Why sewers matter for sheds
Many Perth blocks have a Water Corporation sewer pipe running through the back or side yard, often along the rear fence. That's exactly where people like to put a shed. Building on top of or right next to the pipe can damage it, and stops crews getting to it for repairs. If they need to dig it up later, your shed may be in the way.
Water Corporation's own guidelines cover sheds, so this is a real check, not a technicality.
Step 1: Find out if there's a pipe
- Get free plans from Before You Dig Australia (online, or call 1100). They show the approximate location of water, sewer and drainage pipes.
- Check your certificate of title for a registered easement. That's a strip of land the Water Corporation has a legal right to access.
- Before heavy digging, confirm the exact spot by hand (potholing with a shovel).
Step 2: Work out how deep it is
Find the nearest manhole (access chamber) on the plans. Its lid level minus the pipe level (the "invert") gives the depth. For example, 11.99 minus 10.14 means the pipe is about 1.85 m deep.
Step 3: Check the clearance
Water Corporation's guide for designers sets minimum gaps between a building and a sewer of 225 mm or smaller. A summary:
| Sewer depth | With piles (any pipe) | No piles, PVC pipe | No piles, other pipe |
|---|---|---|---|
| 1.0 to 2.0 m | 600 mm | 1.5 m | 1.5 to 2.5 m |
| 2.1 to 3.0 m | 600 mm | 1.5 m | 2.5 m |
| 3.1 to 4.0 m | 1.0 m | 1.5 to 2.5 m | 2.5 m |
| 4.1 to 5.0 m | 1.0 m | 2.5 m | 2.5 m |
| 5.1 m or more | 1.5 m | 2.5 m or more | 2.5 m or more |
The pipe size and material are written on the plans, for example "150P" means a 150 mm PVC pipe.
Too close? Your options
- Move or redesign the shed. Water Corporation says this is the preferred option.
- Use piles. Footings that go at least 300 mm below the pipe's "zone of influence" (or down to solid rock) let you build closer. A structural engineer must design them, and the pile detail and site plan must be dated and signed by the engineer.
- Relocate the pipe. Possible in some cases, usually at your cost.
Generally, you can build up to or even over an easement if you follow these rules. But it's always worth checking before you buy a shed.
How this fits with your permit
If your shed needs a building permit, your site plan should show easements and pipes. Councils check this. Find out if you need a permit with the shed size checker, and see how close a shed can be to the fence and how to get a shed permit.