Lounging Lizards | Sewers and Granny Flats in NSW
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Sewers and Granny Flats in NSW

Sewers and Granny Flats in NSW

Can I Build a Granny Flat Over a Sewer?



Beneath the streets, a vast network of pipes, sewers, manholes, and pumps are hard at work throughout the day to keep our lives sanitary and protect the environment, and when building a granny flat on your property, they must be kept in mind. When building a granny flat in Australia, you’ll need approval that it will do no damage to the sewer on your property.


Our granny flat building professionals can handle all of the heavy legwork for you, but just so that you’re in the know, here are the regulations you must consider:


Your Sewer or the City’s?


The first thing that you must find out is whether or not the flat will influence your pipe or the city’s property. The sewer pipe connecting your home to the water main is your private line and personal property, and you are free to build on it as you see fit (though there are some considerations to keep in mind). You can even divert it if you really want a granny flat!


However, the Sydney Waters sewer main is not your property, and you must receive permission to build on or adjacent to it. You may even be forced to reinforce the pipe to make it safe to build on. This adds a bit of extra work, but it’s nothing we can’t handle for you.


You will need to obtain a sewer diagram for your property to determine how to proceed.


Granny Flat Building Options and Requirements


If your property is home to a water main that will be impacted by the development, you are subject to certain regulations. The “zone of influence” is the area above and beside the sewer where the weight of your flat will have an impact on the pipe. When building your flat, this must be taken into account.


Note: A “peg out” or sewer survey is a survey conducted by a certified technician in which they assess the property and decide if there are any special requirements for your sewage system and construction project.



There are several scenarios that can play out:


  • Building Directly Over the Sewer: Building directly over the sewer is the most complex and costly option. If you wish to build on top or within 600mm of the city’s sewer asset, you will need a peg out and a civil engineer to design a concrete encasement for the asset in order to build over it. Sydney water has a complete guide on what you need
  • Building at Least 600mm from the Zone of Influence: If you intend to build at least 600mm from the zone of influence of the pipe, then you will still require a peg out. A civil engineer will then have to design footings which will extend below the zone of influence into the ground in order to reinforce the asset.
  • Building Further Out: If you plan to build at a distance of at least the sewer’s depth + 600mm, then you will only require a peg out and routine sewer inspections. Building at a distance of at least two times the sewer’s depth requires no further approval.


Building a granny flat over a sewer certainly doesn’t make things easier, but it’s nothing we can’t handle. If your new dwelling will exert any pressure on the city’s sewer asset, you must obtain approval and most likely reinforce the structure. A professional granny flat building service should be able to handle everything without issue. Feel free to direct any further questions about getting your very own granny at to Lounging Lizards.

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