1810 house - French drain or Aco drainage - No DPC

Discussion in 'Builders' Talk' started by John Williamson, Sep 26, 2021.

  1. A recent damp and timber survey discovered raised external ground levels which are one of the things causing damp walls inside the house. Please note this house was built in 1810 and has no DPC. The surveyor suggests the following:

    Form a trench at the wall/path junction to a depth of 150mm below the physical damp proof course or internal floor level and fitting Aco drainage or similar, discharging into suitable drainage or back filling with pea gravel to allow drainage of rainwater.

    Any gravel filled trench should incorporate a suitable membrane against the wall surface and drainage so that water does not pool within the trench, which over time would penetrate to the full thickness of the wall contributing to internal dampness. Guidance on how to install such a membrane and drainage can be obtained from manufactures websites.​

    A couple of questions:
    1. I am leaning towards a French drain because it has more flexibility for getting around potential obstacles, is less permanent if things go wrong (rip it out and replace etc), and does not need to be physically fixed in place introducing more impermeable substances into the area with damp. Is this logic sound or am I missing something?
    2. Does anyone have an idea of what sort of membrane he may be suggesting? I can follow up with him but just wanted an opinion on here
    3. Given the age of the property and it's construction am I missing a trick where something else would be preferable?

    A few pics for reference attached
    listing_19222_0006_0adffc28_2560x1920.jpeg listing_19222_0008_9073d75e_2560x1920.jpeg
  2. hadfield

    hadfield New Member

    Hi John - how have you got on? I have a near identical issue in my new home and I'm very curious to know about the action you took. Check out the latest thread in my profile if you can. Many thanks.
  3. Still in the process of buying ours so afraid I can't offer any historical advice. The path I am going to follow is pretty much listed here:


    Someone on another forum suggested digging out and leaving it for a while whilst monitoring the inside which sounds pretty sensible.

    The other thing I will do concurrently is to get a dehumidifier to dry out the inside whilst hopefully reaping the benefits of the outside.
  4. hadfield

    hadfield New Member

    Thanks John. Appreciate the link too. I'm looking for a more immediate fix with winter approaching, though I appreciate the patience needed for a damp problem. I think I will take the trench approach without drainage pipe. Best of luck with yours.
  5. hadfield

    hadfield New Member

    hello again - coming back to you on a couple of your questions.

    Question 2.

    I’ve been looking at two products, a pretty cheap weed suppressing fabric and slightly more heavy duty driveway landscape fabric. I’m going to go with the cheaper option for now. Will let you know how I get on.

    Question 3.

    The amount of forum posts I’ve read and videos I’ve watched in recent weeks makes me believe that lowering ground levels is the ultimate solution to this problem. Modern attempts such as injection damp proofing, paint on sealant, poly based membranes and the like just do not address the root cause. If the original DPC is bridged by built up levels outside the property, the levels need to be lowered, either through a trench and adequate drainage around the perimeter, or total removal of concrete.

    JPJPJP New Member

    I have this exact same problem in an 1890s house I'm in the process of buying. Have either of you had quotes on the cost of the work per foot? I'm struggling to get anyone to give me quotes with just photos as they need to see the house. I'm just trying to get a ballpark figure for budgeting for the multiple issues that have shown up on my survey.

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