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surface damp-proof membrane - effective?

  • 05-09-2014 9:02pm
    #1
    Registered Users, Registered Users 2 Posts: 5


    Hi all,

    background: we are building an extension at the rear of an old (c.100 years) house. during demolition one part of the existing floor, on which the new extension is to be built, has been found to be very damp - the actual concrete foundations are damp. we have been offered two choices: (a) dig up the floor completely and lay a new foundation; (b) simply lay a damp-proof membrane over the existing floor without digging down and laying new foundations. obviously (a) is the better option but it is much more expensive (2 grand) and we are at the limits of the budget.

    so here is the question: will the damp-proof membrane be effective in keeping out damp? we know there could be other problems e.g. small cracks in the floor later on. but the damp is the key issue for us. will the membrane keep it out - how effective and reliable are they?

    really grateful for any responses. many thanks!


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Comments

  • Registered Users, Registered Users 2 Posts: 78,580 Victor
    ✭✭✭✭


    What does your engineer say? Why is it "very damp" - is there a leaking drain? Higher ground?

    Comments like "very damp" suggests any hole or seam in the membrane is a potential problem.

    If you are at the limits of your budget now, can you afford to build?


  • Registered Users, Registered Users 2 Posts: 5 mert2248


    thanks viktor, much appreciated. engineer says it's preferable to do (a), but (b) is also possible though much less desirable. he identified two negative consequences: it could lead to cracks in the floor in the future, and the floor in that area would not be insulated. since we plan on laminate floorboards not tiles, I'm not sure how great a problem cracks might be. unfortunately I didn't ask him specifically about the damp itself and the effectiveness of the membrane in controlling it, stupidly enough. Things are moving fast, engineer won't be available now til Monday and builder is working through the weekend and could do with an answer asap. hence my post.

    from what you say then these membranes ARE liable to develop holes or rips that let damp through? and presumably cracks in the floor might mean rips in the membrane (or would it stretch to accommodate..?)

    many thanks again, much appreciated.


  • Moderators, Home & Garden Moderators Posts: 10,146 BryanF
    Mod ✭✭✭✭


    'A'


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