Interest in granny flats has surged as families look for flexible living and rental income without moving house, and home building designers are fielding more questions than ever.
The short answer: planning approval vs building permit
In most residential zones across Western Australia, a compliant ancillary dwelling (granny flat) no longer needs development (planning) approval. The State’s 2024 R-Codes reform expanded the list of works that are exempt when they meet the deemed-to-comply standards. You still need a building permit from your local government before construction.
What is a granny flat under the R-Codes?
An ancillary dwelling is a self-contained home on the same lot as an existing single or grouped dwelling. It can be attached, integrated or detached, provided it meets the R-Codes standards. The core definition and assessment guidance sit in Clause 5.5.1 and the Explanatory Guidelines.
The 70 m² rule, made clear
The maximum internal floor area is 70 m². That figure is measured to the finished internal walls and excludes a garage, so you don’t lose floor space to vehicle storage. Keep the design within 70 m² and tick the other deemed-to-comply boxes and you’re on the fast track for exemptions from planning. If you’re chasing a coastal aesthetic or courtyard plan for new home design Mandurah, this cap is usually where smart planning and cabinetry make the difference.
What changed in 2024 (and why it matters)
The reforms removed the old minimum 350 m² lot size and opened the door for ancillary dwellings with grouped dwellings and on strata lots, provided the proposal meets the R-Codes. That shift is aimed at unlocking small and medium sites for gentle density. It’s a material easing of red tape for owners who previously missed out simply because their lot was a whisker under 350 m².
You still need a building permit
Skipping planning doesn’t mean skipping safety and compliance. A permit authority must decide a certified building permit application within 10 business days, or 25 business days for uncertified. Your designer, engineer and energy assessor will prepare the documents to hit those timelines. If you’re bundling your granny flat with other work, ask about certified pathways to keep things moving. Teams that deliver residential design services Perth wide work to these statutory timeframes every week.
Parking, setbacks and the fine print
Granny flats must still satisfy the usual R-Codes standards for siting, privacy and access. Parking is a common question: under the updated settings, ancillary dwellings often require no additional bay, especially in well-located areas, but your specific site and local policy can change the answer. Heritage places and special control areas are different too; development approval may still be needed in those cases even if the design meets the R-Codes. If you want a second opinion before lodging, speak with the best home designers near Mandurah and they’ll flag any local quirks early.
Approvals at a glance
| Approval or check | Needed for a compliant granny flat? | Notes |
| Development (planning) approval | Usually not required | Exempt when the R-Codes apply and all deemed-to-comply provisions are met; exemptions don’t apply on heritage places or where a local scheme says otherwise. |
| Building permit | Always required | Certified: 10 business days; Uncertified: 25 business days. |
| Energy efficiency | Mandatory | WA moves to NCC 2022 energy provisions for houses from 1 May 2025; design for 7-Star early. |
The exemption basis is set in the Planning Regulations (Clause 61) and the 2024 R-Codes updates, while building-permit timeframes come from the Building Act. The energy date is confirmed by NatHERS and state guidance.
Designing to the 70 m² limit without compromise
Well-proportioned living, a galley kitchen, a combined laundry cupboard and a compact bathroom can fit neatly within the cap. Aim for generous glazing to the main living area, keep circulation tight, and use built-in storage to free up floor area. A breezeway or covered alfresco can carry a lot of weight for day-to-day living in WA’s climate, which is handy when you want the plan to feel bigger than it reads. For projects near the estuary, a local home design company Mandurah will also factor in glare, sea breeze and corrosion resistance in the specification.
When planning approval may still apply
Tick the R-Codes and you’re typically exempt, but there are still tripwires. Heritage listing, special control areas, local variations, and proposals that seek discretion (because they don’t meet a deemed-to-comply standard) can bring planning back into play. If you’re unsure, ask for written confirmation from the duty planner before you pay fees or order surveys. That quick check saves rework later and keeps momentum for affordable home designers Mandurah seeking predictable lead times.
A practical path to approval
Start with a feature and contour survey, service checks and a site measure. Lock the plan to 70 m² internal, sketch elevations that sit comfortably behind the street setback, and check overshadowing and privacy. With that done, lodgement is straightforward: CDC from your building surveyor, engineering, truss/steel specs and energy report. If the build is bundled with a main-dwelling renovation, stage the paperwork so the granny flat can start on schedule. A studio that reads as part of the original home will always show better and rent easier, something seasoned home building designers keep in mind at concept stage.
Local help
Coastal air, canals and sandy soils add a few wrinkles to footing systems, material choices and maintenance schedules. A practice that knows Mandurah and the Peel Region can shortcut a lot of back-and-forth with practical detailing that suits the site. If you’re weighing quotes, ask about recent approvals and lead times, not just price.