Granny Flat Guide Western Australia: Rules, Costs & Approvals (2026)

Key takeaways

WA calls them 'ancillary dwellings'. Regulated under the state-wide Residential Design Codes (R-Codes) plus local council policies.
WA has no fast-track CDC pathway like NSW. All ancillary dwellings need a building permit; some councils also require a planning approval.
Maximum size is 70m² on lots under 500m² and up to 100m² on larger lots. Generally permitted in R20+ zones.
Owner-occupier rule applies in most WA councils: one of the two dwellings must be owner-occupied. Pure investment dual-occupancy is generally not allowed.
Total build cost typically $80,000 to $200,000+ (design, fees, site works, construction, landscaping). Modular options available from $70K to $130K+ install.
Perth's rental market has been below 1% vacancy since 2022; rents of $380 to $600/week support strong yields on construction cost.

Verify with your council and the WAPC

Planning and building rules in WA vary by council and zoning. Always confirm requirements with your local council and the Western Australian Planning Commission before proceeding.

What is an ancillary dwelling in WA?

In Western Australia, what's commonly called a "granny flat" is officially an ancillary dwelling (sometimes secondary dwelling). It's a self-contained dwelling on the same lot as a primary residence, typically smaller than the main house, designed for a family member, carer, or tenant.

Ancillary dwellings are regulated under the Residential Design Codes (R-Codes), WA's state-wide planning framework, plus local council policies. The R-Codes set minimum lot sizes, maximum floor areas, and setbacks.

WA has no fast-track CDC pathway like NSW. All ancillary dwellings require a building permit, and some require a development application (planning approval) from the local council.

R-Code requirements

WA Residential Design Codes set the key parameters for ancillary dwellings. Requirements depend on lot size and zoning:

Lot size	Max ancillary dwelling size	Notes
Under 350m²	70m²	R20+ zone generally required
350m² to 500m²	70m²	Subject to setback and lot coverage rules
Over 500m²	Up to 100m²	Larger lots may allow larger dwellings

Key R-Code requirements:

Minimum lot size: Generally permitted in R20 and higher density zones. R20 typically corresponds to ~660m² for subdivision but lower for ancillary dwellings. Check your specific zone with your council.
Floor area cap: 70m² for most lots (under 500m²); up to 100m² for larger lots. Internal living area including bathroom and kitchen.
Setbacks: Must comply with side, rear, and primary-dwelling setbacks. These vary by zone.
Lot coverage: Combined coverage of all structures (main house + ancillary + outbuildings) can't exceed the maximum permissible for the zone.
Parking: One car bay may need to be provided in addition to those required for the main house.
Utilities: Must have a separate or separately metered electricity and water connection.

Always confirm with your specific local council (City of Perth, City of Stirling, City of Joondalup, etc.) as some have additional policies overlaying the state R-Codes.

Owner-occupier requirement

This is a critical difference between WA and NSW or QLD: in most WA councils, one of the two dwellings on the lot must be owner-occupied. Pure investment dual-occupancy is generally not allowed.

The registered owner must reside in the main house or the ancillary dwelling
Applies even if you're building the dwelling for a family member
Enforced through the planning approval and building permit conditions
Some councils may have exceptions, always verify

So WA granny flats best suit owner-occupiers who want to:

House a family member (elderly parent, adult child) on the same property
Generate rental income from the ancillary dwelling while living in the main house
Create multi-generational living arrangements

Approval process, building permit

Unlike NSW's CDC pathway, WA requires a building permit for all ancillary dwellings, processed via your local council or a registered building surveyor. The process:

Pre-application research. Confirm your lot's zone, R-Code, and whether your council has additional local policies. Check if planning approval is required in addition to a building permit.
Engage a designer or draftsperson. Architectural drawings demonstrating R-Code compliance. A draftsperson is usually sufficient for standard ancillary dwellings, you don't always need a full architect.
Submit development application (if required). Some councils require a DA before the building permit, particularly if the proposal triggers discretionary criteria. Processing: 30 to 60 days.
Submit building permit application. Lodge with your local council or a registered building surveyor. Include plans, specs, and a site plan showing setbacks. Processing: typically 10 to 25 business days.
Commence construction. Don't start without an approved building permit. Inspections required at footings, frame, completion.
Final inspection and occupancy. Final building inspection confirms compliance, then the ancillary dwelling can be occupied.

Costs of building a granny flat in WA

Costs vary significantly with size, finish, and site complexity.

