The 10 m² rule
WA's Building Regulations list some small structures that don't need a building permit. For sheds, the key test is that the shed is freestanding, has a floor area of 10 m² or less and is no taller than 2.4 m. Miss any one of the three and you need a permit.
| Shed size | Floor area | Building permit? |
|---|---|---|
| 2.3 m x 2.3 m | 5.3 m² | Usually not (if 2.4 m tall or less) |
| 3 m x 3 m | 9 m² | Usually not (if 2.4 m tall or less) |
| 3 m x 3.3 m | 9.9 m² | Usually not (if 2.4 m tall or less) |
| 3 m x 4 m | 12 m² | Yes |
| 6 m x 6 m | 36 m² | Yes |
| Any size, attached to the house | Any | Yes |
How to measure
Floor area is the length times the width of the floor inside the walls. Height is measured from the natural ground level to the highest point of the roof. On a sloping block, the high point is measured from the lowest side, so a shed can be taller than you expect.
"Freestanding" means not touching anything
A shed that shares a wall with the house, the garage or a patio, or whose roof joins another roof, is not freestanding. It needs a building permit at any size.
No permit doesn't mean no rules
Even an exempt shed has to follow the planning rules and be built properly. Things that catch people out:
- Front yard. Sheds in the street setback area usually need planning approval.
- Boundaries. Walls on or near a boundary have height and length limits in the R-Codes.
- Easements and sewers. You generally can't build over a sewer line or easement without permission from the Water Corporation or the easement owner.
- Heritage and special areas. Heritage-listed places and some estates have their own rules.
- Bushfire-prone areas. Sheds close to the house can need extra construction measures.
Bigger sheds on house lots
For bigger sheds, the R-Codes set standard limits for outbuildings on a house lot. In summary: all outbuildings together up to 60 m² or 10% of the lot (whichever is less), walls up to 2.4 m high, a roof ridge up to 4.2 m, and not in the street setback. Councils can vary these in their local planning policies. A shed outside them needs planning approval, and some councils allow larger sheds on bigger lots.