warm roof with insulated panels?

somebodude

I'm looking at reroofing an extension flat roof with insulated panels,

these kingspan ones for example https://www.kingspan.com/ie/en/products/insulated-panels/roof-panels/quadcore-ks1000rw-roof-panel/

And also the pitched roof - they seem attractive as a cheap alternative to slates or tiles, but as they'd be fixed to in-place wooden rafters, I'm not at all sure how the damp/condensation is managed.

Those panels are pictured used on agricultural and industrial constructions, but I find nothing about domestic use. Non-insulated Panels are discussed, when used with separated breather membranes and insulation, but the insulated panels (which won't have space for a membrane between the outer layer and the insulation) are not mentioned.

So Q: it is practicable to mitigate damp with these panels? On the one hand, ridge and soffit ventilation would be easy, but then I'd lose a lot of warm damp air, and of course the heat.

Ginger83

https://www.boards.ie/discussion/2058297428/warm-roof-with-insulated-panels

A key element of a warm roof is a vapour barrier. I would ask Kingspan.

somebodude

This is where I get confused.

The kingspan stuff has sealing all around it's edges and joins, so rain won't come through from the top, and won't come through from the bottom either.

The insulation is the PIR type, so moisture-impermeable. The supporting rafters will be in the warm-roof space subject to ambient internal moisture.

Where would the membrane go, and what is it supposed to do?

10-10-20

https://www.boards.ie/discussion/comment/120627474#Comment_120627474

I'm confused now. Are you intending on using the insulated panels on a flat roof laid horizontally or are you intending on making the flat into a pitched roof?

The vapour barrier would normally be fitted tight to the inside face of the insulation so that no damp & warm air can penetrate the voids and condensate at any level. I'd probably suggest that these panels be fitted together and then an additional layer of insulation be fitted in an offset manner to overcome any voids and then a VCL be tight-fitted to the underside of the inner face. That applies even when the insulation or panel has a foil face.

Look up "Steve Roofer" on Youtube and review his mock-up videos where he shows how all of this must be sealed especially where there is a high humidity level within the room below.

Ginger83

Do you know the current build up of your flat roof? Is there a deck on the joists / rafters? If so it may be possible to keep the deck, put the vapour barrier and then the Kingspan.

somebodude

current build up of your flat roof?

ancient bitumen on chipboard, maybe some joists can be kept.

Are you intending on using the insulated panels on a flat roof laid horizontally or are you intending on making the flat into a pitched roof?

Both.

For the pitched roof it works out around the same cost per m2 as slates, but without the 5 thousand nails.

German quick howto: https://baubeaver.de/dampfbremse/ says to use membrane inside of insulation, when using insulated panels in pitched roofs.

I suppose the general answer then is to use the panels like slates and then have a membrane under counterbattens as usual, and inside that again, maybe fibreboard or other breathable partitioning.

10-10-20

https://www.boards.ie/discussion/comment/120631357#Comment_120631357

From what I can work out they are looking at a "hybrid" insulated roof made up of 60mm glasswool under the tile battens, joists surrounded by glasswool (200mm) and inner-side battens with glasswool where the gyp-board is mounted to (20mm?). They then compare that against the same configuration where the VCL is installed between the battens and the studs.

That's fine as it avoids interstitial condensation shown in the first graph by insulating the joists from both sides. In your case you don't have joists (that we know of) within the insulated element, but you do potentially have cold spots where the roofing panels meet. As mentioned above, only Kingspan would be best placed to advise where the VCL should be best installed in a configuration like what you're proposing as that German example doesn't match your configuration exactly.

somebodude

only Kingspan would be best placed to advise where the VCL should be best installed

I downloaded all thier docs, but they had nothing about damp control, and all the pictures were of cattle sheds and warehouses

somebodude

found in the wild