Thermaline plasterboard or Kingspan + plasterboard

[dagoof]

Was wondering if anyone can help me. Pretty easy one - I'm about to start plasterboard lining my loft, however, I was advised by an architect to use insulated plasterboard on the internal cheeks of the dormer.

I've been checking the insulated gyproc out and it's quite pricey - however, I do have a quantity of 75mm kingspan left. I'm just wondering if it'd be possible to use that with plasterboard on top as opposed to buying the thermaline stuff? On the other hand, 75mm might be a little thick, what would typically be recommended for a dormer?

 

[freddiemercurystwin]

75mm is probably about right for compliance maybe..... //www.diynot.com/forums/viewtopic.php?t=185708

 

[dagoof]

Thanks Freddy - just thinking, in that case maybe I should bond the kingspan to the board with something?

Edit: actually, the kingspan could be put in between the battons (that form the dormer) to cut down on the thickness, but that would mean no air gap (the area's also disected a lot by the battons so that may cut down the insulation's effectiveness).

 

[freddiemercurystwin]

The insul should go between the studs to keep the thickness down and be the same depth as the studs with no air gaps, as you've mentioned there will be thermal bridging at the studs which is why 75mm may not comply. 100mm will I believe but 75 would probably need a calc to be sure. Get you're architect to phone Kingspan technical or do it yourself. http://www.insulation.kingspan.com/uk/services04.htm It may also depend on your BC inspector and whether he insists on exactly the right thickness and proof it complies if it looks a bit iffy. So you need to do all that before you install it.

 

[dagoof]

Thanks again for the info Freddy - it's not under building control at the moment. The loft conversion was started by the previous owner (had paperwork approved for it) and it had old fibre-based insulation. I've just ripped all that out and replaced with the 75mm kingspan. The architect I mentioned was just there regarding double glazing and was giving a few pointers. I don't see why there should be any problem as there was no insulation in the dormer before!

I've just checked and the dormer studs are 75mm so that should be spot on for the kingspan with no thermal bridge. Happy days