A recent question from one of our customers:
Am investigating a polycarbonate twin wall roof option.
Polycarbonate 8mm twin wall (grey) 610mm wide X 2400mm long X 14 pieces
Joiner 2400mm X 13 pieces
Outside end flashing 2400mm X 2
Inside end flashing 2400mm X 2 this butts onto a plywood wall
I was going to provide a support under each joiner, therefore the only fasteners would run through the joiner, is that how it works?
Thanks for your enquiry.
This is for the 8mm grey at 610mm wide. They are easy to trim to size with a sharp knife or hand saw. We can usually get them trimmed at factory, but unfortunately this isn’t an option for our South Island orders.
You’re correct about the joiner. If that’s sitting on a rafter, then you can put a screw through the bottom plate of the joiner, every 400mm or so. You won’t require a fastener through the Twinwall sheet itself (since it’s only spanning 610mm) as that will be held down by the joiner, once you snap the top plate into place.
I’ve also included the aluminium F channel. This can be used flange facing down on your outside edge. You can fasten the flange through the barge capping on the outside edge, to hold that edge down.
You can then use another F channel on your inside edge. You’d put this one flange facing up the plywood wall, so it would work like an apron flashing. You can also fasten the flange through the plywood, or simply glue it if you don’t want to pierce the cladding.
Lastly, I’ve put some sealer and dust tape in (sealer tape goes at the top edge, dust tape at the bottom edge). The U end cap fits over both tapes to protect it and hold it in place (including under the ridge capping).
I’ve included a 6m ridge capping, the one I think would be most suitable.
Another recent question:
Looking at using Twinwall 610 x 4000 x 8mm sheets, joined using H snap joiners. Can you please confirm the rafter centres measurement between sheets? I’m getting 640mm to allow for thermal expansion (610 + 15 +15).
Also, can i use the off cuts from the 5.8m H snaps and combine them on another sheet (as losing 1.8m per 4.0m sheet)?
Thanks for your email. 640mm is correct.
So if the sheet goes flush to the edge of the first rafter, it will need to be 625mm from the outer edge of that rafter to the middle of the next rafter. Then each subsequent rafter can be 640mm from the centre of that rafter.
Depending on how square the structure is, you may want to make it 10-20mm narrower (or more). Sometimes you may need to make it slightly out of square in order to accommodate existing house/walls etc. Especially over 4m.
It’s much easier to trim the sheets down a bit (with a sharp knife or handsaw) than it is to be slightly too narrow in some places!
But if you’re confident it’ll be completely square and won’t need to trim the sheets then 640mm is right.
You can also use the H snap joiner off-cuts. If you cut them dead square then they but together fairly well. You can use a bit of sealant (suitable for polycarbonate) if you like. But otherwise, even if a very small amount of water gets in through the join it’ll just run down the inside of the joiner channel and out the end.