DIY Doctor UK DIY Forums

Hi, I'm really hoping somebody can advise me. I have a 1960's town-house so it has a bedroom in the 2nd floor roof space, at the sides of the room are eaves-lofts / storage space. The loft is what's been described to me as a cold loft which I understand to mean that it should have some natural ventilation from the outside, it also means that the top bedroom is very cold in winter.

My son will be moving into this room and as it has no central heating I need to improve the insulation. When I had a proper look I saw that the roof 'lining' was in very poor condition; the roof tiles sit on a brittle black layer of felt/tar-paper type stuff (between the tiles and the rafters) but much of that has fallen apart meaning that from the inside I can see the tiles and daylight so no insulation at all! I need a way of lining the roof between the rafters to prevent draughts coming in through the tiles but without encouraging condensation build-up.

Incidentally I've already insulated the floor and vertical wall so at least that's done.

I hope this makes sense, all advice welcome!

Hi Chuck21.

It sounds like you would need to replace the Breather membrane / Roof Felt before you go too much further with insulating. From what you have said, it sounds like it is possible to insulate between the rafters but you would need to consider the size of the rafter to ensure you have the correct air space for ventilation.

Rob

Many thanks Rob. I'd estimate the depth of the rafters as between 4 and 5 inches with a c.12 inch space between rafters.

I could tack breather membrane between the rafters easily enough; would there be any risk if I were to lay 25mm insulation board first (the dense polystyrene type)?

Cheers

ONLINE INSULATION wrote:Hi Chuck21.

It sounds like you would need to replace the Breather membrane / Roof Felt before you go too much further with insulating. From what you have said, it sounds like it is possible to insulate between the rafters but you would need to consider the size of the rafter to ensure you have the correct air space for ventilation.

Rob

Hi,

Yes, you could look at Celotex or simlar. Typically, you would need to leave a 50mm air gap between the roof felt and the insulation allowing a suitable air gap. Depending on if you are looking for a specific U-vale or not, you could look towards putting 75mm Celotex GA4075 between the rafters and a further layer of the same thing fixed to the under-side. This would give you a pretty good result. The GA4075 comes in 2400 x 1200 sheets that can be cut to suit. The layer between the rafters is friction fitted as long as you have something to hold it in place from below. the second layer is typically fixed and then taped on the edges with a foil tape for best practice. We have a website with both easy to use U-value calculators and Prices of materials if you are interested.

Regards,

Rob