Is my roof design right

[Bonce]

Hello,

After a bit of advice about roof construction particularly in relation to cold roof/warm roof and whether the design we have been given is ok.

So its a lean to roof low pitch, tiles then battens then Klober permo air membrane then 125mm rafters, 25mm gap between top of rafters then 100mm celotex between to the bottom of rafters and then celotex insulation backed plasterboard beneath about 50mm from memory.

Was asking some questions about running cables in the electrics forum and another forum member queried whether the membrane was correct and whether it should be impermeable? The air space isn't going to be ventilated below the membrane and above insulation. BCO has been round but not raised anything but that doesn't mean its all ok.

Advice welcome please and thanks in advance

 

[SurreyRoofingEstimator]

Well, that forum member obvs isn't a roofer, you have design correct and the Klober Air is a top end breather membrane

 

[Bonce]

Thanks S.R.E.,

That sets my mind at rest!!

To be fair to the other forum member he was simply trying to be helpful and didn't say I was wrong. He was just raising a point and he did mention he was not an expert and suggested the roofing forum. He has helped me in a load of other things too in the past so is a top guy in my book.

I got the Klober despite it being rather expensive as reading all the literature regarding membranes etc and condensation problems in warm/cold roofs I was wanting to make sure I could do as much as poss to stop it's likely occurrence.

I am still confused whether its classed as a warm or cold roof - or hybrid? but if the design is sound I am happy.

I have another question if I may. Would it be usual to under the vaulted ceiling before plasterboard etc put a VCL (vapour control layer) in order to try and stop moist air getting up into the roof? If this is the case then I suppose you just joint with tape and around things like lighting points etc you make good as best as can?

 

[SurreyRoofingEstimator]

Most definitely put a VCL between the plasterboard and the internal insulation.

It is a warm roof but is classed as a hybrid as the insulation is not over the rafter

 

[Bonce]

S.R.E.,

Thanks once again very much obliged.

 

[noseall]

It is a cold roof pure and simple as the inso is betwixt and below. It can only be warm if the inso is continuous and above the rafter.

 

[SurreyRoofingEstimator]

It is a cold roof pure and simple as the inso is betwixt and below. It can only be warm if the inso is continuous and above the rafter.

There does seem some confusion on this point, agreed it was always the case that insulation above the rafter denoted as a warm roof but seems to have widened so that it is also a warm roof where the insulation follows the complete line of the rafter and the vapour control layer is below the insulation line stopping any moisture penetrating.