25mm Multiwall Polycarbonate

We recommend a maximum sheet width of 900mm for 25mm multiwall without extra support. The manufacturer allows wider spans at light loads, but 900mm is the safe figure for a DIY roof on standard glazing bars. That is a sheet figure, not a structural one, so check your wind and snow exposure, or call the technical team.

25mm is the usual starting point for a conservatory you sit in year round. It loses about a third less heat than 16mm and passes about 62% of daylight in clear. 35mm loses about a sixth less heat again and is the current standard for new roofs. If winter comfort matters more than cost, choose 35mm.

Just the top face. The UV layer is co-extruded into one side of the sheet during manufacture, and the printed protective film marks it. That side must face the sun. Fitted upside down, we have seen sheets yellow and crack within a couple of years. Fitted correctly, the sheet is warranted for ten years against loss of light transmission.

Look for the protective film with printing on it: that is the UV-protected face, and it goes towards the sun. Leave the film on until the sheet is in place, then peel it off. The flutes, the hollow channels inside the sheet, must run down the slope so condensation drains out at the bottom edge, never across the roof.

The largest 25mm sheet is 2100mm wide by 7000mm long. We cut from that stock size to your measurements, to a tolerance of plus or minus 5mm. Cut sheets are bespoke and cannot be returned, so measure your rafter centres and roof length twice. We can pre-tape the cut ends on request, aluminium tape at the top and breather tape at the bottom.