Loft insulation

Norman_Castle

Insulation works by trapping air so compressing it reduces its effectiveness. Without an air gap above the insulation condensation can form.

Zither

glasgowdan wrote: »

I am about to do the eaves space in my loft as well. There are patches of old fibreglass insulation here and there but I want rid of the stuff as it's so horrible, so I'm going to bag it all up and bin it, then get 300mm of proper insulation in. The eaves covers probably 70% of the ceiling space of the downstairs kitchen, living room and 2x bedrooms, so it'll be worth doing.

In my case we have some built in storage so I will be adding it on top of everything that's there. In your case, if you think you might be rummaging about in the loft in future I'd get rid of the fibreglass stuff. It makes your skin itch like mad and is just horrible stuff.

I think it's worth putting as much as possible up there, so definitely get stilts for the boards rather than just putting in 120mm under them.

Thanks - any recommendations for any specific loft stilts? There seems a lot of different brands around and they’re quite expensive - eg 12 legs for £11 @wickes. My loft space is about 50sqm so I guess I’d need quite a few?

Also... are there any resources that quantify how much energy loss would be reduced from going from 110mm >250+ mm of insulation? I totally appreciate loft insulation is worth it but I wonder how much is diminishing returns?

Zither

Norman_Castle wrote: »

Insulation works by trapping air so compressing it reduces its effectiveness. Without an air gap above the insulation condensation can form.

Yeah that’s what I’ve read too. But then also read that people do it anyway and see an improvement and have no issue with condensation!

missile

Zither wrote: »

Also... are there any resources that quantify how much energy loss would be reduced from going from 110mm >250+ mm of insulation? I totally appreciate loft insulation is worth it but I wonder how much is diminishing returns?

That calculation would be very difficult. There are many variables which will change on a given application.

Suffice to say you should aim for a U value of 0.16 W/m2 K or less. In simple terms, 270mm insulation in two crossed layers to avoid thermal bridging.
See here http://www.rockwool.co.uk/technical-support/tools/U-value-Calculator/

Norman_Castle

Zither wrote: »

Yeah that’s what I’ve read too. But then also read that people do it anyway and see an improvement and have no issue with condensation!

I've compresses 6" insulation down to 3". No improvement in insulation. I did it just because its the easiest way to board the loft, I certainly wouldn't add insulation then compress it. If I had more time and patience reducing the compressed 6" insulation down to 3" would probably be an improvement.
Part of my loft is boarded with plastic coated chipboard. A few weeks ago after cold weather I lifted a few of these and they were wet on the underside.