Is there any reason not to use 300mm of loft insulation rather than the
270mm specified?It actually would be cheaper to use 3x100mm layers than the normal 100mm layer with a 170mm layer on top as there would be no waste left over.
Adam
Adam
None whatsoever - the specifications for the thickness of loft insulation changes according to the thinking of the day, and when my house was built in the '70's, the loft was covered with a layer 1/2" thick - it's now 300mm.
NB: Just try and keep cables that supply any electric shower above the insulation - or if that is not possible, leave it free in a 'valley' in the insulation.
Cash
Dont you rate it by R value, so what are you buying? In the US we do. Different types of insulation have different values and it goes from R
3" to R 7.2" fpr polyisocyanurate foam. Many types settle up to 20%, Code for me is minimum R 35 attic and I have R 100. Did you know Fiberglass looses about 20% of it R value at 10f? Codes are minimums depending on type and how cold your area is, and figure in settling maybe 450mm is correct for you. 300mm is about 12" or R 45 which is ok if it doesnt settle or get real cold where fiberglass looses R value.
On this side of the pond we use U-values, which are the reciprocal of the sum of the R-values. That way we can trade-off heat losses, and take account of thermal bridging. We use metric units, rather than imperial, so resistance is measured as metres^2.degrees Kelvin/Watts. The maximum U-value for roofs is 0.16W/m^2K (or less depending on the overall carbon emissions), which is a R-value of 6.25m^2K/W, of which the insulation (plus ceiling joists) would need to be about 5.86m^2K/W. How that relates to your imperial units, I'm not sure.
I put 3 layers of 100mm down. Just 50% extra work. But no waste.
Adam
Thank you for allowing me to make the correction. After, "How that relates to your imperial units", replace text with, "I can't be arsed to look up".
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