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Housing - Renovation: Reducing thermal looping in an existing wall while preserving semi cavity

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  1.  
    • CommentAuthorwholaa
    • CommentTimeJun 8th 2020
     
    I have a situation with a semi cavity wall with 110 mm PIR of a completed house. I am doing some work on the reveals and now that the blockwork is exposed it allowed me to realise that there is a cavity between the inner leaf and PIR boards, ranging from 2mm to 10mm. I guess the block layers were messy and didnt clean the beds enough so the PIR boards cant sit right against the inner leaf. It seems like there is thermal looping in action, even in the mild June weather. Given that some of the blockwork is exposed, would it be appropriate to try to fill this cavity with foam beads and diluted PVA to reduce the gap? This would hopefully preserve the cavity on the outer leaf face, so the wall doesn't become full fill.
    Are there risks attached? Is expanded glass beads better?

    ___
    • CommentAuthortony
    • CommentTimeJun 8th 2020
     
    I think that you can buy small size beads 1 to 2mm in size rather than the more normal 4 to 8mm

    I would use tiny beads if you can get them. Treat with pva, dry them, pour them in, they will stick themselves together after a while
    • CommentAuthorwholaa
    • CommentTimeJun 8th 2020
     
    Posted By: tonyI think that you can buy small size beads 1 to 2mm in size rather than the more normal 4 to 8mm

    I would use tiny beads if you can get them. Treat with pva, dry them, pour them in, they will stick themselves together after a while


    Thanks Tony. There is no fire risk or anything of the sort?
    • CommentAuthortony
    • CommentTimeJun 8th 2020
     
    I can neither confirm nor deny but I do have similar beads in some of my cavities
    •  
      CommentAuthordjh
    • CommentTimeJun 8th 2020
     
    EPS sheets are treated with a fire retardant during manufacture. (I put a blowtorch on some to test it works). I don't know about beads.
    • CommentAuthorwholaa
    • CommentTimeJun 9th 2020
     
    I found a 0- 3mm foam glass 40 litres available for just 20 pounds so I may invest in that. The only worry is might blow the PIR off the walls.
    • CommentAuthorMike1
    • CommentTimeJun 9th 2020
     
    I guess an alternative would just be to seal the top of the insulation, which would at least stop easy interchange with the external air.
    • CommentAuthorwholaa
    • CommentTimeAug 7th 2020
     
    Hi all,
    I was working on this window again. I tried to seal it with tufts of earthwoold and then poured in 1-2mm EPS beads. It's somewhat perilous as they are easy to inhale because they are extrodinary prone to being blow around. This makes them hard to work with but excellent for spotting draughts. When I had some windy weather I found it remarkable how clearly these beads could show windwashing of the insulation boards. See video

    https://imgur.com/edvLFZN

    https://imgur.com/QVeTG9g

    I will have to just add a more glue and then seal with a windtightness or airtightness tape.
    This window is on the windiest side of a very wind exposed house. There are some vents in the walls to vent the cavity see here
    https://imgur.com/to7iXX2
    https://imgur.com/5TMQuzc

    But I wonder is there a formula to calculate how many vents are needed given local weather conditions? I wonder if I have too many and I could reduce the wind washing by blocking a few? I will also try to seal around my meter box too which is letting air in.
    •  
      CommentAuthordjh
    • CommentTimeAug 7th 2020
     
    Posted By: wholaaIt's somewhat perilous as they are easy to inhale because they are extrodinary prone to being blow around.

    That's what face masks are for (among other things). :bigsmile:

    There are some vents in the walls to vent the cavity

    Are you sure they are vents rather than drains?

    Sorry, I don't know how many there should be, except drains above every lintel etc.

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