If you have started looking into building a granny flat, you have probably come across a few different numbers: “60 square metres,” “35 square metres,” or “up to 25% of the main house.” It is easy to see why many homeowners feel uncertain before they even reach the design stage.
The granny flat sizing rules sit across several documents, and the wording is not always written with everyday families in mind. The core idea, however, is relatively straightforward once it is broken down.
In this post, we will focus on the most frequently asked questions: what size can your granny flat be in NSW, and what size should it be for real, comfortable living? We will explain the legal maximum, the practical minimum, and how a trusted Sydney builder like Brickwood Homes can help you choose a size that works for your block, your budget, and your plans.
Why Granny Flat Size Requirements Feel Confusing
In NSW, granny flats (officially called “secondary dwellings”) are governed by several different documents that work together:
- The Housing State Environmental Planning Policy (Housing SEPP) sets the maximum internal floor area and approval framework
- The Building Code of Australia (BCA) establishes structural, safety and functional standards
- The Apartment Design Guide (ADG) provides guidance on minimum room sizes and liveability
When you read these in isolation, they can appear to contradict each other. One talks about maximum area, another about minimum room sizes, and a third about clearances and circulation space. As a homeowner, you do not need to know every clause. What you do need is a clear understanding of the maximum internal floor area you are allowed and the smallest size that still feels like a proper home and passes certification.
Finding that balance is a large part of what our design team at Brickwood Homes does when we plan granny flats in Sydney for local families.
The Maximum Size: 60 m² of Internal Floor Area
Under the current Housing SEPP, the maximum internal floor area for a secondary dwelling in NSW is 60 m² in most standard residential zones.
Here is what that means in practice:
What Counts Toward the 60 m² Limit
The 60 m² limit applies to enclosed, habitable space inside your granny flat:
- All bedrooms
- Living and dining areas
- Kitchen space
- Bathroom and laundry areas
- Internal hallways
- Built-in storage and cupboards
Basically, if it is inside the external walls and under the roof, it counts toward your 60 m².
What Does Not Count Toward the 60 m² Limit
External and semi-outdoor areas are completely separate from your 60 m² internal floor area:
- Open or covered patios
- Timber or composite decks
- Covered alfresco dining areas
- Verandahs and pergolas
- Garages and carports (in most configurations)
This means you can add outdoor living space without eating into your 60 m² allowance. A well-designed 60 m² granny flat with a generous deck can deliver significantly more total usable space.
In some council areas, you may also see a guideline referring to the granny flat being limited by a percentage of the main dwelling’s floor area (for example, “60 m² or 25% of the main dwelling, whichever is greater”). In practice across NSW, the working number is up to 60 m² of internal living space for your granny flat, whether it is built beside your home, behind it, or above another structure.This size cap is part of what makes building a detached secondary dwelling such a practical way to add housing on an existing block without moving into multi-unit development territory.
The Minimum Size: Why 35-40 m² Is the Practical Lower Limit
The minimum side of the equation is less direct. You will not find a line in the Housing SEPP that says, “A granny flat must be at least X square metres.” Instead, the ADG and BCA provide minimum room sizes and functional clearances that every granny flat must meet.There is no single minimum total floor area written specifically for granny flats in NSW.
The minimum size is determined by whether the design can fit all required rooms, meet minimum room dimensions, and provide safe, functional circulation space.
Minimum Room Requirements
The Apartment Design Guide and common design practice in NSW use these benchmarks:
- Main living room: around 12 m² or more
- Main bedroom: around 10 m² with a typical minimum width of 3 m
- Kitchen: enough depth and width to safely fit cooktop, oven, sink, fridge and bench space
- Bathroom/laundry: space to comfortably fit fixtures and allow doors to open without clashing
Once you place real furniture into those spaces by adding a bed, sofa, dining table, storage, and clear walking paths, the total area adds up quickly. When we design to these standards while keeping the granny flat feeling like a genuine home rather than a cramped cabin, the smallest one-bedroom designs we see certified and used comfortably usually sit in the 35-40 m² range.
This is why many certifiers and designers refer to around 35 m² as the smallest practical size for a self-contained granny flat, even though it is not a strict minimum written into the SEPP.
