What Are the Costs of Building a Granny Flat? 

There are a range of costs you need to be aware of when building a granny flat. The design you choose has a significant impact on the cost through your chosen size, materials and bedroom number. Getting approvals in the form of planning and building permission add to the overall price. Then there are miscellaneous costs such as utilities and furnishings, which also make an impact. Learning about all of these is important for proper budgeting and a successful granny flat build. Here at Granny Flats WA, we’ve guided many Western Australians through the process of building their dream granny flat. We pride ourselves on transparency, so here are the costs we highlight with our customers before they start building.

Granny flat building costs 

The main factor affecting the cost of the granny flat building process is the granny flat design. Granny flat design entails everything from the layout of the granny flat to the features contained within it. You should be aware of how various design factors affect building costs to plan your finances effectively. When you are deciding on a granny flat design, you decide how much customisation to include. If you’re creating something more bespoke and intricate, it could drive costs up. The design factors affecting granny flat building cost are size, layout, bedroom number, materials and land preparation.


Within design, size is one of the most important things to take into account. Granny flat sizes vary and correspond to the amount of building materials required. If you’re building a larger granny flat, then that will mean more materials and a greater building cost. Make sure you’re building a granny flat that isn’t too large for your budget.


The layout determines how the different features in a granny flat are arranged. Open plan layouts have less separation between rooms and areas in the granny flat, minimising costs. Closed-plan layouts include extra walls and more points of separation, causing the price to rise. Some people opt for cost-saving designs by converting their garages to granny flats.

Number of bedrooms

With a granny flat, more bedrooms often resulting in a more expensive granny flat. A studio granny flat or a one-bedroom granny flat often costs less to build since fewer rooms leads to a simpler build. Conversely, a granny flat with two, three or more bedrooms will lead to a longer and tricker building process. 


The granny flat building materials are also important to think about. Your design determines what materials you actually require and your supplier affects how much these materials cost you. Higher-end materials will carry a heavier price tag. People sometimes often opt for these to create a higher-value granny flat. Additionally, better materials could help ensure your granny flat stands the test of time.

Land preparation

A very variable factor that affects granny flat building costs is the preparation for the block of land. This entails tasks such as clearing away trees and rocks that are obstructive towards the building process. These costs depend largely on your particular block of land. You can circumvent these costs if there are fewer obstacles present on your block. Accessibility to the build site lies in a similar vein. If the block of land is harder for builders to get to, it can stretch out the build time and bump up the cost.

Granny flat council costs

Council costs typically refer to the fees and permits necessary to build your granny flat. Submitting applications for these carries a certain cost. They are important to include in your budgeting, as they can add up to a surprising amount. Granny flat council costs are mainly divided between planning permission and building permission. The specifics vary by council, so make sure your information relates to your local shire.

Planning permission involves submitting your proposed blueprint for a granny flat to the local council. It must abide by the relevant restrictions and regulations in your area or you must pay to resubmit it. Planning restrictions encompass features such as the size allotment and aesthetic features of your granny flat. They can often be influenced by your particular location and what your surroundings are. Often, separate approvals are required for features like landscaping and decking.

Building permissions are more focused on the building process. They exist to enforce rules around healthy, safety, sustainability and suitable occupancy conditions in the granny flat. Your chosen builder will be familiar with the necessary building permissions and often submit them for you.

bedroom with hardwood floor, white bed, ceiling fan, blue curtains and wooden blinds

Granny flat servicing and installation costs

Servicing and installation are two important factors contributing to the overall cost of building your granny flat. These are often overlooked but important to be aware of for the overall financial picture. They are particularly important if you have plans to rent out your granny flat. New sub-meters will be necessary to allow the granny flat to have its own independent supply of electricity. This will involve paying a licensed electrician to take care of the installation process. You will also need to do the same for water and gas, and enlist a plumber to handle installation for these.

Learning about all the options you have available to you is important, so contact utility providers to get an idea. There are more sustainable options for services like solar panels that you can make use of in order to save on power costs and composting toilets that can be good if your property is hard to connect to a septic tank or sewage. 

Other granny flat building costs

Along with the existing costs, granny flats have additional costs to be aware of. These depend partly on your intentions for the granny flat. If you plan to rent out your granny flat, you will need to buy the appropriate furnishings and amenities. Kitchen, window and floor coverings are some of the essential additions. And while fully furnishing a granny flat is not  essential, it does help if you’re planning to rent it out. So consider buying furniture like couches and chairs to make your rental more appealing. But granny flats are not always the most spacious, so be sure to get furniture that makes use of the space effectively.

If you’re planning to find other uses for your granny flat, you need to add features bespoke to this. When you use a granny flat as a hobby room, you need to add features appropriate to the hobby. For example, if it’s going to be a gym then you need to buy exercise equipment. Alternatively, you might choose to use your granny flat as an office pod. This could include furniture like a desk and soundproofing in the walls. 

One consideration that is important regardless of your purpose is insulation. This ensures that occupants can be comfortable inside your granny flat, regardless of the weather. Properly insulating the ceilings, walls and floors will also let you save on power bills. 

Tax with granny flats is also important to familiarise yourself with. Whilst granny flats can definitely add property value, they are no longer considered investment properties. So when selling the home that the granny flat is attached to, you will no longer attract capital gains tax. 

Who can help me with my granny flat costs?

All of this might seem a bit overwhelming. Knowing exactly what to budget for, who to contact and how to do it is a fair bit of information to keep track of. If you put in the necessary time, effort and research then you can definitely be successful in making your granny flat dreams a reality. However, if you don’t want all of the stress and hassle of managing every step of the process then look no further. Granny Flats WA have a proven track record of building excellent granny flats and taking the difficulty out of building for our clients. Contact us today and let us help you!