Dormer conversion insulation

[Dave Walsh]

Hey all, I need to get insulation for the attic. Its a Dormer conversion, now they insulated the slanted ceilings just not the tops or the sides (alcoves) of the upstairs. Now I hoping to use these as storage so I would need to insulate the roof out to the eves. Can you tell me what insulation to use and explain the vapour barrier to me, do I need one?. I was going to do something like; get the insulation inbetween the joices of the roof, leaving a few inches behind it to allow breathing, then staple a polyurathene sheeting across the joices as a vapour barrier. I was going to finish with some single ply boarding or something. Or should I just try slabbing and plastering it. I want it pretty clean in there..

Any information would be a great help

Thanks all

Dave W.

[sploop]

Could try a "stabbing" at english for a start

[Dave Walsh]

Don't top-post

DW

[John Rumm]

The ususal stuff would be foil faced urethane foam or polyisocyanurate (PIR) foam. Trade names like Kingspan, and Celotex are usually banded about.

To meet building regs insulation requirements you would typically stick

50mm between the rafters (leaving an air gap behind as you suggested), and then another 30mm right over the top. Finish with plasterboard and skim. Nett result id good insulation with loss of only 50mm ish of height.

Shop around for the foam, prices can vary by a large margin.

[Mike]

You can also get Kingspan to special order which can be skimmed directly which saves 10mm.

[John Rumm]

I thought that was just PIR foam/foil backed plasterboard? i.e. it would save some install time but the thickness would be much the same?

[Mike]

No - it's the foam covered with a sort of fireproof 'cardboard' with lots of holes in it for the plaster skim to grab on to.

[John Rumm]

OK, not seen that then... How does it compare price wise to separate foam and plasterboard sheets I wonder?

[Mike]

I bought a large quantity so was okay but special orders will be more expensive. Also it's nowhere as easy to get a perfect finish as the plasterboard covered stuff so for most people it's only worth doing if the head height is important.