Attic Insulation

BarneyMc

I'll soon be slabbing my FF ceiling. It's a cold attic and I plan on using 400mm mineral wool and a non-insulated plasterboard. I checked my energy report and it seems to only give a U value of 0.16 for this.

An older version had an insulated (50mm PIR) plasterboard along with 400mm mineral wool and gave a U value of 0.11.

Do these figures look right? I didn't really want to use an insulated plasterboard but with the difference in the U values maybe I should?

sydthebeat

That's probably using a fibreglass with a thermal conductivity of 0.044.

If you used something closer to 0.036 you'd probably get that down to around 0.12 u value

BarneyMc

sydthebeat wrote: »

That's probably using a fibreglass with a thermal conductivity of 0.044.

Spot on.

sydthebeat wrote: »

If you used something closer to 0.036 you'd probably get that down to around 0.12 u value

What is there out there that would get me this? Alternatively I could increase the 400mm? My guess is that these would be the cheaper options rather than going down the insulated plasterboard route?

Gumbo

Is the attic accessible? For storage use or any other?

BarneyMc

kceire wrote: »

Is the attic accessible? For storage use or any other?

Most will not be used for storage or anything.

sydthebeat

http://www.knaufinsulation.co.uk/products/glass-mineral-wool-rolls/loft-insulation-rolls/earthwool-rafter-roll

earthwool rafter roll comes in 0.036

http://www.isover.ie/products/isover-comfort-roll-35-wmk-0035
isover comfort roll @ 0.035

BarneyMc

I already have the 0.044 stuff bought but maybe I'll buy some of the better performing 0.035/6 stuff as an extra layer. Again my guess is that it would be the cheaper option to insulated plasterboard on ceilings?

Baggly

Metac is more readily available in my experience.

http://www.isover.ie/products/isover-metac-roll-wmk-0034

Also, when i was doing my parents attic, rang ISOVER for advice on the build up - they advised the additional layer, but did the calcs for me.

http://www.isover.ie/contact-our-technical-team

sydthebeat

BarneyMc wrote: »

I already have the 0.044 stuff bought but maybe I'll buy some of the better performing 0.035/6 stuff as an extra layer. Again my guess is that it would be the cheaper option to insulated plasterboard on ceilings?

do you NEED to reduce the u value??

400mm of any quilted material would be an excellent insulator

BarneyMc

sydthebeat wrote: »

do you NEED to reduce the u value??

400mm of any quilted material would be an excellent insulator

I guess not but will price the suggested products and see what it works out at.

For now I think I'll just put normal (non-insulated) plasterboard on the FF ceiling. There's a 45mm service gap between the plasterboard level and joists and would be weary of possible condensation build up anyway.