yes indeed -apologies for incorrect terminology
BR specific to warm roof designs?
- Thread starter d000hg
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Leofric
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Would be quicker and more accurate to look at the BBA certificate or the data sheet!
We took the view that products like Visqueen at 50p/m^2 and so easy to fit, one might as well put it in as argue about it.
That said, a VCL should only be needed if the prior surface is not airtight? So if you plaster your ceiling for instance?
That said, a VCL should only be needed if the prior surface is not airtight? So if you plaster your ceiling for instance?
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Every material has a certain vapour permeability and thermal resistance.
Basically if you want to get scientific about it you can calculate based on the predicted internal temperature and humidity and the outside temperature, whether you're likely to get interstitial condensation anywhere in the buildup.
Generally if you go from less permeable to more as you go out, you'll be ok.
Plaster I've no idea how resistant it is, depends if it's on foil backed boards and whether there are sockets in it, but yes it does have a reasonable vapour residence.
The gold standard is a plastic sheet, although an allowance is made for penetrations and leakage it will deal with most situations.
Hope that is clear (!)
Ps don't confuse airtightness with vapour permeability
Basically if you want to get scientific about it you can calculate based on the predicted internal temperature and humidity and the outside temperature, whether you're likely to get interstitial condensation anywhere in the buildup.
Generally if you go from less permeable to more as you go out, you'll be ok.
Plaster I've no idea how resistant it is, depends if it's on foil backed boards and whether there are sockets in it, but yes it does have a reasonable vapour residence.
The gold standard is a plastic sheet, although an allowance is made for penetrations and leakage it will deal with most situations.
Hope that is clear (!)
Ps don't confuse airtightness with vapour permeability
It would be quicker for me to go and fetch one from the moon by walking, than to wait for a reply.
L
Leofric
No, just look at the BBA certificate or the data sheet.
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