pitched roof insulation ?

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Converting my flat roofed house to pitched roof ,with staircase and habitable room . All plans have been passed and approved , with gable end brick and block going up this week . My query is this , what is the best way to insulate the roof ? I have had a look on the internet and talked to other builders , but they all have differing opinions . The trusses are 200mm. x 100mm.
 
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The Building Regs changes very recently so this may be slightly out of date, but I used Celotex or Kingspan and installed 120mm. You need to leave an airgap of 50mm between the top of the insulation and the felt, and as my rafterswere 150mm deep I had 100mm between the rafters and then i ran cross battens 20mm thick beneath with insulation wedged between them.

Mineral fibre (Fibreglass) needs at least 250mm (Or did!) so that can't work even if your rafters were 200x100!

Swiss
 
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More like it, still a little more chunky than would be expected, but you are only at planning phase.
 
I've never seen attic trusses using 8 x 2 timber.
 
Thank you all , for prompt replies . The truss size of 8 x 2 , was specified by the structural engineer , 150mm. of insulation board would then give the required 50mm. of ventilation space .Two UB:s of 203 x 133 x 30 , supported by gable ends and tied together with three 90 x 90 x 8 angles , also built into wall ends . My main query , with regard to warm roof insulation , is will this amount of insulation satisfy the new up-dated 2006 Part L regs . The U value for roofs is now 0.16 ,will the above comply ? I do not wish to fall out with the building control chap . Grateful for any advice .
 
some kind of carpentered roof build, not trussed, I think, to accommodate the room..
 
Thanks again for your replies . The roof will be a cut pitched roof , with 8 x 2 rafters .
 
You seem to be planning to make a 'cold' roof. I would recommend a 'warm' roof instead which gives a lower minimum U-Value of 0.20W/m²K (instead of 0.16W/m²K for a cold roof) and you only need a 25mm space between the breather membrane and the insulation rather than 50mm.

What you need to watch for is cold bridging through the rafters. To make the U-value work you would need to fit 100mm of Celotex (or similar) in between the rafters and a countinuous layer of 30mm fixed below the rafters. Then fix a vapour control layer before boarding with plasterboard.

That will give you the required U-value and takes up minimum space.
 

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