Loft insulation

[zebedee2001]

Hi,

Probably been asked many times but specifics always makes you wonder if its applicable to your case:-

I am having to empty my loft due to getting it treated for woodworm. The loft is used heavily for storage & is boarded out throughout. It currently has 70mm of fibreglass insulation as that is the depth of the wooden joists.

I had a look at getting the insulation closer to standards & contemplated using CLS screwed the entire length of the existing woodwork to jack up the loftboards & creating a cavity for the loft insulation. I don't particularly want to use fibreglass again so had a look at the recycled bottle stuff. Both fibreglass & the bottle stuff has a lambda of 0.044 W/(m.K). I then looked at Celotex & notice that it has a lambda of 0.022W/(m.K).

1. So is Celotex twice as good as fibreglass?
2. Can I therefore get away with keeping my 70mm cavity & get twice the performance i.e. 140mm equivalent of fibreglass?
3. Is there a downside to using Celotex in a loft floor?
4. I assume the shiny side has to go down.
5. As Celotex doesn't compress will I apply pressure to the plasterboard below or am I best to jack up the floor a little to allow for flex & airflow below the loftboards?
6. Are there any better options I haven't considered that are itch free & keeps my storage space without losing too much head height?

Thanks for any help provided

 

[Charlie George]

Board insulation is hard to get into all the nooks an crannies in the loft area, and you also have to contend with wiring and lighting roses etc, one of the reasons loft rolls are used is for ease of use, you could look at getting the roof spars insulated instead.

 

[Koolpc]

Loft roll every time.

 

[Notch7]

1 yes pretty much although any gaps will reduce the effective u value

2 yes, see 1. Bear in mind current recommended loft roll depth is 300mm

3 as Charlie said, it’s pretty hard to fit and considerably dearer

4 it’s usually foil face both sides

5 you need to make sure the celetex sits below the top of the joists or you will push the ceiling plasterboard down

6 not really, I guess actis hybris will get you a better u value than glassfibre and easier to fit than celetex, maybe you could screw some timber battens on the joists and put in 100mm actis