The main sewer lines (not to be confused with private lines connecting to your property) are Sydney Water assets. Therefore when building near or over their assets we need to abide by their rules and regulations.

In the Central Coast, Gosford/Wyong, the sewer system is owned by council and therefore it is council’s rules that must be followed.

The sewer service diagram needs to be obtained from the sewer system owner to determine if and where there are any sewer pipes on your property.

Our granny flat specialists can do this for you if you don’t have one already.

Zone of Influence

The zone of influence is the area above and beside an asset where loads will have an impact on the sewer asset.

The gradient of the zone of influence begins 600mm horizontal from bottom of the sewer line and extends upwards to the ground surface at an angle of 45 degrees or 25 degrees depending on the soil classification.

Figure 1.1 and 1.2 shows how the zone of influence is arrived.
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When building within the zone of influence (but adjacent to the pipe) you will need to:
  • Requesting a Peg-Out from Sydney Water. There are additional fees for this.
  • Requesting a structural engineer to design a slab in accordance with Sydney Water requirements which typically involves building deeper piers and a broader slab over the section within the zone of influence. (this is shown below in figures 2.1. This will add to the standard cost of a slab.
When building over the sewer line you will need to:
  • Requesting a Peg-Out from Sydney Water. There are additional fees for this.
  • Requesting a structural engineer to design a slab in accordance with Sydney Water requirements which typically involves building deeper piers and a broader slab over the section within the zone of influence as well as encasing the entire sewer line length that is built over plus 0.5m past the building line from both ends. (this is shown below in figures 2.2. This will add to the standard cost of a slab.

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Manholes

If building within 2m of the centre of a manhole cover Sydney Water will need to be engaged for their approval. A structural engineer will need to show how a revised slab design will comply with the below diagram.

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Continue onto the next section of the starters’ guide, Section 94 fees.