If you’re thinking about adding a secondary home or granny flat to your property, then congratulations! But first you should know about the hidden costs of building some won’t tell you about.
Australian families are moving to build granny flats on their properties in droves as land prices skyrocket.
However, most people aren’t aware of the sneaky expenses that some builders fail to mention. In addition, the building cost of one home can vary significantly to the cost of another simply due to location.
We’ve compiled a list of the most common hidden costs so you can make a more informed decision when it comes to building. Keep in mind these figures are estimates, and will vary on your property and location.
If you want to know your exact property requirements, talk to our team about ordering a Site Investigation Report.
Most new builds require a Site Survey. This will be one of the first things your designer/builder will organise as one of your costs.
A site surveyor will accurately plot the boundaries and levels/contours of your property, site any trees, easements and existing buildings on your property. It’s all crucial information that informs the design and best place to locate your new home.
Every local Council can have different rules on setbacks, which are the minimum or maximum distances your new home can be to other structures/boundaries. This should be one of the first things you discuss with your designer.
In our experience, a Partial Site Survey costs around $1,500, while a Full Site Survey costs around $2,000.
Check out founder Mel Miller discussing all of these hidden costs of building here, or keep reading below:
Soil Test, Engineering & Wind Rating
Each property has different types of soil, as well as wind ratings depending on their location. These affect how the footings of your home need to be built, how deep they need to be, and the necessary strength/bracing of the materials.
You always need a Soil Test (or site classification report), as well as Footings Design and Wind Rating when building a new home. Your designer or builder should organise these, with the work to be completed by a geotechnical engineer.
In addition, if you’re building with a timber frame you are going to need a set of Structural Engineering drawings. A structural engineer can take care of this for you, and will be able to do your Footings Design as well.
A Soil Test generally costs around $600. While a full set of Structural & Footing Engineering will come in around $1,000-5,000, depending on the size and scope of your design.
Flat vs Sloping Land
When it comes to building on a flat block compared to a slope you’ll likely see a significant cost difference.
It’s due to the additional consulting work and building costs required to ensure your home stands the test of time.
Firstly, Councils and building certifiers normally require a geotechnical engineer to complete a Slope Risk Assessment to test the soil, calculate the stability of the slope and assess the risk. This in turn informs the required footings and bracing.
The report generally costs around $2,500-3,000.
Secondly, we’re finding that building on a slope could add around $20,000-50,000 to the cost of building a small home or granny flat. Yes, you read that right!
This additional cost is due to the extra lengths of steel posts and bracing required, scaffold hire, and requirement for balustrading around the deck.
If your block is in a location with a high risk of bushfires, you will need a specialist bushfire consultant to complete a hazard assessment and mitigation plan.
In our experience, the plan costs around $800 and informs what building materials need to be used in construction.
Depending on the outcome of the report, you may need to use non-combustible or special fire-rated building materials. This includes non-combustible wall cladding and thicker glass.
We’ve seen extreme cases where the same Funky Little Shack in two different areas have a difference in building cost of $30,000 due to the construction materials required.
This one is for those living in rural zones, not connected to town sewerage, or utilizing an onsite biocycle waste system or similar.
You will require a Wastewater Report & Design from a hydraulic engineer to inform what kind of effluent disposal system you will need for your new home. This report generally costs around $700.
The capacity of a system is dependent on, and calculated from, the number of bedrooms you have in both the existing home and the new home you’re intending to build. The hydraulic engineer will inform you whether the existing septic system can be used, or whether a new or additional tank is required.
From our experience, supply/install cost of a new tank for a small home or granny flat ranges $10,000-$15,000. This again depends on how big your home is, and if the system will take care of the main dwelling as well.
Building Approvals (BA) vs Development Approvals (DA)
All new homes require a Building Approval (BA) to be handled by a private certifier.
The cost ($2,000-$4,000) is typically organised by the builder and is sometimes absorbed within the builders fee. Make sure you check with your builder.
Depending on your local Council requirements, you may or may not require a Development Approval (DA), also sometimes known as an MCU, to add a second home or granny flat to your backyard. Your Council or a private town planner can inform you of the Council restrictions and costs (if any).
We’re happy to assist you. We work with local town planners we can put you in touch with.
The costs and time required for a DA is largely dependent on the local Council and town planner. In our experience, it usually costs around $4,000 (combined Council and town planners fee) and usually takes 2-6 months for approval.
What reading all of this you should hopefully have no surprises throughout the process of designing and building your own new home or granny flat!
Of course, there are a range of less common factors that may add additional hidden costs of building. We suggest finding out everything you’ll need at the start of your journey.
Ask us about ordering a Site Investigation Report – this will tell you everything about building on your property, and the feasibility of your project.
We believe it’s crucial to find the right people to help you through the process, and make sure all of the costs are as transparent as possible.
If you’d like further information on anything covered here, please contact us. We have extensive experience in these areas and can put you in touch with licensed experts.