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1930's house cavity walls and solid floors, air brick in external leaf?

Discussion in 'Building' started by mic2876uk, 22 Jan 2019.

  1. mic2876uk

    mic2876uk

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    Hi Long time browser first time poster,

    Recently acquired a 1930's house with cavity walls.

    Previous owners had problems with damp and had DPM injected and cavity insulated. (early 90's)

    We have had most of the downstairs replastered during renovations and found some damp patches near the bottom of the walls, to combat this we fitted a mesh membrane system then dot and dab onto this. this seems to have worked well.

    In the hallway on an external wall we have not replastered and the existing plaster is also showing signs of damp at the bottom.

    in the 2 places where the damp was worse (hall and living room bay window) externally there is air bricks, these do no go all the way though and there is no signs they ever did.

    From what i have been told the reason we are getting damp at the bottom of the walls is due to debris in the cavity (no inspection made to confirm)

    My question is should i remove the air brick clean out the cavity and replace with a new air brick or a normal brick?.

    The house has concrete floors downstairs with original parquet on top which is in good condition with no signs of damp.

    Sorry for the long post
     
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  3. footprints

    footprints

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    I have a 1930's house with cavity walls and would never go near cavity insulation but that's another issue.
    Mine is the same, air bricks on the outer leaf not the inner as I understand it this is to provide air movement between the leaves to keep the inner leaf dry, the cavity walls are open in the loft so a good flow of air is available, blocking the cavity stops this happening.
    I would still keep the vents in your situation as they may also aid underfloor ventilation.
     
  4. sparkymarka

    sparkymarka

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    Our last house a 1930s house with a cavity had a damp patch in the kitchen near the back door , when we removed the door it was the cavity full of sand and debris, once cleaned out it dried out fine ...
     
  5. You don't need air bricks in the outer skin of brickwork to ventilate the cavity in order to keep the inner leaf of a cavity wall dry , you just don't need to ventilate the cavity. If there is debris bridging the cavity that could allow moisture across to the inner leaf , but how to investigate that and rectify if required ,perhaps others could advise.
     
  6. mic2876uk

    mic2876uk

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    Thanks all for the replies, this ties up with the information I had from a damp specialist i bought the membrane from (no site visit and I fitted membrane ourselves) The main reason we went for this option was we did not want to delay the plastering.

    I will remove the air bricks and clean the cavity as best as possible then replace the bricks with normal bricks.

    Does that sound like the best course of action?
     
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  8. What sort of cavity insulation is it? If you are clearing out debris you will need think how to to fill any voids with insulation !
     
  9. mic2876uk

    mic2876uk

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    upload_2019-1-24_21-46-40.png

    This is the stuff done by the previous owner due to the age of the stuff I imagine there are probably quite a few gaps by now
     
  10. There shouldn't be any gaps, they guarantee it for the life of the building ! I suppose it would invalidate the warranty if you start taking bricks out and clearing out any debris. Incidentally,they should have inspected the cavities to check there was no debris before installing the cavity insulation.
     
  11. mic2876uk

    mic2876uk

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    You'd hope so, some googling suggests not all companies did this.

    Also due the the open airbricks the wind would have blown in a lot of dirt over the last 25 years.

    Plus I imagine that when the double glazing was installed quite a bit of debris would have gotten in (fitted around 10 years ago)
     
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