How to install polycarbonate roof sheets

First things first make sure you have all the correct safety equipment , if working high up its 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.


How to work out how much twin wall polycarbonate roofing you need

Twin Wall polycarbonate sheets have a very unique flat appearance giving the simplest of structures an expensive finish and clean look. Keep in mind that if you want to use twin wall polycarbonate that you will need to consider the design of your structure first. If you’re building your pergola from scratch, you have the advantage of  spacing your rafters to suit the width of the sheets so that you can’t see any joins in the roofline. The standard width of Sunlite sheets is 980mm wide.

If you’re in the process of designing or having your pergola designed, its advised that you speak to the builder or designer about your intentions to use Sunlite sheets, and ask to have your rafters set at 1000mm centres or less. If you’re re roofing your existing pergola the same logic applies. In most re roofing cases however, you’re going to need to roll up your sleeves and make a few adjustments by way of adding & spacing your rafters to accommodate the sheets.

To work out how many sheets you need is pretty simple. As we mentioned, your rafter spacing needs to be 1000mm centres or less. So if you count the spaces between the rafters on your plans you will be left with the correct number of sheets required.

The sheets are sold at 500mm increments in length. To determine the length you need use the same method covered in our polycarbonate roofing guide. Similar to standard polycarbonate sheets you should allow 50mm extra to fall into your gutter.

Sunlite Sheets are held in place by ‘H’ Bar joiners. There are two types 2 piece & 1 piece.

Both types do the same job, the only difference is the ‘2 piece’ allows you to put the base piece down first, applying the Captive wedge rubbers, then laying the cover joiner over, which clicks into place sandwiching the sheet between, making the installation a little easier if access is a problem.

Then there is also the one piece H bar, which operates on the same concept, this type only allows you to ‘slot’ the sheets in from the side, starting from one end. Before doing this you’ll need to frame the sheet in a rubber gasket , creating a watertight seal to prevent leaks.

Other accessories you will need are end caps, to finish off the top bottom and ends of the sheets. These also require rubber gaskets and end cap locks to hold them in place.

To calculate the fixings you will need you need to use the dimensions of your sheets as a guide. You will need end caps and end cap locks for the length of your structure as well as it’s width (you essentially frame the roof in end caps) you will also need h bar joiners for each join between sheets (should mirror the total length of rafters on your structure (less the end rafters)) You will also need rubber gaskets and stoppers for all edges of all sheets.