Adding an extension or extra bedroom will increase the amount of wastewater your property needs to manage.

 

On an unsewered property, it's very likely the existing wastewater system was designed for the size of the original house only. Before finalising plans, it is important to check whether the treatment system and effluent disposal area can support the proposed development.

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Why does an extra bedroom matter?

Wastewater systems are generally assessed based on the potential occupancy of a home (i.e. the number of bedrooms), and not the number of people currently living there.

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An additional bedroom can increase the calculated daily wastewater load. This means the system must be able to treat more wastewater and safely apply the treated effluent within the property.

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What needs to be checked?

Treatment-system capacity

The existing tank, aerated wastewater treatment system or other treatment unit must be large enough for the proposed design load. There's a chance older systems may have been designed for a smaller dwelling or may no longer be in suitable condition.

 

Effluent disposal area

The treatment unit is only one part of the system. Treated wastewater still needs to be safely applied to the land through trenches, beds, irrigation or another approved method.

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The required area depends on factors such as:

• wastewater volume

• soil type and depth

• slope and drainage

• treatment level

• setbacks from buildings, boundaries and waterways.

 

On constrained properties, the available disposal area is often the main issue. Installing a larger tank will not solve the problem if there is insufficient suitable land.

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Proposed building location

An extension, driveway, pool, deck or retaining wall may encroach on the existing disposal area, system components, required setbacks or land reserved for future replacement.

This is why wastewater planning is best completed before the building layout is locked in.

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​​​​​Will the whole system need replacing?

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Wherever practical, we will look to retain, improve and build on the existing wastewater system if it requires expansion to get your extension approved. This is often the most sustainable, efficient and cost-effective outcome for our clients.

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Depending on the site, the solution may involve:

• confirming the existing system has adequate capacity

• extending or upgrading the disposal area

• upgrading pumps or irrigation components

• repairing or servicing the treatment unit

• increasing treatment capacity

• installing a new wastewater system where required.

Our consultative approach means we listen to the client’s priorities and work together to identify the most practical solution for the property, the proposed development and the available budget.

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When should the system be reassessed?

It is worth seeking advice when a proposal includes:

• an extra bedroom or potential sleeping room

• a substantial extension

• a second dwelling or self-contained area

• conversion of a garage, shed or studio

• changes affecting the existing disposal area

• an old, failing or undocumented system.

 

Checking the wastewater system early can reduce the risk of redesigns, delays or requests for more information from council.

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Southern Wastewater Consulting prepares practical, council-ready wastewater assessments for extensions, additional bedrooms and residential upgrades.

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Contact Southern Wastewater Consulting on 0435 575 403 or info@southernwastewater.com.au to discuss your project.