Twin/multi-wall polycarbonate thickness & roof span

[John Stumbles]

It's a while[1] since I've played with twinwall and I want to make an awning-style roof over the patio, to keep the rain off. It'll be about 3m deep (from the house wall to the outer edge) and about 3m5 wide. I'm planning to make a frame of treated CLS-ish timber with spars at suitable centres to take the sheeting. Last time did anything like this I used 6mm twinwall but it was a bit floppy and wimpy-feeling[2]. What's a sensible thickness to go for, for reasonable width of sheets? Any recommendations on fixing systems (glazing bars etc)? And heads-ups (or downs!) on suppliers? Any other gotchas?

tia

[1] measured in decades [2] though it did just about survive a brick falling onto it from about 10' above - the brick made a big dent in the sheet but didn't go through (and I don't recall if it broke either skin)

[John Rumm]

10mm is probably a better minimum... Last time I used some (on a mate's conservatory roof - 7m wide, about 2.5m depth) I went for Corotherm and ordered from:

Fitted glazing bars the length of each rafter, and then selected a width appropriate for the rafter spacing. IIRC there is a requirement to add mid span support when over a certain length.

Fitted ali tape over the top cut edge (which went under the flashing), and then fly screen mesh tape over the bottom edge to let it breathe.

Installation guide here:

The end result was nice and solid and looked pretty good.

[David.WE.Roberts]

Give me a while and I'll post photos and details of our veranda roof.

Recently done, but has been tested by snow.

Cheers

Dave R

[valromano.mail]

Could you please tell me what distance the rafter should be? If I use a 700 mm polycarbonate sheet (and have to allow 2mm each side against the support ing bar that sits on the rafter) should I also take into account the thickn ess of the inner part of the supporting bar, where the screws fox it into p lace?

So my question is, given that the gas hiss are 50mm with an inner part (whe re the screws go) of 15mm should the spacing of the rafter be calculated as follow:

Sheet width 700 mm Space to allow expansion 2. mm Inner part of support bar 7.5mm (15mm/2)

Spacing of rafter 709.5mm?

Thanks

[John Rumm]

Sounds about right...

I most cases the rafter positions are already set, so you just cut the sheet to fit once the glazing bars are fitted.

You probably ought to refer to the installation instructions for your particular roofing system regarding the amount of expansion space to leave. e.g.: