Insulating Between Rafters on Dormer Bungalow

Fujitsu10

I am considering insulating between the rafters in my dormor bungalow, I dont want to remove and replace all the dry lining etc. My plan was to remove the roof tiles and fit insulation board between the rafters. The rafters are 110mm x 45mm.

A few questions I have that you might be able to help me with:

1 Do I need to maintain a gap of 50mm between the top of the insulation board and the roof felt?
2 Can anyone recommend a board type (thickness etc) and installation method for the best possible result?

Any suggestions would be most welcome.

Carlow52

Very Interesting idea.

I, if doing this work would give serious consideration to running the insulation across the rafters as opposed to cutting and fitting between them.

Its very difficult to get right.

If the roof is fully sheeted inside then it might be possible to get an foam sprayed in

see here just for the idea
http://www.youtube.com/watch?v=8fS8PiZ_Xvk

The foam chosen will need to be breathable

I recognize that this is more work as in fact you may need planning to raise the roof by the thickness of the insulation but it will, IMO, lead to a much better job especially from an air-tightness perceptive.

even if u fill the full 110 its not going to be enough in my view

The 50mm gap is only required if the 'felt' under the slates is not breathable so you should price in for breathable roofing felt.

You should also price in replacing the slating laths as its tough to get them off.
How old is the house?

ps: I got a quote a year or so ago for doing the outside idea for a bungalow with 18m by 10m foot print: it was 16-20k just for material

Fujitsu10

Carlow52 wrote: »

Very Interesting idea.

I, if doing this work would give serious consideration to running the insulation across the rafters as opposed to cutting and fitting between them.

Its very difficult to get right.

If the roof is fully sheeted inside then it might be possible to get an foam sprayed in

see here just for the idea
http://www.youtube.com/watch?v=8fS8PiZ_Xvk

The foam chosen will need to be breathable

I recognize that this is more work as in fact you may need planning to raise the roof by the thickness of the insulation but it will, IMO, lead to a much better job especially from an air-tightness perceptive.

even if u fill the full 110 its not going to be enough in my view

The 50mm gap is only required if the 'felt' under the slates is not breathable so you should price in for breathable roofing felt.

You should also price in replacing the slating laths as its tough to get them off.
How old is the house?

ps: I got a quote a year or so ago for doing the outside idea for a bungalow with 18m by 10m foot print: it was 16-20k just for material

Thanks for the reply, firstly the house was built in 1991. I didnt mention that I'm only planning doing the entire front section of the roof as we built an extension to the rear of the house 2 years ago and insulated this at the time. There is just a small section at the rear to be completed. If I raised the height of the roof then I would have trouble matching it to the rear of the house.
On the subject of "breathable" felt, can you recommend any type? and if used can the rafter space be filled right up to the felt?

paddy147

Im about to have my attics insulated with an open cell spray foam insulation.

Can I ask,is it ok to spray foam in electric cables and plumbing pipes for the bathroom,that are in the roof space??

Would covering them in spray foam mean that they wouldnt have to replaced in say 20-30 years time.

Thanks.

gsxr1

paddy147 wrote: »

Im about to have my attics insulated with an open cell spray foam insulation.

Can I ask,is it ok to spray foam in electric cables and plumbing pipes for the bathroom,that are in the roof space??

Would covering them in spray foam mean that they wouldnt have to replaced in say 20-30 years time.

Thanks.

Im sure it was been covered here in past posts here.

Im not sure it is ok to foam or insulate over wires. I have been pulled up by electricians before, for not cutting an appropriate size cavity channel for wires in kingspan type wall insulation.
I believe it is down to heat build up on electrical items that draw lots of current. With fire as a worst case senario.