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Insulating the roof/walls of a dormer chalet style house.

I have a 4 bedroom Waites Dormer Chalet style house - think of a very large bungalow with 2 bedrooms and a bathroom built into the roof. These rooms are very cold, the walls are just boarded. Along both lengths of the house, on either side of the upstairs bedrooms, are very large eaves cupboards. The loft area above the bedrooms I plan to insulate with Rockwall (£3 a roll form b&q).

The roof area inside the eaves cupboards I plan to insulate using celotex between the rafters. The rafters are only 100mm deep so I plan to use 50mm celotex between them and then board over the top of the rafters with 100mm celotex holding into position by nailing it directly to the rafters and taping over the gaps. Is this the best way?

Thanks B J D Building and AJ Plastering. The roof in the eaves will have 150mm Celotex when finished although according to their website I should be able to get a building regs U rating using 50mm + 80mm Celotex.

The loft area above the bedrooms will be covered in 270mm of rockwool or equivalent.

One other question. A retired builder friend has built a stud wall at the gable end, each side of the house. The gabel walls as far as I can tell are just plasterboard, the exterior faced with tiles - I'm not sure what lies between.

Into the cavity between the stud wall and the original plasterboard he has stuffed rockwool but I cannot see any evidence of a vapour barrier. He has not used foil backed boards. Is this going to create a damp problem further down the line or will moisture pass through the exterior wall like I assume it did originally?

Thanks for your advice so far.

Graham

Ycoopeg20 7th Feb, 2012 Insulation
2 Answers u3
A

current building regulations is for 150mm celotex/kingspan insulatin or equivalant in the roof when upgrading more than 25% of a roof area etc. Could use celotex/kingspan together with a multi foil - this would give you your U Values but the thickness required would be less

As for stud walls on gable ends would need to see really, but if not caused any problems so far i'd say theres enough air flow etc so should be ok.

AJ Plastering & Building Services 9th Feb, 2012
A

Sounds okay, but dont use nails, use the appropiate board screws and plenty of them.

B J D BUILDING/ROOFING 8th Feb, 2012
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