A polycarbonate pergola roof is a shading product that buyers often treat as a glazing product. The difference shows up in July, when a clear roof turns a terrace into a hot box and the client blames the sheet.
A garden designer in Provence covered a 4 x 6 m pergola in clear 8 mm twinwall. Surface temperature readings hit 58 C in August and the seating was unusable between noon and four; the replacement was bronze 10 mm solid and the readings fell by 12 C.
Polycarbonate pergola roof sheet selection
- 8 mm twinwall: shade plus insulation, 700 to 900 mm span
- 10 mm solid: clarity and impact, 1200 mm span
- 16 mm multiwall: cold climates, higher insulation
- Tint: bronze or opal to cut glare and heat
Twinwall is the default for shade because the structure breaks up direct sun. Solid sheet is the answer where hail or falling branches are the risk, and where the client wants a clean plane of light rather than a diffused one.
Rafters, edge profiles and water
Rafters carry the sheet and set the span. A 10 mm solid panel at 1200 mm spans comfortably in a domestic pergola; the same panel at 1800 mm needs intermediate support or a thicker sheet.
The edge is where a pergola roof leaks. A U-profile or a matching end cap closes the flutes of twinwall and stops water tracking back along the channels. Left open, the sheet fills with condensation and dirt within a season.
Ventilation is part of the roof design. A gap at the ridge, or open gables, lets hot air escape; a sealed box heats up whatever the tint. On a lean-to pergola, the high side should be open.
Where the pergola connects to a house wall, the flashing detail is the same as for a canopy, covered in polycarbonate canopy sheets, and the carport case is in polycarbonate carport roofing.
Send your pergola plan, span and climate to oversales@rpplexiglass.com for a roof sheet quotation.
Frequently Asked Questions
What polycarbonate for a pergola roof?
8 mm twinwall for shade with insulation, or 10 mm solid for impact resistance and clarity. Bronze and opal tints cut glare; clear sheet turns a pergola into a greenhouse in summer.
How far can polycarbonate span on a pergola?
8 mm twinwall spans about 700 to 900 mm between rafters depending on load; 10 mm solid reaches 1200 mm. Snow load and wind uplift decide the final figure, so the structural calculation comes first.
Does a polycarbonate pergola roof get too hot?
A clear roof does. A bronze or opal tint reduces solar transmission and the surface temperature, and cross ventilation at the ridge is what keeps the space usable. Sealing every gap is the mistake.