Perth homeowners could soon have more room to work with when planning a granny flat. Western Australia is considering changes to the Residential Design Codes that would lift the maximum floor area for an ancillary dwelling from 70 m² to 90 m². Parking requirements and rear boundary setbacks are also part of the review. The changes are proposals, not current rules, but they could noticeably alter the way granny flats are designed on established residential blocks.
The WA Government’s announcement on the proposed granny flat changes confirms that consultation remains open until 26 February 2027.
What the Proposed Granny Flat Changes Could Include
| Proposed Change | What It Could Mean |
| Maximum Floor Area | Increase from 70 m² to 90 m² |
| Car Parking | Minimum parking requirements could be removed |
| Rear Setbacks | Reduced rear boundary setbacks proposed for lower-density areas |
| Planning Process | More compliant granny flats could avoid separate council planning approval |
| Current Status | Consultation is underway. The changes are not yet in force |
Why Another 20 Square Metres Could Change the Design
Twenty square metres does not sound enormous until it is added to a small dwelling.
At 70 m², every room competes for floor space. A second bedroom affects the living area. A larger bathroom takes room from storage. Corridors and door clearances also use space that never appears particularly generous on a floor plan.
A 90 m² ceiling would give designers more flexibility in deciding where that floor area goes. One household might want two comfortable bedrooms. Another could prioritise an accessible bathroom and wider circulation for an older family member.
Some owners may simply want a less compressed living area.
This does not mean 90 m² should become the default size. A smaller dwelling can still work very well when the layout suits its occupants and the block. The proposed change would provide another option rather than a new target everyone needs to reach.
That flexibility is especially relevant when looking at granny flat design in Perth, where block dimensions and existing buildings can differ substantially from one suburb to the next.
The Backyard Still Sets the Limits
A higher maximum floor area does not create extra land.
Established Perth properties often have several constraints already occupying the backyard. A patio may extend from the main house. There could be a pool, garage, shed, large tree or retaining wall. Underground infrastructure can further reduce the practical building area.
The proposed R-Code changes do not erase those conditions.
A useful early site review should identify:
- Existing buildings and structures that will remain.
- Sewer lines, easements and other services crossing the property.
- Access available beside or around the existing home.
- Ground levels that may affect construction.
- Boundary conditions relevant to the proposed location.
- Outdoor areas the household wants to retain.
This is often where the size of the future granny flat becomes clearer.
A homeowner may technically have enough land for a 90 m² dwelling, yet prefer a smaller footprint to preserve garden space or separation from the main house. On another property, the proposed setback changes may make a previously awkward portion of the backyard easier to use.
Parking Could Stop Dictating Part of The Layout
The proposal to abolish minimum car-parking requirements for granny flats deserves attention because parking consumes more space than the bay itself.
Vehicle access has to reach the parking area. On some properties, that can mean keeping a strip of land clear along the side of the house or arranging the backyard around a driveway.
Removing a blanket minimum would not stop homeowners from providing parking where it is useful. It would allow the design to respond to the occupants instead.
An older parent who no longer drives may have little use for a dedicated bay. A household near good public transport may also prefer to use that land as landscaping or private outdoor space.
Other households will still want parking, and their plans can provide it.
That distinction gives individual properties more room to respond to actual use rather than a standard assumption.
Rear Setback Changes Could Open Up Difficult Blocks
The WA Government has also proposed reducing rear lot boundary setbacks in lower-density areas.
This could affect how a granny flat is positioned, particularly on blocks where usable backyard depth is limited.
Moving a dwelling closer to the rear boundary could leave more separation between the granny flat and the existing house. That extra space may be useful for a courtyard, garden or a clearer pedestrian route.
It still requires careful planning. Privacy, windows, neighbouring properties and outdoor areas remain part of the broader design discussion.
The smallest permissible setback is not automatically the best location for a building.
Planning Approval Is Only One Part of The Process
One point that can become confusing when planning reforms are announced is the difference between planning approval and building approval.
The proposed reforms are intended to allow more compliant granny flats to avoid a separate council planning approval process. The WA Government has said that under the proposed changes, more developments could proceed with only a building permit required.
The distinction is easier to understand through the existing guide to planning approval vs building permit in WA.
Planning approval deals with whether a proposed development is acceptable for the property under planning controls. A building permit deals with the construction itself and the applicable technical requirements.
Current WA guidance also makes clear that granny flats which qualify for planning exemptions still require a building permit and must comply with applicable building requirements.
So, a simpler planning pathway should not be read as permission to build without documentation.
Good Drawings Become More Useful as Options Increase
A larger allowable floor area can create more design choices, but those choices still need to be tested against the site.
Plans establish room sizes and circulation. Elevations show height and the external relationship between buildings. Sections become useful where ground levels change or where floor and roof heights need closer attention.
Site plans also document the position of the new dwelling relative to the main house, boundaries and other property features.
That makes accurate residential drafting in Perth relevant well before construction begins. The drawings provide a practical way to test whether the preferred layout can actually fit the property while responding to the applicable requirements.
What Homeowners Can Do While Consultation Continues
There is little value in designing a project around a proposed rule as though it has already been adopted.
For now, Perth homeowners interested in a future granny flat can gather the information that will remain useful regardless of the final outcome. Check the property dimensions. Locate known services and easements. Decide which existing structures need to remain.
It also helps to think about the future occupant rather than starting with floor area.
Does the person need one bedroom or two? Would level access be useful? How much privacy is wanted between the two dwellings? Is outdoor space more useful than another internal room?
Those decisions often shape a successful plan more than an extra number on the allowable floor area.
Keep the Proposed Rules in Perspective
The move from 70 m² to a proposed 90 m² limit could give Perth households noticeably more freedom when planning ancillary accommodation. Removing mandatory parking and adjusting rear setbacks could also make some constrained blocks easier to work with.
None of those changes are final yet. Consultation closes on 26 February 2027, after which the proposed R-Codes still need to proceed through the relevant approval process.
Until then, homeowners should rely on the rules currently in force and treat the 90 m² figure as a possible future standard.
For drafting practices such as Domestic Drafting Service, the review is one of those regulatory changes that will need watching closely because its final form could influence how future ancillary dwelling plans are prepared across Perth.
About the Author
