70m² Granny Flats in Perth: The Hidden Rule that can Still Trigger Planning Approval
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- 1 day ago
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A 70m² granny flat can sound like a simple approval pathway for Perth homeowners. Under Western Australia’s updated ancillary dwelling rules, a compliant granny flat may avoid planning approval if it does not exceed 70m² and meets the relevant deemed-to-comply requirements.
But there is one important detail many homeowners miss: 70m² is not the only rule.
For homeowners in Canning Vale, Gosnells, Thornlie, Southern River, Armadale, Willetton, Melville, Cockburn, Canning, Belmont, Bayswater, and surrounding Perth suburbs, this is where professional drafting advice becomes essential.
Quick Answer: Can a 70m² Granny Flat Skip Planning Approval in Perth?
A 70m² granny flat in Perth may not need planning approval if it meets all relevant R-Code and local planning requirements. However, planning approval may still be required if the design fails one or more deemed-to-comply standards.
The most common hidden trigger is usually setback compliance. Even if the granny flat is 70m² or smaller, it may still need planning approval if it is positioned too close to a boundary or does not meet the local area setback rules.
A building permit is also still required before construction. Planning approval and building approval are not the same thing.
The Hidden Rule: 70m² is Not the Only Test
Many Perth homeowners focus on the 70m² limit because it is the easiest number to remember. But the more important rule is this:
Your granny flat must be fully deemed-to-comply.
That means the design must satisfy more than just the maximum floor area. It also needs to comply with requirements that may include setbacks, site cover, building height, outdoor living area, privacy, access, parking, heritage conditions, and local planning scheme rules.
For example, a proposed granny flat may be exactly 70m², but if it sits too close to the rear or side boundary, it may still require planning approval. Another design may fit within the backyard but create overlooking issues for a neighbouring property. A different block may have a sewer easement, retaining wall, patio, shed, or undocumented addition that affects where the granny flat can go.
This is where early architectural design and drafting in Perth can help confirm whether the layout suits the site before plans are finalised.
7 Common Reasons a 70m² Granny Flat Still Needs Planning Approval
1. The setbacks are not compliant
Setbacks are one of the most common reasons a granny flat may still need planning approval. The granny flat must be positioned correctly on the lot in relation to side, rear, and sometimes front boundaries.
This can be challenging on smaller Perth lots, narrow blocks, rear-loaded properties, corner lots, or homes with existing patios, sheds, pools, retaining walls, or extensions.
2. The block has heritage or character controls
Some Perth properties are affected by heritage listings, character area controls, or local planning policies. This is especially relevant in older suburbs or areas with established streetscapes.
If your property is in a heritage area, planning approval may be required even where the granny flat is under 70m².
3. The granny flat affects open space
A granny flat cannot simply take up any unused part of the backyard. The overall property may still need to satisfy open space, outdoor living area, and site coverage requirements.
This is important for established Perth homes where the rear yard already includes patios, sheds, alfresco areas, pools, workshops, or previous additions.
4. The design creates privacy issues
Visual privacy can become a planning issue when windows, raised floors, balconies, outdoor areas, or upper-level elements overlook neighbouring properties.
Even a compact granny flat can create privacy concerns if it is positioned poorly or designed without considering adjoining homes.
5. The site has easements or access restrictions
Many Perth blocks include sewer lines, drainage easements, restricted side access, retaining walls, or difficult construction access. These constraints can affect where a granny flat can be placed and whether the design remains compliant.
6. Existing structures are not accurately documented
Older homes often have additions that may not be shown clearly on previous plans. A patio, shed, carport, retaining wall, or extension can affect site cover, setbacks, access, and available building space.
Accurate existing condition drawings help identify these issues early.
7. The property is not a straightforward residential lot
Some properties may be affected by rural zoning, bushfire-prone area requirements, strata rules, special control areas, coastal conditions, or local planning scheme provisions.
This is why a site-specific review is more reliable than relying on general advice.
Planning Approval is Different from a Building Permit
One of the biggest misconceptions is that “no planning approval” means “no council process”. That is not correct.
Planning approval checks whether the proposed granny flat is acceptable from a planning perspective. This can include land use, zoning, setbacks, privacy, site layout, open space, and local planning rules.
A building permit checks whether the building documentation meets construction and technical requirements. This includes drawings, structural information, building code compliance, health and safety requirements, and other technical details.
Even if your granny flat does not need planning approval, you will still generally need a building permit before construction begins.
That means professional drawings are still required. A professional building drafting service helps prepare the technical drawings needed for building permit assessment, even when planning approval is not required.
Why Your Perth Block Matters More Than the 70m² Limit
Two homeowners can both want a 70m² granny flat, but their approval pathways may be completely different.
A larger block in Canning Vale with clear rear access may be relatively straightforward. A narrow block in an older Perth suburb with heritage controls, sewer easements, retaining walls, and existing structures may need more careful planning.
Before starting detailed drawings, Perth homeowners should check:
The property zoning and R-Code density
Side, rear, and front setbacks
Existing structures on the property
Sewer, drainage, and easement locations
Site cover and open space
Outdoor living area requirements
Privacy and overlooking
Access for occupants and construction
Heritage, bushfire, coastal, or special control overlays
Whether planning approval is required before the building permit
This early review can help avoid redesigns, delays, and unexpected application requirements. If the property may later be subdivided or developed further, a subdivision drafting service can help owners think about the granny flat in the context of longer-term site planning.
How Domestic Drafting Service Helps Perth Homeowners
Domestic Drafting Service helps Perth homeowners prepare clear and practical drafting documentation for residential projects, including granny flats, additions, renovations, new homes, and building permit applications.
For a granny flat project, professional drafting can help with:
Site measure and existing condition drawings
Concept layouts
Granny flat floor plans
Elevations and sections
Site plans
R-Code and setback checks
Council-ready drawings
Building permit documentation
Consultant coordination where required
To check what is possible on your block, contact Domestic Drafting Service before committing to final granny flat plans.
Frequently Asked Questions
Can I build a 70m² granny flat in Perth without planning approval?
Possibly. A 70m² granny flat may avoid planning approval if it meets the relevant deemed-to-comply requirements, including setbacks and local planning rules. If it does not comply, planning approval may still be required.
What is the hidden rule that can still trigger planning approval?
The hidden rule is full compliance. The granny flat must meet more than the 70m² size limit. Setbacks, site cover, privacy, height, access, zoning, and local planning requirements can all affect whether approval is needed.
Do I still need a building permit for a granny flat in WA?
Yes. Even if planning approval is not required, a building permit is still generally required before construction can begin.
Can a granny flat be rented out in WA?
Yes, WA rules allow ancillary dwellings to be used by relatives, friends, or tenants under a rental agreement, subject to the relevant requirements.
Who can prepare granny flat drawings in Perth?
A residential drafting service can prepare concept plans, site plans, elevations, sections, council drawings, and building permit documentation for a granny flat project.
Author Bio
Jayden Robinson is the Co-Director and Drafting Manager at Domestic Drafting Service, with a focus on functional residential design and practical drafting documentation for Perth homeowners. Learn more about Jayden and the team on the Domestic Drafting Service: https://www.domesticdraftingservice.com.au/team
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