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Multiwall Polycarbonate Guide

Multiwall Polycarbonate are large sheets that are used predominantly in outdoor roofing and canopy projects. They are also popular as screens, either standing vertically or lying horizontally.

What size are these sheets?
let's look at thicknesses first - the sheets are available in 4 thicknesses

  • 4mm thickness, sometimes called Twinwall.
  • 10mm thickness, sometimes called Twinwall.
  • 16mm thickness, sometimes called Triplewall
  • 25mm thickness, sometimes called Fivewall

The sheet is stocked in our warehouse in large sheets measuring 2.1mtr high and 7mtrs in length. We pull these sheets from the racks and cut them on a wall-mounted saw.

Q. Are there different colours available?

Yes, the most popular 'colour' is Clear but you can also get both Opal (White translucent) and Bronze translucent in thicknesses 16mm and 25mm. Only clear is available in 10mm.

Q. What about Cutting these sheets?

As mentioned, Multiwall stock sheets are 2.1mtr in height and 7mtrs in length.

The sheets can be cut to size at no extra charge, to match your roof or canopy project. The most popular use of these sheets is in Lean-To-Roof applications, where the sheets run away from a building/wall with a gentle slope, allowing rainwater to run down the sheets to a collecting gutter. For cutting purposes, we call this slope the 'FALL'.

In the above picture showing the sheet in our warehouse and also the diagram below, you can see that the ribs or flutes in the sheet run Left to Right along the 7mtr length. It is recommended that these flutes be placed running down the direction of the Fall.

mulitwall lean to roof

Hence the maximum width of sheets used in roofing applications will always be 2.1mtr

The maximum length of a sheet down the slope or Fall, technically can be anything up to 7mtrs.

Installed this way, if there was any build-up of water droplets (condensation) inside the internal flutes, then the moisture or droplets could be vented downwards. The ends of the sheet are never left entirely open - as insects or dirt could enter the flutes - instead, a vented breather tape is applied to the sheet ends. This makes the flutes breathable and aids in the venting of any moisture that might gather inside the flutes.

Before we apply the breather tape, we always insert a compressed air nozzle into all the flutes to blow out any cutting swarf that may have lingered when we cut through the sheet. The sheets are then taped and supplied to you. You'll often hear us say that the sheets are "Cut, Blown, and Taped".

Q. Do sheets have to be taped?

If you want to further cut sheets on site, or in situ on your roof e.g. to go around obstacles, we can blow out the sheet and then supply the tape loose, so that you can make your adjustments on site and then apply the tape yourself. Just let us know when you're ordering - either phone us at +353 01 409 8000 or simply add a note with your online order that says 'Supply Loose Tape'. There is no extra charge for the tape to be supplied loose (or applied to your sheets).

Q. What spacing should I allow between rafters?

If you haven't installed any rafters yet, then the ideal scenario is outlined below.

Utilize the max width of the sheet, by spacing rafters at approximately 700mm centers.

Using this spacing, you would have a start rafter, the next intermediate rafter at 700mm distance, and then a 3rd rafter, again 700m from the intermediate rafter.

Spacing rafters this way, you would utilize the full width of the sheet 2100mm (2.1mtrs).

1st rafter: sheet is wedge fitted into F profile and the f profile sis screw fitted into the side of the rafter.

2nd (Intermediate) rafter: The sheet is lying on top of this rafter. The usual fixing method would be to use Fixing buttons, inserted via the top of the sheet from the outside. You are left with small circular speed bumps lying down the fall of the rafter.

3rd rafter: The sheet would share this rafter with the next sheet and a Capex Bar would be used over this join.

Similarly, the ideal scenario for the 'width 'of your roof, would be in 2.1mttr sections, so 2.1mtr, 4.2mtr, 6.3mtr, etc.

By doing this, you are utilizing the full width of the sheet. 

Of course, if this doesn't suit you, then we can cut or trim the sheet to make it suit whatever width you are going for. The manufacturer recommends the 700mm spacing as being optimal but the sheet can be cut to suit your needs as you may have rafters closer together or slightly further apart.

Q. How is the sheet fixed down or secured in place

Visit our Roofing Accessories section to learn more.