Clear polycarb for roof, what thickness is necessary?

Esho · 09-10-2023 9:42am #1

Hi,

Finally finishing the frame for 3.5 x 3m cover for outside the back door. Very happy with it, got great advice from here.

My wife wants it as clear as possible.

I haven't seen anything except polycarbonate that would fit the bill.

How thick would it need to be?

I have a tin of Tec 7 roofing mastic for the sides to the walls, and will use clear silicone for the gaps in between. And those washered screws to pin them.

Lumen · 09-10-2023 6:31pm

What profile? Solid? Twinwall? Triple? Structured?

What unsupported span?

Esho · 10-10-2023 9:20am

Thanks Lumin It is wood, 600 between each joist and 900 between each purlin.

Sorry shouldve said it is just covering the roof as there is wall on 3 sides

I'm thinking that 2 mm would do it, same as the corrugated I've used before.

The main thing is that it is as see thru as possible

Lumen · 10-10-2023 9:23am

I'd say 2mm solid is too thin. The corrugations in the stuff you've used before made it stiff in the long direction, you won't have that in flat sheet

I've seen recommendations for 6mm+ for roof glazing in solid polycarbonate.

You might ask the supplier, or visit if you can, they know the product. The crowd I used in Dublin had a big skip full of offcuts I could dip into for ideas.

Esho · 10-10-2023 3:15pm

https://www.boards.ie/discussion/comment/121217124#Comment_121217124

Thanks for that. Good one - I 'll go up and look see if I can look at a sample. Im now thinking perspex, as it doesn't discolour.

Lumen · 10-10-2023 3:23pm

https://www.boards.ie/discussion/comment/121218806#Comment_121218806

You can get UV-proof polycarbonate. I think I got it into my head that acrylic was weak crap but I realise now that was because I had it on a shed window that got broken into (which I replaced with polycarbonate). For a canopy sheet you're not looking for burglar proofing so maybe acrylic is better.

I suppose from a strength perspective you might consider whether there are any opening windows above the canopy that would require the canopy to be used as a means of escape (or, say, if a child jumps onto it). If that was the case you'd want polycarbonate as acrylic will snap.

Esho · 11-10-2023 9:30am

Great thanks Lumen - good to know. I'll go for the UV polycarbonate in that case

Shoog · 11-10-2023 9:37am

Had twin wall polycarbonate up for over a decade and it looks as good as new. Span is about 2m front to back with one cross support half way, distance between rafters is about 1m. Would derfinately recommend twin or triple, triple will be a little more insulating.

Lumen · 11-10-2023 9:41am

https://www.boards.ie/discussion/comment/121222349#Comment_121222349

Yeah, but that doesn't meet the requirement "My wife wants it as clear as possible".

I've also seen loads of shocking looking multiwall polycarbonate roofs where (presumably) the detailing wasn't done correctly and algae grew inside, but it's good to know it can be done properly.

Calahonda52 · 11-10-2023 9:51am

https://www.boards.ie/discussion/comment/121217114#Comment_121217114

You are in good hands here with Lumen, he will keep me on the reservation if I wander off😂..

I am puzzled with the 900 between purlins: can you post a picture or two please as you need to support the sheets where they lie side by side on the roof.

Clear silicone wont last when exposed to the sun on a roof that will expand and contract every day

You might be better off using something like this and screw it down through the top

I would go with triple polycarbonate, in truth what ever you put up will meet some "consumer resistance" in relation to light transmittance!

Remember you will need to tape the ends with the correct tape so as they don't fill with crap

The UV resistance stuff will prolly come with two different coloured protective plastic cover to show which one faces up.

I had some cowboys do a job many years ago where they stripped the protective covering off before they cut them

When I came home from work I asked how do you know which side should be up now?

It was a Doh moment.

They replaced them all at their cost, leaving the covering in place for me to review.

Esho · 11-10-2023 2:27pm

Thanks folks

This is the area I'm covering over. No walls needed. It's 3900 across and 3300 the other way.

Lumen · 11-10-2023 4:37pm

I'm no expert on fire safety, but you might be able to get around the means of escape requirement because both of those windows egress to tiled roofs.

At least you're not going to get little Jimmy launching himself out of a window on to the roof whilst reenacting scenes from Batman Ninja.

Calahonda52 · 12-10-2023 7:28am

https://www.boards.ie/discussion/comment/121224487#Comment_121224487

Indeed, but do the windows even meet the fire reg spec, top openings only?

OP so its 3.9 across: what size are pieces spanning the 3.9?

You mentioned

It is wood, 600 between each joist and 900 between each purlin.

so whats what in the picture?

You also need to think about noggins.

IMO, you will need to support that well @ mid span if you are up in it

Shoog · 12-10-2023 7:39am

Double wall poly carbonate can be walked on if it is adequately supported. It's incredibly strong stuff.

One of those glazing bar systems is the only way to deal with the side by side joins as the panels expand and contract with heat by a significant amount. You will also need special washered bolts/screws at the leading front edge to secure down. The hole you drill is bigger than the screw to allow for movement and the cup washer distributes the load. Without them the panels will flex and lift off in a wind.

I would also think about a flashing at the top edge.

Esho · 12-10-2023 9:22am

https://www.boards.ie/discussion/comment/121226725#Comment_121226725

I haven't put in the rest of the spans or purlins yet, but they are the distances I'm thinking of.

There's a crowd in Ashbourne that'll cut UV polycarbonate to fit. After what Lumen said I'll better go for 4mm. I haven't decided how to get it cut yet though.

Def on the support when I'm up there!