First things first: make sure you have all the correct safety equipment. If working high up it’s best to have a safety harness and a scaffold. Always exercise extreme care when walking on a roof; appropriate footwear is also necessary. Never walk on or apply your weight directly to sheeting.
Polycarb corrugated sheets need a minimum of a 5 degree fall this ensures adequate water runoff. Purlin Spacing for Corrugated sheets is 800mm for end spans and midspans are 1000. Greca sheets require 900mm for end spans and 1200mm for midspans. If installing under a gutter, use back channel with profiled infill strips.
When you start installing the sheets the first thing you need to do is find a sticker showing you which side of the sheet faces the sun. It’s imperative that this is followed as there is only one side of the sheet that’s UV protected. The life of the sheet may be shortened and discolouration may occur if the unprotected side is exposed to the sun.
To start the installation, first lay out the purlin tape over the rafters to prevent expansion noise. Then cut your sheets to size. Sheets can be easily cut with a pair of shears, a fine-toothed handsaw or a circular saw with a cut-off blade suitable for plastic.
Start with the lower sheets first, keeping the openings where the sheets overlap away from prevailing wind. Allow an overhang of 50mm into the gutter. Overlaps will differ between profiles, corrugated sheets have an overlap of 1 1/2 corrugations and greca profile has just one overlap.
Polycarb sheets naturally move with temperature, so you will need the correct fixings to allow this to occur without issues. Polycarbonate screws will pre cut a hole wide enough to allow for this expansion. This prevents the sheets from buckling. The large rubber on the screw will also seal on the sheet and stop any water from penetrating the roof. It’s important your fixings need to go through the crest of the corrugations on your sheet. You should use a (5/16”) Drill hex driver.
The frequency of screws required for corrugated and greca sheets is every 2nd crest for end purlins, every 3rd crest on the mid purlins and on Trimdek sheets use a screw on every crest. If you’re in a high wind area fix corrugated and greca sheets on every second corrugation on each purlin/ batten
It’s best to tighten the fixings enough to prevent rattling. However you need to be aware that over tightening may cause distortion and excessive stress with possible failure in the sheets the result. Please also only use the correct branded fixings as recommended by the manufacturer, as these are designed to be compatible with that brand of Polycarbonate Roofing.
Once you have successfully installed all of your roof sheets you will need to finish off the structure with suitable metalgoods such as a ridge cap and barge caps. These will all fit over the top of your sheets and prevent air and water from penetrating your structure.
If you have any questions about roofing or would like a quote on materials please don’t hesitate to get in touch.
Purchase all your roofing requirements from the Softwoods online roofing store.