Can I fill in a swimming pool and build a Granny Flat?

August 14, 2023

With careful and correct planning you can turn an unwanted pool space into the perfect place for a Granny Flat

Pools undoubtedly offer a refreshing escape during scorching summers, becoming a hub of relaxation and fun. However, their allure comes with responsibilities. Pool maintenance can be demanding, involving regular cleaning, chemical treatments, and equipment upkeep. Moreover, even well-maintained pools have a limited lifespan due to wear and tear. If you find that you're no longer making the most of your pool and the upkeep has become burdensome, repurposing the pool area by having it professionally filled in could open up exciting possibilities. The land once occupied by the pool can be transformed into a valuable space for a secondary dwelling, like a Granny Flat. This approach maximises your property's potential, creating new living space while sidestepping the ongoing costs and maintenance of an underutilised or aging pool.

The importance of correct pool site removal for a Granny Flat

The idea of constructing a granny flat over a swimming pool site might seem intriguing, but it's not as simple as placing a new structure over the existing pool. The first and most crucial step is the complete removal of the swimming pool itself. Whether your pool is made of concrete or fiberglass, it's imperative to clear the area of any remnants of the old pool. Why is this step so vital?

Foundations are the backbone of any building, and they must be built on stable ground to ensure the structural integrity of the entire construction. When you're building a granny flat over a former pool area, the ground needs to be prepared thoroughly. If there are any remnants of the old pool, such as concrete debris or discarded building materials, these can cause instability in the ground, leading to potential issues with your new building's foundation.

Introducing VENM: Virgin Excavated Natural Material

Imagine starting the construction process and realising that your foundation is compromised due to hidden debris from an old pool. Not only would this be a major setback, but it could also lead to significant delays and expenses. Bits of concrete, rusty rebar, and other building materials can cause havoc beneath the surface. Additionally, the presence of asbestos, a hazardous material commonly used in older construction, can pose health risks if disturbed during construction. To avoid these issues, a thorough and professional removal of all debris is paramount.

The process of building over a former swimming pool site involves more than just clearing the area. It requires proper preparation of the ground to ensure stability and safety. After removing all debris, the space needs to be filled with suitable material known as Virgin Excavated Natural Material (VENM). This term holds great significance and is recognised by environmental authorities across different states.

Granny Flat Wollongong -4

Know what services are connected, and safely have disconnected

Is your pool connected to electricity - for example your pool pump, or solar? or is there gas or any other services nearby or connected to the area that will require demolition? Consider the existing services to the pool such as power and gas that may be within the building foot print, and have these safely mapped and disconnected by a qualified expert.

VENM definition:

VENM is defined as virgin excavated natural material (e.g. clay, gravel, sand, soil and rock) that is not mixed with any other waste and that: 

(a) has been excavated from areas that are not contaminated2, as a result of industrial, commercial, mining or agricultural activities, with manufactured chemicals, that does not contain sulphidic ores or soils and does not contain naturally elevated levels of certain elements or compounds, or

(b) consists of excavated natural materials that meet such criteria as may be approved by the Environment Protection Authority (EPA) 3.

The following is not classified as VENM:

  • excavated material which has been stockpiled, reused or processed in any way or has been sourced from a site where contamination is present or has been previously identified.
  • fill material, engineered or manufactured topsoil, material which has been impacted by anthropogenic inclusions (for example asphalt, road base and building rubble) or vegetation waste.

Do you need a complying development certificate (CDC) or development application (DA) to fill in a pool?

A pool is not just a recreational feature; it's also a legislated construct that requires careful adherence to regulations. Whether you're planning to build or remove a swimming pool, obtaining the necessary permissions and approvals from the local council is essential. Furthermore, regardless of whether the pool is filled with water or not, it must be surrounded by a compliant fence until it is filled. Failing to maintain an appropriate pool enclosure can result in fines or, even worse, an accident, so definitely leave the fence.

If you are filling in the pool well before you start your construction venture, you might obtain a CDC. Getting a CDC for filling in a pool is quite easy to do, simply search local certifiers who do this, they will make the required lodgement with council to notify them. Your chosen contractor for filling in the pool will also need to see a copy of the CDC before they can start the works. A client with Cubitt's recently did this in NSW and the cost was circa $500.

If your pool is still in place when you have your initial consultation with Cubitt's, we will do all the council work for you. That is, when lodging a DA for your new structure, we would include the removal of the pool in the DA.

Pool filled in and compacted for stability

Just filling the pool area with VENM isn't sufficient. The material also needs to be properly compacted. Compaction ensures that the ground is stable and won't shift or settle under the weight of the new Granny Flat. A stable foundation is the key to preventing future problems such as structural damage, cracks, and uneven settling.

Once the process of repurposing a pool area for a new structure begins, it's important to anticipate a potential timeline of up to two weeks or more. Keep in mind that work cannot proceed on wet ground to ensure a solid foundation. In the case of a fiberglass pool, the procedure involves stripping the pool bottom first to preserve the shape of the pool, the filling process commences at one end, typically from the bottom, while carefully compacting the fill material as it's added. The attention to detail during this process is vital to create a solid foundation for the forthcoming Dwelling.

TIP: Our client was advised not to drain their fibreglass pool long prior to the excavation - this is because in the event of heavy rain, the waterlogged soil around the pool may cause the fibreglass to pop up, making it far more difficult to remove.

Provide all the detail you can to your builder

When you're considering building a Granny Flat over a swimming pool site, it's crucial to communicate this plan (or that the site formerly had a pool on it) from the very beginning of your building process. Why? Because proper soil testing must be conducted to determine the suitability of the ground for construction. Soil testing evaluates factors such as soil composition, density, and load-bearing capacity.

In all cases, an Engineer will also ask us to extend our footings past the existing base of the pool.Our foundations will be designed by an engineer to account for the changes and disturbances in the ground. All information you can give helps engineers and builders conduct the appropriate testing and design the appropriate foundation for your Granny Flat.

More Expert Building content from the Cubitt's Construction team:


Cubitt's are committed to making your building project stress free and simple. Responsible for your result, you can be assured that we will be aiming to complete your project with the best outcome for your long term use of the home. Building a home is a journey we are privileged to go on with our clients, and Cubitt's are committed to being completely transparent and delivering the highest standards of communication along the way.

We're working towards you enjoying your home for decades to come. We work with expert engineers who help us deliver your building plans to the most up to date local council regulations. At every step of the way we are working with the engineers guidelines to validate expected building conditions. When there are surprises, (which there mostly aren't) you can be assured that your building supervisor has the expert knowledge to guide the decisions you make next - and the team to back it up.


Free On-Site Assessment at Your Property

Interested in finding out how to make a positive investment from a Cubitt's Granny Flat or Home Extension? Get in touch for a no-obligation site inspection today.

If you are looking to purchase a new property and want to do a Granny Flat Suitability Check - please use this form instead.

We require your name, email and phone number to get back to you - and the more you can tell us about your build project, the more effectively our local teams can help.


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About Harry Kim

Harry has worked on building sites since the young age of 16, both on commercial and multi high rise buildings, before moving into residential construction management with Cubitt’s. Harry leads a team of 10 site supervisors, 30 employee trades and a large, fluctuating group of longstanding subcontractors.