Hi, I an insulating my attic and need to put 40mm of kingspan inbetween rafters and an extra 60mm under the rafters. The queston is because with two seperate boards I would have 4 layers of foil rather than just two layers of foil if i was to use a 100mm board for instance. Would 4 layers of foil increase the thermal value. The reason being is that I was thinking of just having the 40mm in the rafters and then the insulated drylining board at 60mm under the rafters. Though i think two foiled boards would be better.
thermal properties of layers of kingspan
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wouldn't have thought so - the foil is there to protect the surface of the board and to reflect heat, not insulate. the r value of 100mm is the same as the r value for 50mm.
have a play with this http://www.celotex.co.uk/Technical-Services/Further-Information/U-value-Calculator
have a play with this http://www.celotex.co.uk/Technical-Services/Further-Information/U-value-Calculator
Just ring their techy helpline they won’t mind you running a few different scenarios past them!
0870 850 8333
0870 850 8333
Foil has lower emissivity than most other materials so does add a small value to the overall insulation. That's what multifoil insulation is all about.
Doesn't work if the foil layers are touching though. You need a gap. So in your case you will get no extra value from the additional foil.
Doesn't work if the foil layers are touching though. You need a gap. So in your case you will get no extra value from the additional foil.
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A sealed reflective cavity at least 20mm deep is roughly equivalent to 15mm PIR. Both have an R-value of about 0.6. If the foils are in contact with other materials, they lose their insulation potential. A smaller cavity has a lower R value.
The foil against the tiles effectively form a vented reflective cavity and is roughly equivalent to 10mm of PIR or an R value of 0.4. However, this foil is likely to pick up dirt and lose its low emissivity.
The foil against the tiles effectively form a vented reflective cavity and is roughly equivalent to 10mm of PIR or an R value of 0.4. However, this foil is likely to pick up dirt and lose its low emissivity.
where are you thinking of putting the 100mm boards if in between the rafters then this will not be up to the job due to thermal bridging created by the rafters, if under the rafters then it will be fine but you will have difficulty fixing that and your plasterboard to the rafters
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