The legal difference is the roof
| Pergola | Patio | |
|---|---|---|
| Definition | An open structure with no roof, though it can have a covering of open-weave, permeable material (Building Regulations 2012) | An unenclosed structure covered in a water-impermeable material (R-Codes) |
| Typical build | Open beams or slats, shade cloth, climbing plants | Metal, polycarbonate or other solid roof |
| Building permit exemption | Built with a house: 20 m² or less and 2.4 m or lower | Freestanding: 10 m² or less and 2.4 m or lower |
| Attached to the house | Exempt within the limits above | Needs a building permit at any size (for example at Wanneroo) |
| Counts as a "building" in the R-Codes | No, pergolas are excluded | Yes |
Why it matters
Calling something a pergola doesn't make it one. What counts is whether the top lets water through. Add a solid roof to a pergola and, legally, it's now a patio. That brings the smaller 10 m² exemption limit and, if it's attached, the need for a building permit. See putting a roof on a pergola.
Shade sails follow the same idea. The Town of Victoria Park, for example, treats an impermeable (vinyl) shade sail as a verandah and a permeable one as a pergola.
Planning rules
The R-Codes' definition of a "building" leaves pergolas out, but includes patios. Patios have to meet setbacks; at Wanneroo, for example, 1 m from the side boundary to the post for a patio up to 14 m long. Check your council's rules for pergolas too, especially near boundaries or in the front yard.
Louvre roofs
Opening louvre roofs sit between the two. They're watertight when closed, so ask your council how it classifies yours before you build.