Before you start

• Before you get stuck in, you need to be mindful of a few things:
• Building regulations only permit you to put a roof that’s 20 square metres or under onto your pergola, so make sure you measure it up properly and are under the limit.
• You’ll need a minimum of a 5 degree fall, so the rainwater can drain off it.
• It’s always a good idea to check with your council for any updated building regulations, just in case.
• There are a number of different styles and colours of polycarbonate roofing, so just select the type that’s right for you.

• Measure the length your sheets will need to be. This is the distance from the house to the end of the pergola, then allow for a 60mm overhang to allow for guttering. It’s a good idea to measure each sheet individually, just in case your house and pergola beam aren’t exactly parallel.
• Transfer your measurement onto a sheet of polycarbonate roofing using a straight edge and permanent marker.
• Cut the polycarbonate roofing to length with some tin snips or a fine tooth hand saw.
• Follow the same steps for the rest of your sheets of polycarbonate roofing.

Flashing

• If the roof of your house doesn’t have very big eaves, then you’ll need to install some flashing so the water doesn’t leak between the polycarbonate roofing and the side of your house.
• In this situation we’re using an “Apron Flashing”. This tucks up in between the weatherboards, giving a weathertight seal. You can get the Apron Flashing made up to any size you need, just visit your local Mitre 10 store and they’ll sort it out for you.
• Using a pry bar, gently separate the weatherboards so you can create a gap big enough for a sabre saw to fit in – this will allow you to cut the nails holding down the weatherboards, so the flashing will easily slip up between them at least 40mm.

Installing polycarbonate sheets

• Place the first sheet of roofing onto the pergola, sliding it under the flashing. Make sure the roofing is parallel to the rafters, and that there’s a 60mm overhang at the end. Also, ensure that the end of the sheet that’s been cut is against the house.
• Once it’s in place screw the sheet onto the purlins of the pergola.
• Using 14g x 50mm guage polycarbonate fasteners will mean you don’t need to pre-drill any holes, and will drastically cut your installation time down.
• Fix the screws through every second high point on the roofing - this stops water leaking through the holes. Use a straight edge to mark your screw points, so they’re in a neat straight line. Don’t screw in the first high point, allowing for the overlap of the next sheet.
• Drill the screw down just enough so that it doesn’t push the sheet down too far.
• When drilling the holes through the flashing and polycarbonate roofing, use a standard roofing screw.
• Place the next sheet of roofing, ensuring there’s an overlap, and that it’s in line with the previous sheet.
• Drill through the overlap, and continue fixing the sheet as per the steps above.
• Renail your weatherboards, through the flashing, as you work your way along.
• Mould the soft edge of the flashing into the corrugated roofing.
• Continue laying the rest of your sheets. When you get to the end sheet, you may need to cut it to width – if this is the case, make sure the non-cut side is on the outside.