Item	Typical cost range
Design and drafting	$3,000 to $8,000
Council fees (DA + building permit)	$2,000 to $5,000
Site works (slab, drainage, services)	$15,000 to $40,000
Construction (50 to 70m² ancillary dwelling)	$80,000 to $160,000
Landscaping and fencing	$5,000 to $15,000
Total estimated cost	$80,000 to $200,000+

Prefab/modular ancillary dwellings can reduce time and cost. Several WA-based suppliers offer complete modular units in the $70,000 to $130,000 range (plus site prep and installation). Ensure any prefab is pre-certified for WA building codes.

Rental income potential in Perth

Perth's rental market has been exceptionally tight since 2022, with vacancy rates consistently below 1% across most suburbs. Strong demand for ancillary dwellings as well as standard rentals.

Typical rents for a 1 to 2 bed ancillary dwelling in 2026:

Inner Perth (5 to 10km from CBD): $450 to $600/week
Middle ring (10 to 20km from CBD): $380 to $500/week
Outer suburbs: $300 to $420/week
Coastal suburbs (Fremantle, Cottesloe, Scarborough): $450 to $650/week

13–20%

Typical gross yield on construction cost: $400/week rent on a $100K to $150K build.

Before rates, insurance, and maintenance

Even allowing for expenses, returns can be compelling, especially given how tight Perth's rental market has been.

Popular areas for granny flats in Perth

The best Perth areas for ancillary dwellings combine:

Suitable zoning: R20+ with adequate lot sizes
Strong rental demand: Near universities, hospitals, train stations
Owner demographics: Higher rates of long-term owner-occupancy

Popular areas: Morley, Balga, Midland, Victoria Park, Belmont, Cannington, and Gosnells in the middle ring; coastal suburbs like Fremantle, Hamilton Hill, and Beaconsfield; established inner suburbs like Mount Lawley, Northbridge, and Bayswater.

Practical tips for WA granny flat owners

Check your title first: Some properties have title restrictions (developer covenants) prohibiting secondary dwellings. Your conveyancer or Landgate can check before you invest in plans.
Strata title: If your property is in a strata scheme, separate strata company approval may be required in addition to council approval.
Tax implications: Rental income is taxable. Consult an accountant about depreciation, which can offset a significant share of income in early years.
Insurance: Update building insurance to cover the ancillary dwelling and consider landlord insurance for the rental.
Tenancy laws: As a landlord, you're bound by the WA Residential Tenancies Act. See Renter's Rights in WA for the obligations from the tenant side.

Resources

Western Australian Planning Commission (WAPC): wa.gov.au
Department of Planning, Lands and Heritage WA, R-Codes: dplh.wa.gov.au
Landgate, property title and land information: landgate.wa.gov.au
Building Commission WA, building permits and standards: commerce.wa.gov.au

Want one-on-one help with this stage?

If you’ve done the reading and want a real human to talk it through, we’ll find the right specialist for your situation, whether that’s an agent, broker, accountant or conveyancer. Free, no commitment.

Get matched in 24 hours

Common questions

Why does WA require an owner-occupier in most councils?

It's a planning policy choice rooted in neighbourhood-character objectives. The condition is enforced through the planning approval and building permit. The registered owner must reside in either the main house or the ancillary dwelling; pure investment dual-occupancy is generally not permitted in WA.

What's the maximum size for an ancillary dwelling in WA?

70m² on lots under 500m². Lots over 500m² may permit up to 100m². The cap is the internal living area including bathroom and kitchen. Verandahs and external storage typically don't count, but confirm with your draftsperson.

What R-zone do I need to build a granny flat?

R20 or higher density zones are generally required. R20 typically corresponds to a minimum lot size of around 660m² for subdivision but lower for ancillary dwellings. Check your specific zone with your local council.

Do I need a planning approval as well as a building permit?

Sometimes. Some WA councils require a development application (planning approval) before the building permit, particularly if the proposal triggers discretionary assessment. Many councils don't if you comply with the R-Codes. Check with your council early in the process.

Can I rent out the ancillary dwelling on Airbnb?

Short-stay rentals are increasingly regulated in WA, especially in metropolitan areas. Some councils require additional approvals for short-stay use. Always check council rules and consider whether it conflicts with the owner-occupier requirement.

What yields can I expect in Perth?

Rental income on a 1 to 2 bed ancillary dwelling typically runs $380 to $600/week in Perth (higher near the coast). At $400/week on a $130K build, gross yield is roughly 16%. Even after expenses (rates, insurance, maintenance), that's well above standalone investment property returns.