no insulation in roof....

[goofy gorilla]

hi - a few years ago i had my loft converted into a bedroom, the bloke who done the conversion never put no insulation in the roof before he put the plasterboards on...now im a bit wiser and older, notice that all the heat is being lost through the roof, and its very cold, im going to remove the plasterboards and put some insulation in..just a few questions:

whats the best insulation to use and what size ?

would i need to put some battons on the inside of the roof beams so that the insulation and plasterboard have a gap betwwen them to allow for air circulation?

whats the best plaster boards to use ?

im not going to get the ceiling replastered again, im hoping to put some kind of ceiling covering over the plasterboards and paint the ceiling or even put ceiling paper..

any advice would be great..ta

 

[noseall]

120mm* celotex or kingspan insulation boards with 25-50mm airgap above the insulation and below the roof membrane.

*80mm between rafters and 40mm underdraw.

 

[goofy gorilla]

120mm* celotex or kingspan insulation boards with 25-50mm airgap above the insulation and below the roof membrane.

*80mm between rafters and 40mm underdraw.

so what you saying is a 25-50 mm gap between the plasterboard and the insulation..and also a 25-50mm gap between the insulation and roof membrane????what do you mean when you say "40mm underdraw"?...ta

 

[noseall]

just the one air gap - above the insulation (or below the felt, depends how you look at it).

underdraw: a layer across the underside of the rafters i.e. where the plasterboard is fixed. obviously, once you have fixed the inso' then you will need longer fixings for the plasterboards.

 

[chappers]

or 100mm mineral between with tri-iso under rafters would be a much cleaner job, although having said that you are going to have to pull the existing ceiling down anyway, also did you have a dormer constructed as the specs for a flat roof are a bit higher too.
With regards to your plasterboard you could use tapered edged boards and fill the joits, Have a look on the lafarge website in their drylining handbook.

 

[noseall]

are building control sanctioning the use of tri-iso now?

 

[chappers]

Our BC here in Oxford are happy with the spec I have given for a pitched roof. the last loft I did a month or so ago was speced with just tri-iso and BCO asked for it to be backed up with 100mm of mineral as they were no longer sanctioning tri-iso on it's own
I believe some local authorities aren't allowing it's use at all, seems to vary from one authority to another from what i can see.
The loft we are currently doing is on the other side of town and within a different local authority I asked the BCO if we could use the same spec instaed of celotex and he didn't seem very pleased with the idea.