Pitched Roof insulation

[headworx]

Hi all,

Just had a new extension 3mx5m. Pitched roof with breathable membrane fitted with Marley Moderns. The rafters have enough space for 170mm I believe ( want a bit of space to run cables though)

Now looking for the insulation to fit in there.

Any recommendations on whats best or they all the same pretty much? (celotex,kingspan,xtratherm etc)

I think the building regs person said they have to be 150mm to achieve the required U value? Think I have to achieve 0.18 U value?

I was thinking 100mm first, then a 50mm over that, then board. Or maybe 2x70mm. Depending on prices etc.

If anyone knows of the cheapest place to get them I would appreciate that too. (trade or public).

Edit.....Sorry one last thing, I presume I'm looking for a board thats foil backed both sides to minimise condensation? Thanks

 

[freddiemercurystwin]

The products you have suggested are all much of a muchness and the selection of the final manufacturer/thicknesses just depends on availability and price. You could try Encon or many on here favour ebay for factory seconds etc for their insulation.

If you use foil backed plasterboard you don't need any foil faced insulation. The object is to prevent any moisture entering the insulation so the vapour barrier needs to occur behind the plasterboard. If you opt for foil faced insulation you should tape the joints with aluminium tape. Alternatively you could just use polythene sheet vapour barrier instead.