expandingfoam spray on loft conversion

[dave m]

does the expanding foam spray for inside of rafters work?does it insulate? will it adhere to roofing felt as mine is shot....cheers

[KARL]

It certainly will adhere to anything it is sprayed onto and it will insulate. The ideal situation is for the roof to be fully lined with wood or sheet, but it can be and is often applied to the underside of tiles. If you have felt which is cracked or torn then the foam will go onto it but this sort of backing is less than ideal. The best thing to do is to speak to a couple of installers first, then ask the Citizens Advice Bureau to direct you to an insulation advice centre for final advice before going ahead.

[buildersmate]

There has been considerable debate about this type of product over the years. Personally I think it is a daft idea because of the breathability issues. See some of the debate here and make up your own mind.
http://www.diynot.com...iewtopic.php?p=364468

[KARL]

Insulation is a bit of a mystery to the British public and heating is also sparsely used and the principal effects/interplay of the two hardly understood - the old remedy of maintaining draughts remains the norm for very many. Solid foam insulation is a vapour barrier but by its very nature it also does not give rise to condensation on its surface because the surface more or less stays at the temperature of the air touching it. If the insulation is not thick enough then the (inside) surface will cool down in cold weather, at which point the air at it starts to approach dew point. In almost all of the UK, if the thickness is as much as is required to sustain a temperature difference of 15 degrees Celsius between outside and inside with minimal heat transfer, then there should be negligible risk of adverse moisture buildup at any time within the house, including unoccupied roof space.