Flat roof: Celotex TD3000 ins. boards, Vapour control layer

[l5eeds]

I'm about to fit a new flat roof on me extension as it's started to leak. I'm looking at a warm roof construction with EPDM rubber on top.

To make this a bit simpler for me i've been looking at the Celotex TD3000 series insulation board with ply on the top and a vapour control layer on the bottom. Trouble is I can't get hold of any. The local builder's merchant doesn't stock it, could order some in if they bought 30 boards but as I only want 3, they wouldn't do, understandably. Anyone know anywhere in the Sheffield area which does stock it? Failing that anywhere on the internet?

As it's looking unlikely that i'll be able to get hold of any of this, i'm looking at putting the 3 components in separately:
- Ply
- Insulation
- Vapour Control Layer
First two are easy but without buying a 50m roll, can't seem to find anywhere that will sell vapour control layer cut to size or say 5 linear metres of it. Anyone know anywhere that does?

Any help here would be greatly appreciated!

 

[SurreyRoofingEstimator]

You really need an insulation supplier rather than a general builders merchant, bearing in mind where you are Sheffield Insulation may be your best bet www.siginsulations.co.uk, They are one of the main insulation stockists in the UK and should have stocks of what you require and if not be able to advise of an alternative such as a Kingspan or Powerdeck product.

The VCL you may only get in a large roll (4mx25m) if you use plastic but it should only set you back about £50 for the whole roll. You could try looking for a flat roofing contractor in your area who may sell you an offcut.

 

[noseall]

Regards vcl;

Use foil backed plasterboards. Also use foil tape on any joints to the underside of the deck.

 

[l5eeds]

Thanks for the help guys.

As i've struggled to get hold of this celotex TD3000 stuff think i'm just going to go for standard foil-backed rigid insulation boards and then buy the vapour control layer (VCL) as a sheet and lay between the interior side of the insulation and the roof deck board on top of the joists.

The more I look into VCLs, the more I get confused. From what I understand, it is required to be waterproof (resist water droplets getting through) but allow a certain amount of water vapour through. Right?

I have found some such as Sarnavap 500E and Dupont Tyvek VCL SD2, that fit this but have not managed to find them.
What I have found is breathable membranes such as Dupont Tyvek Supro or Permavent ECO easily available on eBay and other sites cheap enough to buy a whole roll (don't really want to spend no more than about £40). These are designed for pitched roofs to sit between the roof tiles and the insulation. These are waterproof and have very good vapour permeability.

This is surely what the VCL is supposed to do? Will these therefore be okay? or should I find some polyethylene sheet and use that instead? This is cheap enough and is readily available as dust sheets etc. Is this good enough or will this not allow the water vapour to escape? Or is this not a problem? Or what type of plastic should I use?

Another thing, could I just tape all the joints on the foil-backed Kingspan insulation board to provide an effective VCL?

The last thing I want is to do put me roof up and then get condensation forming a few months down the line so really want to do what's right!

As you can imagine, i've heard so many different things about VCLs, i've got information overload(!) so any clarification here would once again be appreciated.

Cheers.