Why a roof changes everything
The WA Building Regulations define a pergola as "an open structure that does not have a roof", though it may have a covering of open-weave, permeable material such as shade cloth. Add solid sheeting and, legally, it's no longer a pergola. It becomes a patio (or verandah, if it's attached to the house), and different rules apply.
Building permit: before and after
| Open pergola | With a solid roof (patio) | |
|---|---|---|
| Exempt from a building permit if | Built with a house, 20 m² or less, 2.4 m high or less, and not in wind region C or D | Freestanding, 10 m² or less, 2.4 m high or less |
| Attached to the house | Exempt within the limits above | Permit needed, any size |
So a 4 m x 4 m (16 m²) open pergola off the back of the house is usually exempt. Put a solid roof on it and it needs a building permit, because it's both attached and over 10 m².
Which "roofs" count
| Covering | Treated as |
|---|---|
| Shade cloth or other permeable fabric | Still a pergola |
| Vinyl or other waterproof shade sail | A verandah (roofed) |
| Polycarbonate, metal sheeting, insulated panels | A roof: now a patio or verandah |
| Opening louvre roof | Not clearly covered by the definition. Because it can close watertight, ask your council before treating it as exempt |
The planning side
The R-Codes treat an unroofed pergola more leniently than a roofed patio. A patio is "an unenclosed structure covered in a water impermeable material", and it counts towards things like setbacks and, on some lots, open space. A pergola that sat happily near the fence may be too close once it's roofed. The City of Wanneroo, for example, asks patios to be 1 m from the boundary, or allows posts on the boundary only if the patio is no longer than 10 m and no higher than 2.7 m, with the roof 500 mm back.
The structure itself
A roof adds weight and, more importantly, wind uplift. Posts, beams and footings sized for an open pergola often aren't enough for a roof. The building permit application needs engineering for the roofed structure, so expect upgraded footings or tie-downs.
Already added a roof without a permit?
It can be approved afterwards with a building approval certificate. A registered building surveyor inspects it, and the council fee is 0.38% of the value, at least $121.