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Loft Roof Insulation to Achieve 0.18 with 10cm Rafters

Postby elena2016 » Sat Jun 04, 2016 3:39 pm

Hello, please advise what is the most thinnest insulation on the market now so that I can use it for the loft roof (dormer and slope roof on the other side), where rafters are 10cm. So 5cm will be air gap, and I only have 5cm to play with and would like to avoid reducing the head height as much as possible. Thank you!
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Postby welsh brickie » Sat Jun 04, 2016 9:48 pm

triso super 10, is a quilt that is thin. you could try that.
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Postby MikeGrahamT21 » Tue Jun 28, 2016 9:56 am

You won't achieve 0.18U with 50mm of insulation, unless you used a Vacuum Insulation Panel (which are still very new, very expensive, and rather impractical for roof situations).

PIR is the most common material, with a lambda of around 0.021 at the very best, 100mm of this would give 0.21U. If you can afford the extra, Phenolic foam will give a slight reduction on the U value, but only slight.

Consider 50mm within the rafters and 50mm below, which would of course give around the same U value, but since the rafters would be covered, you will have reduced the effect of thermal bridging of the rafters themselves, which would give a better all round insulating effect.

Your final viable option, which again is more expensive is Aerogel ( ... el-blanket), which has a lambda of 0.014, meaning 100mm will give 0.14U.

What ever you do, don't use the multifoil insulation, if you read closely their stated U values can only be achieved by using PIR insulation as well as the multifoil. Its just a gimmick!

Hope this helps!
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