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A guide to Granny Flats

Posted 30 June 2022


From pool house to retirement plan, from property investment to teen-scene hangout; the granny flat product is diverse and flexible and is a smart and affordable way to use up that patch of land on your block you've been wracking your brain about.

How much does a granny flat cost?

What sizes do they come in?

What is the process of building a granny flat?

We've put together our guide to understanding the steps you take when choosing to build this chameleon of a home structure.

If you're thinking about building a granny flat in Perth, download our guide to get started.



Can I build a granny flat on my property?

WA’s granny flats regulations run under the Planning and Development Act 2005, and are fairly lenient compared to other states.

Similar rules apply in some circumstances:

  • Only one granny flat can be built on each lot
  • If you build a granny flat, you are not allowed to subdivide your lot (unless it is allowed under the local planning scheme)
  • A minimum lot size of 450sqm (unless your local Council states otherwise)

So, if planning on building a granny flat, you need to understand the regulations that apply to your area, including:

  • Minimum lot size
  • Maximum floor area
  • Parking requirements

The Residential Design Codes shows the key regulations, but these can vary between Councils’.

Factors I need to consider when building a granny flat?

  • Size – While granny flats are typically small spaces, they are not all that way. If you have the space, you can have 3-4 bedrooms. However, these will cost more as they take more time and use more materials. If you add more rooms, you add more money.
  • Design – Granny flats have both standard and custom-made designs. You’ll spend more on something custom-made.

  • Additional tasks – Quotes are based around things such as easy access to a site. The price will rise if the area needs to be prepared prior to building the granny flat. This can be anything from excavation to clearing obstructions (i.e. trees).
  • Rates – When you talk to your Council, ask if your granny flat will impact your rates. Your rates are determined on the rental value of your property, so may increase.
  • Fees – When you talk to your Council, ask what the fees (i.e. permits) are for your granny flat. You need to be aware of additional charges ahead of building, so you can budget for them.
  • Servicing – You may need to install new sub-meters for electricity, gas, and water, depending if you plan to rent out the granny flat. Contact gas and electricity distributors, and the Water Corporation. Discover what options are available and decide which suit you best.
  • Installation fees – You are also likely to need a licensed plumber or electrician to install the new services.

What is the maximum granny flat size in WA?

SPP 3.1 limits granny flats to a maximum floor area of 70sqm. However, this may differ across local Councils’. 


*FAQ information supplied by

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