How to assemble a roof, using multiwall polycarbonate sheet
When we cut the polycarbonate sheet, it is imperative that we blow out the sheet, to ensure that there is no sawdust or plastic swarf in the flutes.
Once that is done, we then apply solid tape to the top of the sheet, which is nearest to the wall and apply a vented tape to the other end, which runs near the gutter. This helps to protect the sheet from any water ingress. The vented tape allows for the air in the sheet to expand and escape from the vents in the tape. To protect that, as it is running into the gutter, we have a u profile which clips over the vented tape and protects it from moisture.
In conjunction with that, once the sheets are in position, we apply a capping bar. Capping bars are available in both a white or brown finish. They are pre-drilled and are available in 40mm wide and 60mm wide.
When assembling the roof, we have a rafter gasket, which will be sitting down on a jointing rafter, where we will have 2 sheets coming side by side. We allow for an expansion on the sheet, so as the sheet heats up during the day and cools down at night, the sheet will expand and contract due to the coefficient of linear expansion. It is imperative that you leave a 10mm to 12 mm gap between the 2 sheets. The capping bar comes across the joint and the fixing screws, usually 60mm long, are placed into the pre-drilled holes. It is essential that you don’t over tighten the screws to allow for some expansion and contraction. Finally on the gable end of the sheet, there is an aluminium F profile, which finishes and fixes to the gable end of the sheet.
Fitting Intermediary Rafters
For intermediary rafters, those rafters where sheets are not been butted edge to edge and there is no need for a capping bar to be used, a simple use of a fixing button will cover the job. To use this, pre-drill a hole 18mm in diameter, to allow for the expansion of the sheet. Put a small bead of, neutral curing silicone (please remember it must be neutral curing silicone, as acetoxy silicone may in fact attack the polycarbonate sheet), into the hole. The foam gasket is inserted inside the ring, the lug is then placed into the hole, the screw goes down in place and the whole thing is drilled down into position. Again, do not over tighten the screw, break off the lug, place a small amount of silicone on the screw head and insert the cap.
Water Tight Sealing
When the sheeting is in position and the roofing is almost completed, it is necessary to achieve a water tight seal between the house wall and the multiwall polycarbonate sheet. This is achieved by using a butyl backed lead flashing, which is available in white and lead colour.
It is very easily adhered to the sheet, to the wall and the butyl backing makes it a very easy process, as opposed to having to chase the wall using the standard lead. As an alternative to using the butyl flashing to obtain a pure water tight seal between the sheet and the house wall, you can use the alternative of a complete wall flashing profile. A rafter gasket is placed on the wall plate, the sheet is placed up onto the rafter gasket, the aluminium profile is brought into place, flush with the wall, sitting down onto the sheet and screwed into position. Finally some neutral curing silicone is placed between the wall and the profile and the profile is screwed to the sheet. This will achieve a very professional finish.