Loft insulation U value?

Postby TONYTONE » Mon Feb 18, 2008 1:10 pm

Hi guys,

I might be able to get my paws on an alternative form of insulation to use in my loft (kingspan cladding) and was wondering, building regs state that you need a minimum of 270mm insulation but what U value does this equate to so I conform?

Cheers in advance.

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Simply Build It

Postby Perry525 » Thu Feb 21, 2008 9:50 pm

The Holy Grail of 270mm of insulation is in relation to fiberglass.
However, fiberglass is a rubbish insulation for lofts as both water vapour and air move relatively easy through it and both of these equal heat loss.
This is why there has been a recent move to selling fiberglass in a thin plastic wrap - to avoid the wind sucking the heat out of our homes.
The best form of insulation and well above the requirements, is poly foam, poured between the joists, foam takes up the shape of the wood around it and seals off all the nasty holes that let the heat out.

The down side is that the joists between the poly foam then become cold bridges and you may be able to see their shape through the plaster and paint that cover your ceiling.

Draft proofing saves more heat than some forms of insulation.
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Postby TONYTONE » Fri Feb 22, 2008 12:51 pm

Cheers for that Perry525.

If i'm right on my research the 270mm insulation is based on a u value of 0.16(existing buildings). my reason for asking the question in the fisrt place is because i get my hands on allot of 22mm Kingsspan koolduct which has a u value of 0.021 per sheet. It may not fill in the gaps as well but its free so free. Exapnding foam should sort out any gaps, as for thermal bridging I'll have to see what I can come up with.

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Postby arbco » Sat Feb 23, 2008 4:47 pm

The 0.16 U value is correct and kingspan in layers will be able to achieve this with a number of layers. The value you quote for the kingspan would appear to be the r value (thermal transmittence) and not the U value. The 270mm is based allowing for the cold bridging of the timber joists in relation to the insulation hence fibreglass is often layed between the joists and then over in the other direction.

Look at kingspan products on their website and they should provide a thickness to achieve B Regs. About 120mm should be close of the top of my head.
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Postby InsulationBloke » Tue Nov 04, 2008 5:37 pm

Koolduct 0.021 is a K value not a U value
SO thats scuppered that plan, A U value is gained not only by the insulation used but the complete make up of the Construction.

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