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General: Damp Problem

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  1.  
    Is the damp inside on all the affected walls or just in one place?
    Is there damp inside both properties or just one?
    Could it be a terrible coincidence? e.g. a leak inside that coincides unluckily with the efflorescence on the outside?

    Having said that, the window sill is very green. It suggests very much that the gutters are overflowing down the walls. I have a pvc window sill on a north-facing flat-roofed bathroom that rarely gets cleaned (even though it is single storey so is at ground level!) and it's not as green as that. It did grow some moss at the ends though.
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      CommentAuthorfostertom
    • CommentTime11 hours ago
     
    Posted By: djhAnd effluorescense on the outside doesn't account for damp inside.
    Oh, I think it does. Efflorescence requires a steady supply of water into the brick (slips), before same can be steadily drawn to the surface. Maybe just impinging rain water, uniform but manifesting as efflorescence only where the brick (slips) is salt-laden. Internal damp implies that the water supply is pretty much a flood, into both masonry leaves and the EWI zone, coming from top down.
  3.  
    The cavity in the wall is (presumably) a continuous/connected space across each face of the building but (presumably) there are fire barriers dividing the cavity where the two semis meet

    So the cavity can be wet on one property or elevation and dry on the adjoining one? Hence the efflorescence one side and not the other.

    Question whether the cavities are still open and ventilated and acting as safe drainage planes as originally built, or whether they are filled/blocked, on each elevation?

    If (some of) the cavities are filled and their weep holes blocked and they have been covered with impervious brick/cement, then there's nowhere for moisture to escape once it gets in. Eg if it gets in from dubious gutter detail, or from driving rain or humid internal air.

    There are some parts of the country where cavities should not be filled because of driving rain.
    • CommentAuthorrevor
    • CommentTime10 hours ago
     
    Posted By: WillInAberdeenThere are some parts of the country where cavities should not be filled because of driving rain.


    Totally agree. There have been much publicised horrendous problems here in North Wales. When we were doing our build and looking for a brickie I went to see a short listed one on a job. He was almost up to the eaves with a cavity wall and when I asked why no insulation he said it was going to be blown in after construction. I passed this by our BCO and he said it although it would be an approved filling he would advise against it. The house we went to see was in an exposed area and I sometimes wonder how it faired.
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      CommentAuthorfostertom
    • CommentTime10 hours ago edited
     
    The great thing about EWI is that it's been found, for over half a century in N Europe, and a bit less in UK, to be extremely reliable and problem-free, in fact elegantly solving typical other housing problems like mould, penetrating damp.

    It takes a magnificent effort to mess it up, as in cheapskate schemes in UK, govt funded in a way custom designed to attract cowboy profiteers without any quality control, such as we see here, to create a body of typical problems and a bad reputation (just like with heat pumps) in the media/public mind.
  6.  
    There's a big distinction (at least in building regs) between impervious render that sheds rain, versus a masonry finish with recessed mortar joints


    The English building regs AD C have a map that also covers Scotland and Wales

    The high risk zone 4 is West Scotland, Cumbria, N and W Wales, Devon+Cornwall

    The low risk zone 1 is from London up to York and Norwich

    Full fill cavity with recessed-mortar-joint finish is allowed only in Zone 1 but not Zones 2-4

    Full fill cavity with render finish is allowed anywhere - but not zone 4 with narrow cavities or injected foam

    Other fills and finishes, and other zones, have intermediate rules


    Isn't clear how this applies to brick slips on EWI on a filled cavity.

    In the OP's case we don't know if rain is getting into the cavity from the top or the outside or inside so might not be relevant to them.


    ETA agree with Tom's comment about cowboys ruining the funding schemes due to abysmal oversight- scandalous - the problems often with dodgy eaves details. Was the OP's building done by one of those schemes, redress may be available?
    • CommentAuthorrevor
    • CommentTime5 hours ago
     
    Posted By: WillInAberdeenFull fill cavity with render finish is allowed anywhere - but not zone 4 with narrow cavities or injected foam


    Here in Anglesey (Zone 4) a rendered cavity wall must have a 50 mm gap between the outer wall and the insulation. It is also permissible for there to be no weep holes over lintels. If it is a brick finish outer wall the gap should be 75mm.

    Posted By: WillInAberdeenIsn't clear how this applies to brick slips on EWI on a filled cavity.


    Probably a much greater risk of penetration of water into EWI than a full brick. (100mm v's a 10mm slip or thereabouts). Instinctively I do not think brick slips are a good idea over EWI even though the subject is covered in some depth in Pearson’s book External Wall Insulation as a suitable cladding. Recessed pointing is only recommended on the thicker slips and the pointing to be a specialised waterproof coloured mortar..

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