Floor insulation - AIRTEC foil gap

Discussion in 'Floors, Stairs and Lofts' started by fozzy9876, 20 Nov 2021.

  1. fozzy9876

    fozzy9876

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    Hi,

    I need to insulate under my suspended floor and thinking of doing the following:
    • Breathable membrane stapled to underside of joists to prevent wind wash
    • 100mm PIR board. Gaps sealed with foam/tape
    • Over the joists/PIR, YBS AIRTEC REFLECTIVE double foil as (admittedly expensive) vapour control layer
    • Floor boards, underlay, carpet
    YBS will help insulate if there is an air gap. For this reason I was thinking rather than having the PIR boards flush with the top of the joists, dropping them slightly to leave a 15mm gap between them and the foil. Has anyone done this, does this sound sensible?
     
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  3. Mr Chibs

    Mr Chibs

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    There’s a lot of differing opinions on using membranes on here:cautious:

    I used rock wool, full depth of joist. With a building paper on top, then floorboards.

    If I was using foam boards, I’d leave no gap, and bring to the top of the joists.
     
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  4. fozzy9876

    fozzy9876

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    Thanks. I think keeping it flush we the the joints is best. I have some spare rock wool which I might fill the 20mm gap between the PIR board and the breathable membrane. Probably a bit pointless, but every little helps I guess.
     
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