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Weekly · Granny Flats

Granny flats in WA: what you can build today, what might change, and how to design one well

Editor, Atelier Cabin · Published 12 Nov 2026

WA's draft R-Codes would lift the granny-flat limit from 70 to 90 m². None of it is law yet. This guide covers what applies on your block today, what is only proposed, what a granny flat costs, and how to make a small backyard home feel generous. Comments on the draft close at 5pm on 26 February 2027.

Perth has granny flats on its mind. Domain's Spring Property Report 2025 found that "granny flat" had climbed to the second most-searched keyword among Perth buyers on its site, behind only "pool". Domain put the rise at about 59 per cent, and trade coverage of the same report gave 59.8 per cent. People want to know the same few things: what the rules are, what it costs, and how to fit a real home into 60 or 70 square metres.

The timing is good. On 24 October 2026 the State Government released draft changes to the Residential Design Codes (R-Codes), the rulebook for housing in WA, and several of them are aimed squarely at granny flats. Here's how to read them. For how WA compares with NSW, Victoria and New Zealand, see our earlier Weekly, Granny flats by the rulebook.

The rules today (current law)

In the R-Codes a granny flat is called an ancillary dwelling: a self-contained dwelling on the same site as a house. It can be attached to the house, built into it or stand on its own. Since 10 April 2024:

  • No planning approval is needed for an R-Code-compliant granny flat on residential land, whatever the lot size. You only need a building permit.
  • The size limit is 70 m² of internal floor area.
  • The old 350 m² minimum lot size has gone, and granny flats are allowed on grouped-dwelling and strata lots as well as single-house lots.
  • A parking bay is usually not required. The exception is in some densities and locations further from public transport ("Location B" in the R-Codes), where one bay is still needed.
  • It no longer has to match the design of the main house.

It still has to meet setbacks and the other deemed-to-comply standards, sit behind the street setback line, and leave the main house with its required open space. Exemptions don't apply everywhere, and some councils have their own local planning controls, so check with your local government before you commit.

What's proposed (not yet law)

The government's 24 October statement and the WAPC's consultation papers propose:

  • Raising the maximum internal floor area from 70 m² to 90 m². (The separate "small dwelling" category stays at 70 m².)
  • Dropping parking minimums for granny flats. Under the draft, no extra bay would be needed beyond what the main house requires. The Table of Changes notes an exception for granny flats outside the Perth and Peel regions.
  • Reducing the rear lot boundary setback in lower-density areas.
  • Exempting more granny flats from council planning approval, so more projects need only a building permit.
  • Letting councils allow granny flats larger than 90 m² through local planning policies.
  • Adding a design principle that a granny flat must "remain incidental to the primary dwelling".

These are drafts. The Department of Planning, Lands and Heritage says applications are still assessed under the current framework, and that any amendments are expected to start coming into effect from mid to late 2027, subject to consultation and approvals. Don't design to 90 m² today and expect it to be approved as exempt.

For context, other places are moving the same way. Victoria lifted its permit-free "small second dwelling" limit from 60 to 80 m² on 15 October 2026, though a building permit is still required. In New Zealand, the 70 m² building-consent exemption for granny flats was widened on 8 October 2026 to cover certain certified prefab panel systems.

What does a granny flat cost in Perth?

Honestly, we couldn't find a current, independent Perth-specific cost survey, so treat any single number with care. Here's what's published:

  • Builder list prices (one major WA builder, checked 30 Oct 2026): Summit Homes advertises base prices from $171,218 for a one-bedroom, $183,555 for a two-bedroom and $196,689 for a three-bedroom granny flat. These cover a steel-frame base build only. Summit says to allow about $15,000 for finishes on a 50 m² flat and about $20,000 on a 70 m² flat, with site works priced separately for each site.
  • A national average (older, not Perth-specific): realestate.com.au, quoting hipages cost guides in July 2025, put the average granny flat at $80,000 to $160,000. Site preparation, permits and finishes all add to that.

A word of caution on deposits. In August 2026 the ABC reported that Perth modular builder Bella Modular had stopped work, leaving customers who had paid large deposits uncertain about their projects. One had paid half the build cost upfront. Because the buildings were made off-site and the customers acted as owner-builders, builders' indemnity insurance didn't apply. Before you pay, ask what insurance covers you.

Granny flat or studio?

It's one of the most-searched questions, and in WA the answer depends on what's inside:

  • Granny flat (ancillary dwelling): self-contained, so you can live in it. It falls under the 70 m² rules above.
  • Shed, workshop or non-habitable studio (outbuilding): the R-Codes define an outbuilding as "an enclosed non-habitable structure that is detached from any dwelling". It can't be lived in.
  • A habitable studio without a kitchen, such as a home office or teenage retreat, sits somewhere in between. Some councils treat it as a "detached habitable room" under their local policies, so ask yours early.

Designing at 60, 70 and 90 m²

This is where we think most granny flats fall short. Catalogue plans tend to shrink a suburban house: a hallway, two small bedrooms and a living room facing the fence. Good small buildings start from the site instead.

  • Around 60 m²: design one generous room rather than three small ones. A tall ceiling, a long window seat, a kitchen along one wall and sliding doors that open the living space onto a covered outdoor room will make 60 m² feel far bigger than it measures.
  • At 70 m² (today's limit): this is enough for two real bedrooms or one bedroom plus a study. Spend the extra area on storage and a proper laundry rather than a hallway. Give the flat its own entry and outlook so neither household looks into the other.
  • At 90 m² (proposed): if it goes ahead, the extra space could allow a step-free layout for an ageing parent, a second bathroom, or a plan that could later be rented. Bigger isn't always better on a Perth block, though, because every extra square metre comes out of your garden and shade.

At every size, orient living spaces to the north, cross-ventilate for the afternoon breeze, keep west-facing glass small or shaded, and think about privacy from the main house. The 2024 change means a granny flat no longer has to copy the main house, which opens the door to buildings with their own character in timber, rammed earth or light-weight cladding.

How to have your say

Consultation on the draft R-Codes runs until 5pm (AWST) Friday 26 February 2027. On the Have Your Say WA R-Codes Review page you can:

  • fill in the short feedback form, a 5–10 minute survey on the key changes;
  • use the detailed feedback form to comment on specific provisions, and attach a written submission if you like; or
  • post a written submission to the Western Australian Planning Commission, Locked Bag 2506, Perth WA 6001.

The department is also running community pop-ups, and you need to register for them on the same page. In-person sessions are at Karrinyup (28 November), Midvale (2 December), Booragoon (3 December), Claremont (5 December) and North Perth (10 December), and there is an online drop-in on 8 December. Questions can go to the R-Codes team at [email protected] or 6551 8002.

The most useful submissions are specific. Tell them what you want to build, on what kind of block, and which rule helps or gets in the way.

This article is general information, not planning advice. Rules can change, and local planning schemes vary, so confirm with your local government before you design or build.

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