Rockwool insulation

[Speedy Builder5Participant @speedybuilder5]

I can't find any answer to my query on the net. Thinking of installing rock wool insulation in the loft of our 150 year old converted barn.

There is an existing multi layer Al foil / expanded plastic roof lining which is meant to be equivalent to 240mm of glass fiber, but this is not adequate and in practice does not live up to its expectation.

I am proposing installing 100mm rock wool fibre backed with craft paper attached which acts as the vapour barrier between the roof rafters. Rockwool passes fire tests etc BUT the craft paper burns like a torch – how can that be classed as fire resistant ?

Bob

[Speedy Builder5Participant @speedybuilder5]

[Gordon TarlingParticipant @gordontarling37126]

AFAIK, the craft paper layer is not the vapour barrier and is meant to be installed with that side away from the ceiling/plasterboard.

G.

[john halfpennyParticipant @johnhalfpenny52803]

You have a 'warm' roof design (multi- layer insulation immediately under the tiles), so an additional vapour barrier ought not to be necessary. Possibly you already have foil backed plasterboard on the ceiling. If the roof space is sucking up heat, perhaps you have draughts around the roof edge keeping the roof space cold. I have the same kind of roof insulation and it works well at keeping the loft space (and main living area) tolerably warm and usable.

[Dave HalfordParticipant @davehalford22513]

Craft paper is not a vapour barrier either. There are other Rockwool products, one for ground floors has tissue on one face.

[noel shelleyParticipant @noelshelley55608]

As John has said, I think I would be looking for WHY the insulation you have is not working well, it should, but drafts will soon spoil things. Good Luck Noel.

[Speedy Builder5Participant @speedybuilder5]

The multi layer insulation is now not favoured by several of the roofers around here, with temperatures of 40+ deg C in summer and -18 C in winter its not quite the same as the UK. Also, looking on the Rockwool site, the paper backing IS the vapour barrier and should be installed facing the installer.

My original question was "the craft paper burns like a torch – how can that be classed as fire resistant ?" One of the intended uses of the product is for loft insulation where there would be no "Fire protection" from a 12mm plaster board lining. Just seems a little strange to me – perhaps like lining the outside of high rise buildings with certain products.

Bob

[BazyleParticipant @bazyle]

The paper will have been treated with chemicals that reduce its flamability. By putting it at the bottom it is also encased between the rockwool and plaster so by the time it gets near a flame the wood laths and beams will be well away.
As for vapour barrier phooey total advertising bullshit. Firstly you don't want a vapour barrier at that point as the moisture is supposed to go through the insulation and evaporate off the top – otherwise your bedroom will be damp. Secondly as the insulation and its paper is in strips down between the joists the vapour just goes round the edge. For a vapour barrier to work it has to be really airtight, to the point that if say using plastic sheet on the inside of your shed (the more normal query on here) you absolutely have to tape over any joints or it becomes ineffective. Moisture problems due to vapour are not like a quick leak in a rainstorm, they are effects that build up over years so the smallest hole can be a problem.

As to foil insulation – well it gets tested in very controlled and hence artificial conditions which are nothing like real life so it meets building regulations and is a effective s the proverbial chocolate teapot.

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