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Cavity Wall Insulation bridging DPC?

Discussion in 'Building' started by glock339, 31 Aug 2020.

  1. glock339

    glock339

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    I've just spent the last week or so cleaning out the 90mm wide cavities in an old cottage (aprox 100yrs), it took some doing as the crap was as a metre deep in some places. I'm now thinking of how to insulate, obviously CWI would be by far the easiest route although I know it can be a controversial subject as I've spent absolutely hours researching it & the info out there seems to be conflicting to say the least.

    The main thing that got me thinking though was the fact that the cavity obviously extends down past the floors & DPC which I have also just done so wouldn't this mean that the insulation beads could be sat in the damp bellow the DPC then transmit moisture upwards past the DPC? I know from having all the floors up that the dirt subfloor gets a bit damp in the winter, I sorted the old air bricks & installed new ones etc which helped a lot but it still gets a bit damp so thinking the bricks bellow the DPC be as well.

    Any thoughts appreciated.
    Cheers.
     
    Last edited: 31 Aug 2020
  2. JohnD

    JohnD

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    I had mine done with blown fibre. Unlike loft rolls, it is treated to repel water. I swept some up and put it in a bucket outside. After a rainy spell I lifted it out, the water drained away and it was dry.

    Loft insulation would have been like a wet sponge.

    So I don't believe it will support damp transmission by capillarity.
     
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  4. wouldn’t go near any of it.
     
  5. glock339

    glock339

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    I've seen some nightmare videos of the fibre insulation ringing wet being removed from cavities although I don't know if these were treated etc. I hear people say the beads in the bonded bead type insulation don't absorb water them selves but others say they can still come with potential problems. The more I look into the subject the more confused I become to be honest.

    Yeh seems to be a very divisive subject. The gable end is freezing in the winter so could do with something & the only alternative would be to internally insulate which would obviously be expensive time consuming & eat up valuable space which is at a premium in a small cottage. I had fibre CWI done in a previous property & luckily seemed fine for the 15 years I was there, but like I say after a bit of Googling on the subject it seems not everyone is so lucky.
     
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  7. Harry Bloomfield

    Harry Bloomfield

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    My semi, 1950's brick inner and outer leaf, concrete raft construction, I had CWI some 30 years ago. It was done by blowing in fibre via holes drilled every meter in the outer wall. No issues at all and it has made the house warmer. The only slight damp problem is a tiny area, on an interior brick wall, in the downstairs toilet, behind the toilet. It is so slight, I hid it from view rather than tackling it. Just a tiny bit of blown plaster on one side of the wall, plastered on both sides, so may not even be damp at all.
     
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