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Granny Flat Size Guide – The Ultimate Resource

When building a granny flat, your budget and local regulations will determine what is allowed. So, what is the maximum size a granny flat can be?


Depending on your local Council, the regulations on how big your granny flat can be change. Generally speaking, the minimum size you can build a granny flat is 40 square metres. The maximum size you can build a granny flat ranges anywhere from 50 to 100 square metres.


Today I will discuss how big a granny can be for you.


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I will cover the size the bedrooms, bathrooms and kitchen should be.  Plus discuss the average size of a granny flat deck. And how you can make it as big as you like! So lets get right into it.


How Big Should a Granny Flat Be?


A granny flat should be designed to suit both your personal style, and your budget. After all, it is a smaller version of your main home and needs to fit in and flow well with your primary dwelling.


However, at the same time, you do need to stick to certain regulations here:


  • Queensland – 80 square metres.
  • Although, in Brisbane, you can build a granny flat a maximum of 70 square metres but with no more than two bedrooms. So, you can try speaking directly with your local Council to find out your exact restrictions, as they do change between Councils’. See detailed QLD rules
  • Victoria – 60 square metres, and they are called a “Dependant Persons Unit” (DPU), so must be movable. Similarly to Queensland, the regulations vary on size depending on your Council. See detailed VIC rules
  • New South Wales – From 60 square metres – 100 square metres. The former is a Complying Development, and the latter must be approved by submitting a Development Application. See Detailed NSW rules
  • South Australia – 60 square metres OR 70% of the total floor area of the primary dwelling (whichever is less). See detailed SA rules
  • Tasmania – 60 square metres OR 30% of the total area of the main home (the lesser). See detailed TAS rules
  • Western Australia – From 70 square metres – 100 square metres depending on your local Council. Rural areas are more likely to be flexible. See detailed WA rules
  • Northern Territory – Metropolitan areas, such as the city of Darwin, has more strict limits, with the floor space limited to 50 square metres. Again, rural areas are possibly more lenient. Your local Council may allow up to 80 square metres.
  • Australian Capital Territory – 90 square metres. It is worth mentioning that the ACT also has a minimum size limit for granny flats of 40 square metres. See detailed ACT rules



What Size Should Granny Flat Bedrooms Be?


This is not regulated for granny flats, and they can vary in size and shape. Standard bedroom sizes average around 3m x 3m However you can still fit a double bed in a smaller space than this. A bedroom is a private space for personal use, storage and rest. It should be designed to suit the owner occupiers or tenants.


They do however, require:


  • An access door
  • Electrical fittings
  • Windows – To comply with the Building Code of Australia (BCA), a bedroom must have enough windows to provide adequate ventilation and natural light. The BCA states the bedroom must have windows that are equal in size to;
  • A minimum of 10% of the bedrooms floor area
  • Ventilation of only 5%.
  • Smoke alarms – As per the BCA, it is law that smoke alarms must be fitted to all bedrooms.


Also, keep in mind that anything less than:


  • The size of a double bed, plus room for an egress (the exit) is not practical.


When planning the layout of a bedroom, imagine all possible furniture arrangements. It is a basic requirement that a minimum of 700mm should be left to allow room for comfortable egress between spaces, to ensure:


  • The placement of the bed and bedside tables do not impact on the egress and the opening of doors.


So, factoring all of this in equals a total of 2.77sqm. If any bedroom is smaller than 2.77sqm it will be extremely tight for a double bed and exiting can be hard.


This will irritate and even put off tenants, possibly impacting your rental return.


Standard bedroom sizes are:


  • Master bedroom (Including built-in wardrobe and ensuite) – 12.25sqm
  • 2nd / 3rd bedroom – 9sqm
  • 4th bedroom (Often used as a study) – 7.84sqm


Also keep in mind that a bedroom does not require a wardrobe, but they are expected. Consider built-in wardrobes in all your bedrooms and space saving designs.


What Size Should Granny Flat Bathrooms Be?


Again, this is not controlled. However, 2m x 2m will be a bare minimum to fit all you need. The floor space of your bathroom needs to fit:

  • Shower cubicle (generally/commonly 900 x 900mm) However you can get “thinner” showers
  • Toilet
  • Vanity unit


Smaller bathrooms are usually 1.5m x 2m (3sqm).


