Loft Extension Insulation

[leevis]

Hi
I am currently doing a loft extension and i need clarification on the thickness/type of insulation required legally.
I have heard that it needs to be 100mm thick but does it have to be a certain type ie insulation board or polystyrene or that roll stuff?
Obviously i would like the board but it is way expensive, like £30 for 2.4mx1m and the polystyrene is that much cheaper.
Anyone know exactly what i should use and the most cost effective method? This insulation is to go between the ceiling joists.
Thanks
Lee

 

[^woody^]

Anything other than celotex/kingspan will be impractical as it will need to be really thick

Its not just a case of being 100mm thick, you need some between the rafters and some across the underside (or outside) of the rafters to form a continuous layer. How much of each will vary.

You may also need to maintain a 50mm air gap below any felt - so this may determine the insulation board sizes

 

[noseall]

This insulation is to go between the ceiling joists.Thanks
Lee

hey woods can't you read.

you will require a minimum total 270mm thickness of *fibreglass insulation between joists and across, in the loft.

this can be done with say 150mm between the joists and another 150mm layer across the joists. ok, you will end up with 300mm, more the merrier i say.

*edited to add fibreglass.

 

[Eng33]

When you say you're doing it "legally", I assume you mean to the relavent building regulations, which in this case is covered by Part L1b. If you notify this work to your local authority, the required amount of insulation will be dictated by the total U value of the combined surfaces, i.e. plaster board + skim, insulation, air gap diatance, etc. The two main insulation manufacturers Kingspan and Celotex have very useful help lines that will tell you what thickness insulation you require for your given situation.

 

[^woody^]

This insulation is to go between the ceiling joists.Thanks
Lee

hey woods can't you read.

you will require a minimum total 270mm thickness of *fibreglass insulation between joists and across, in the loft.

Yes I can read you can't

Its a loft conversion, he don't need 270mm in the floor

Anyway, I took it that the ceiling joists will be the new ceiling joists ie the rafters!

If he means the floor, then its 100mm rockwool, nothing else - its for fire resistance. And on chickenwire too.

Note to self - use BIG font on noseall's plans in future. lol

 

[noseall]

Note to self - use BIG font on noseall's plans in future. lol

aye.