An architect has drawn up building regs drawings for a proposed extension a
nd the floor detail shows a vapour barrier both below and above the insulat
ion under the concrete slab. Is this normal/advised? I have only ever seen
the vapour barrier mentioned as going either above or below the insulation,
but never any mention of doing both (or explicitly not doing so for that m
I will of course ask the architect but wanted to also get a second opinion
in advance from the panel.
Is the correct answer. Though only necessary if 'open cell'
insulation like expanded poly is used. Closed cell insulation
like celotex could have a single DPM above or below it.
Infiltration of expanded poly with water and cement fines would
render it useless as an insulation, as does dropping expanded poly
panels loose into a cavity wall so that air can whistle past both
sides (and around the edges). I've seen lots of new build houses
on big-builder estate, built like this.
Vapour barrier is required on the warm side of insulation to prevent
condensation forming inside the insulation. However, in a floor, you
also need a damp proof membrane to prevent moisture soaking up from
the ground. So it doesn't sound like having one both sides is
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On Sunday, 22 July 2018 12:43:16 UTC+1, Andrew Gabriel wrote:
Yes, I did think it might have some advantages here. But then I also fear that if any moisture did find its way in then it'd likely struggle to get out again. I suppose that's not necessarily an issue.
I'll see what the architect says, and I might run it by the chap from building control too. They've already been through the drawings with a fine toothcomb but not mentioned anything about this.
On Saturday, 21 July 2018 22:26:40 UTC+1, Mathew Newton wrote:
and the floor detail shows a vapour barrier both below and above the insul
ation under the concrete slab. Is this normal/advised? I have only ever see
n the vapour barrier mentioned as going either above or below the insulatio
n, but never any mention of doing both (or explicitly not doing so for that
n in advance from the panel.
The Damp Proof Membrane is below the insulation.
The insulation is closed cell structure and has a foil covering and hence n
eeds no vapour barrier,.
The barrier above the insulation is to keep the wet concrete from corroding
the aluminium foil on the insulation and is usually quite thin.
Nonsense. The foil is only there to reflect long wave radiation where it
it used in walls or roof constructions.
Underground, the only thing that counts is the fact that it is
closed-cell, so doesn't need a vapour barrier on top.
Closed-cell insulation can go below the main DPC quite happily
bwcause water should not infiltrate it (in theory).
On Monday, 23 July 2018 21:58:48 UTC+1, Andrew wrote:
Is that so shit-fer-brains?
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