Insulation advice or consultant recommendation anyone?!

[Blinkingblimey]

Hi all, We have a top floor flat in a mansard roof (conversion done early 80s) that we’d like to try and insulate....but are really struggling on what (if any!!) our options are.....we had one company come and recommend spraying open cell foam into the void saying it didn’t need a ventilation gap because the foam is ‘breathable’...? I’m not so sure this is the case. There is not the head height to lower the ceiling. Can anyone offer advice?!! Or even better know an honest(!) insulation expert who could run through all the options with us.... does any know of any such person that they would recommend in the London area? Thanks in advance🤞

please don't have foam sprayed on the inside of your roof.

It holds damp, encourages rot, and glues the materials together so that faulty tiles can't readily be removed and replaced with new.

Many roofers refuse to repair a foam-sprayed roof unless it is completely stripped off and all the foam removed.

Goggle "foam sprayed roof" and read all the comments that were not put in by roof-spraying contractors. If you can get a personal recommendation for a local roofer, ask what they think about foam-spraying.

Thank you PigletJohn - understood!! Do you have any recommendation for an alternative?...I know we can get special pastes/paints but was hoping for something that would make a bit more of a difference!

insulated lofts today usually have insulating foam slabs placed tightly between the sloping timbers, then additional, thinner slabs nailed to the face of them, with plasterboard nailed or factory-bonded to those slabs. The ones on the face of the timbers are usually thinner than the ones between them. In an older house the timbers might be four to six inches deep, which is quite good.

Mineral wool quilt can be used, but needs to be about twice the thickness of foam for the same insulating performance.

It is usually done from insidewhile the loft is being plasterboarded during conversion. It can be done from above when the roof has been stripped for retiling. Good felt or membrane under the tiles is needed to prevent damp penetration, and air gaps will probably be needed.

I think there are drawings of the installation on the Kingspan or Knauf websites. They make similar products. If you are in Scotland the method will be different because sarking boards are usual.

Thank you - our worst case scenario is having to strip the ceiling out & see what can be fitted in! Was hoping to find something less messy/invasive!

You can get a bonded foam/plasterboard that you could skin over your existing walls and ceilings, but as they are not very thick, they will not give much extra insulation.

I don't know what the new-build insulation standards were in the1980's. I would have thought more than 100mm of mineral wool, possibly 150mm (it is 250mm now)

Even 100mm is good, provided there are no gaps or draughts.