Knowledge base
Does decking change how pergola height is measured?
Why the raised platform and finished overall height must be checked together in England.
Yes, a raised deck can change the finished level from which a pergola is experienced and can create its own planning issue. In England, check both the overall pergola dimensions and the rule for raised platforms rather than treating the deck as invisible.
Planning Portal's outbuilding guidance says the permitted development class does not allow verandas, balconies or raised platforms, with a platform needing to stay at or below the stated 0.3 metre threshold. Its pergola FAQ repeats that a platform must not exceed 0.3 metre. A sloping garden can make the height above ground different around the structure, so show existing and proposed levels on the drawing.
Do not subtract the deck thickness from the manufacturer's pergola height. The installation drawing normally gives the structure's own finished dimension from its mounting surface. Planning assessment uses the actual proposal on the site, including the platform beneath it. Ask the council how it wants levels measured where ground falls away or has previously been altered.
Decking also changes the fixing question. Deck boards are a walking surface, not automatically the structural base required for pergola footplates. A manufacturer may require reinforced joists or concrete support beneath each leg. Confirm the exact model's loading and fixing detail before deciding the post positions.
Rules differ outside England. GOV.WALES has its own platform wording, and Scotland and Northern Ireland use their own planning systems.
Sources
- Planning Portal: pergola FAQ — accessed 14 November 2026.
- Planning Portal: outbuildings — accessed 14 November 2026.
- Harbour Lifestyle: assembly and installation guides — accessed 14 November 2026.
Read putting a pergola on decking, pergola height and headroom and raised platform in the glossary.