot as a main dwelling, with its own kitchen, bathroom and living area. It is the formal R-Codes term for what most people call a granny flat in Perth.

The R-Codes define an ancillary dwelling as self contained accommodation on the same lot as a single house, sharing the same title. It is different from a second separate dwelling, a grouped dwelling, or a dual-key home where two tenancies sit under one roofline. The ancillary dwelling has its own entry, its own services and its own private outdoor space, but it cannot be sold or strata-titled separately from the main home. That single-title structure is what keeps the approval path simple and the cost down.

The deemed-to-comply floor area for a WA ancillary dwelling is 70m2, measured to the outside of the external walls and excluding open verandahs and carports. It rises to 80m2 where the dwelling is designed for accessibility under the R-Codes.

Staying within 70m2 is what keeps the whole footprint rentable and the approval deemed-to-comply. Of our 8 granny flat designs, 4 sit within the 70m2 limit, so the entire dwelling is rentable as an ancillary. The larger designs over 70m2 are still valuable, but they typically suit a second separate dwelling, a dual-occupancy arrangement, or an accessible build, rather than the standard ancillary pathway. We confirm which path your block and design fall under before you commit.

• Open verandahs and carports are generally excluded from the 70m2 calculation, so a covered alfresco does not eat into your living area.
• Accessibility designs can use the 80m2 allowance, useful for ageing-in-place or adaptable layouts.
• Floor area is to the external wall face, so plan early. Small layout changes can push a design over the cap.

Before 2020 a WA ancillary dwelling could only house a family member. Since 2020 it can be rented to anyone on the open market, with no special permission required to list it. That change is what turned the granny flat into a genuine dual income asset.

The rent-to-anyone reform is the single most important rule for investors. Combined with the removal of the 350m2 minimum lot size and the extension to grouped, multiple-dwelling and strata lots, far more Perth blocks can now carry a rentable second income than even a few years ago. It means an owner-occupier can let the granny flat to offset a mortgage, and an investor can run two leases on one title. See how the numbers work on the rental yield page and the granny flat investment case.

If your ancillary dwelling meets every deemed-to-comply requirement, including the 70m2 cap, setbacks, open space and parking for your suburb, planning approval is generally not required. A building permit is always required before construction starts.

1. Check deemed-to-comply. Confirm floor area, setbacks, open space and parking against the R-Codes and your local planning scheme.
2. Planning approval if needed. If any element falls outside deemed-to-comply, a development application to your council is required.
3. Building permit. Always required. Lodged with your local government or a private certifier with the construction documents.
4. Build. Allow around 8 months from contract to handover through our panel, after design, approvals and siteworks.

Because setbacks, open space and crossover rules differ council to council, the deemed-to-comply detail is the part to verify early. The Property Plug confirms it for your specific lot and local government area before you sign, so there are no approval surprises later.

• Granny flat hubAll 8 designs, a yield worked example and the price list.
• Granny flat cost in PerthBuild bands, siteworks and what all-in includes.
• Granny flat investmentDepreciation and the dual income thesis.