Space and budget permitting, you can choose to have a larger bathroom as big as 3.2 x 2.5m (8sqm). However in a granny flat a bathroom this big is not usually required. The best choice is, if possible, to go for a bigger space as its going to be useful to wind down and relax, especially if you are planning it as a teenagers retreat.


What Size Should A Granny Flat Kitchen Be?


Most kitchens need at least 3m of bench space to fit common appliances. This is not regulated though and a kitchen is also not required in all granny flats.
Average house kitchens take up 3.2 x 4m (12.8sqm). Though, if your budget or size does not allow for this, you can create a much smaller kitchenette.


If your granny flat is occupied by a family member, they can often use your kitchen in the main home. However, if you are planning on renting out the granny flat, consider putting in a kitchen/kitchenette.


After all, for many, the kitchen is the favourite part of their home. And if you want some inspiration about granny flat kitchens see this article I put together.


Regardless of which design you choose the following standards should be met when designing your kitchen/kitchenette:


  • Windows – A source of natural lighting and adequate ventilation
  • Ease of access – Keep the distance you are travelling between your sink, stove, and fridge to a minimum
  • Space to move – Keep a good balance between the walking distance so you don’t feel cramped
  • Make maximum use of work surfaces and storage spaces – Whilst using minimum floor space.


Average Size of a Granny Flat Roof


A granny flat roof is restricted to a height of 8.5m by most councils. Meaning, to be compliant with regulations, the maximum allowable height for a granny flat is 8.5m tall. It is worth noting that the roof space is different to your floor space and having a larger roof won’t be an issue for room required for the eaves underneath.


This is measured from:


  • The vertical distance of the existing ground


  • The highest point of the building.


It excludes:


  • Flagpoles.
  • Antennas.
  • Communication devices.
  • Satellite dishes.
  • Masts.
  • Chimneys, flues, and the like.


Once the height of the granny flat begins exceeding 3.8m, regulations such as setbacks begin to apply.


For specific details; feel free to read up on Granny Flat Height Restrictions.


Average Size of a Granny Flat Deck


Attaching a deck to a granny flat is a way to legally increase your allowable floor space. That’s right, you do not have to be restricted by the regulations set by your local Council. And the deck can be very large. As long as you don’t impose on strict guidelines set out by your local council.


You can legally attach various structures to your granny flat to make it larger.


So, when attaching a deck, all you are restricted by is your yard space and setbacks, and your budget.


The average size of a deck is roughly 30sqm, quickly taking your granny flat from a possible restriction of 60sqm to 90sqm of outdoor living space.


For more information about using decks to make your granny flat bigger see these examples.



The maximum size a granny flat can be ranges from 50 to 100 square metres, depending on your local Council. However, if you wish to build something bigger than your local Councils’ regulations, you can always try speaking to them directly.


You never know, they may be feeling generous that day. Another option is to increase your floor space by adding a deck. With an average size of 30sqm that does not count as part of your floor space, this adds extra room to your granny flat. Keep in mind that the ACT has a minimum regulation on granny flats, being 40sqm.


You will realise this is fair enough when I discuss the standard size of the rooms below. Although none of these sizes are regulated, the standard sizes will help you build a more comfortable granny flat.


For a bedroom, anything less than the size of a double bed, plus room for an egress is not practical. This is 2.77sqm.


Standard sizes are:


  • Master bedroom (Including built-in wardrobe and ensuite) 9-12sqm
  • 2nd / 3rd bedroom – 9sqm


A bathroom needs to be big enough to fit a:


  • Shower cubicle (generally 900 x 900mm)
  • Toilet
  • Vanity unit


Standard sizes are:


  • Smaller bathrooms – 1.5m x 2m (3sqm)
  • Average bathrooms – 2m x 2m (4sqm)
  • Larger bathrooms – 3.2 x 2.5m (8sqm).


A kitchen is not required in all granny flats but should be considered. A standard size for your kitchen, space and budget allowing, is 3.2 x 4m (12.8sqm). Although, you can create a much smaller kitchenette.


Just design everything in your granny flat to suit your style and budget, whilst meeting your regulations for approval.