What Needs to Fit Inside
Think about what a functional granny flat requires:
- A living and dining area where someone can sit, relax and share a meal
- One bedroom with space for a bed and a wardrobe
- A bathroom with a shower, toilet and vanity (often combined with a laundry)
- A compact but safe kitchen with room to cook and store everyday items
- Hallways, doors and circulation space
Once you give each of those areas enough room to be usable, you move quickly beyond 25 or 30 m². Very small designs can look clever on paper, but when an assessor checks clearances and dimensions against BCA and ADG expectations, they often struggle to meet the requirements.This is where well-considered small granny flat floor plans make all the difference between a design that passes certification and one that does not.
Popular Granny Flat Size Ranges That Work
At Brickwood Homes, we design and build granny flats across Sydney and surrounding areas. Certain size categories come up regularly because they offer a good balance between comfort, budget, and approvals.
Compact One-Bedroom: 35-45 m²
This size range works well for:
- Adult children who want semi-independent living
- A single tenant or couple
- A quiet retreat for work, guests or hobbies
These designs rely on careful planning. Storage often needs to be built in, and window placement is important to avoid the home feeling closed in. This is where thoughtful granny flat floor plans matter more than simply chasing an extra square metre.
Comfortable One-Bedroom: 45-55 m²
A slightly larger footprint offers:
- A more generous living and dining space
- A kitchen layout with better bench and storage options
- Improved space for wardrobes and linen storage
For many homeowners, this is the “comfortable for the long term” option, especially when the granny flat is intended for parents or long-term tenants who appreciate a bit more breathing room.
Full-Size Two-Bedroom: 60 m²
At the top of the allowed size bracket is the full 60 m² design. This is where well-planned 2 bedroom granny flat floor plans are most effective. With the extra area, you can generally provide:
- Two proper bedrooms with wardrobes
- A shared bathroom, often with a combined laundry
- A full kitchen, such as an L-shape or galley configuration
- A comfortable living and dining zone that does not feel crowded
Our Tokyo design is a good example of how a 60 m² granny flat can be laid out to feel like a complete small home. You can view it here: Tokyo Granny Flat Design.
How Size Influences Approvals
Size is not only a comfort decision; it is also an approvals decision. To be approved as complying development (the faster path with a private certifier), your granny flat must:
- Be no more than 60 m² of internal floor area
- Be on a property that meets minimum lot size and zoning rules (often at least 450 m² for standard residential zones)
- Comply with setback, height and private open space requirements
- Maintain only one main dwelling and one secondary dwelling on the lot
If any of these conditions are not met, your project may still be possible, but it may require a development application through your local council. This is often when homeowners ask about council approval for granny flat projects and whether their site can still support a secondary dwelling.
The answer depends on your zoning, your block size, existing structures, and how close the design comes to the relevant limits. If you have not already read it, our detailed guide on regulations for granny flats in NSW looks more closely at zoning, setbacks and open space requirements.
For the official wording, you can review the NSW Planning information on secondary dwellings here.
Choosing the Right Size for Your Household
Once you understand the rules, the next step is to think about what is suitable for your situation. Some helpful questions to consider:
- Who will live in the granny flat over the next five to ten years? Short-term rental has different needs compared with a long-term home for parents or adult children.
- How important is privacy and separation? A compact one-bedroom near the garden may suit a teenager or single tenant. For multi-generational living, two bedrooms and a more generous living area can make daily life more comfortable.
- What does your block naturally support? Narrow or sloping sites may favour certain footprints. This is where custom design and smart small granny flat floor plans can turn a challenging block into a well-used space.
- What is your budget and expected return? Building right up to 60 m² will cost more, but it can also offer more flexibility and potential rental appeal in the longer term.
As a trusted, local granny flats builder in NSW, our role is to listen first and then translate your answers into a design that works and complies. You should not have to interpret every line of planning policy; that is part of the service we provide.
Work With a Local Builder Who Understands the Rules
Building a granny flat is a meaningful project, and the rules around size can seem complex at first glance. Once they are broken down, the picture is clearer, and you can make calculated decisions based on your current needs and future goals.
Brickwood Homes designs and builds granny flats across Sydney and the surrounding areas. We work regularly with the same councils, certifiers and regulations, so we understand how to balance clear compliance with thoughtful design.Whether you are just beginning to explore ideas or comparing different granny flat floor plans, we can help you understand what will work on your property, from a compact studio-style layout through to a generous 60 m² home. If you would like to discuss options, including custom designs tailored to your site, you are welcome to get in touch with our team about your next steps..
