Who to hire for damp at the bottom of a wall

Short answer

A builder or a damp specialist — but insist on a diagnosis before a treatment. Damp at the base of a wall has four common causes: ground level built up above the damp-proof course, a leaking pipe or drain, poor sub-floor ventilation, and genuine rising damp through a failed or absent damp-proof course. The first two are much more common and much cheaper to fix than the fourth, which is the one most often sold.

Plan itThere is time to get more than one quote, which is where the money is.

When it is someone else

Calling the wrong trade costs an attendance fee to be told so. These are the cases where this problem belongs to someone other than a Builder.

  • a plumber

    a drain, a downpipe or a water service runs near the affected wall.

  • a landscaper

    soil, paving or a garden bed sits above the damp-proof course. Lowering the ground is often the entire fix and it is the cheapest one.

What to do before anyone arrives

  1. Go outside and look at the ground level against the wall. There should be a visible gap between the finished ground and the damp-proof course line in the brickwork. Paving and garden beds built up over the years are the single most common cause.
  2. Check where downpipes discharge and whether the ground falls away from the house.
  3. Look at the subfloor vents if the house has them. Blocked or covered vents stop a subfloor drying.
  4. Note whether the damp is seasonal, constant, or appeared after something changed outside.

What to ask when you book

  • What is your diagnosis, and what measurements support it?
  • Have the external ground levels and drainage been checked first?
  • If you are proposing a chemical damp course, what happens to the salts already in the wall, and is re-rendering included?
  • What warranty is there, and what does it exclude?

What changes the price

No dollar figures here: this directory holds no price data and an invented range is worse than none. What follows is what makes one of these jobs cost more than the same job next door, which is the part you can actually use when comparing quotes.

  • Whether the fix is external — lowering ground, fixing drainage, clearing vents — or internal.
  • Whether render and plaster have to be removed and replaced, which is usually the bulk of the cost in a real damp course job.
  • Length of wall affected.

What you can do yourself

Is this licensed work?

Structural and waterproofing work is building work and licensed above a threshold. Chemical damp-proof course injection is not separately licensed in most states, which is a reason to be careful who you buy it from.

There is no national register. Search the licence number with the regulator for the state the work is happening in.

Licensing thresholds and certificate requirements differ by state and change with amending regulation, so this page describes the mechanism rather than quoting a figure. The regulator’s own page is the current answer.

Common questions

Who should I hire for damp at the bottom of a wall
A builder or a damp specialist — but insist on a diagnosis before a treatment. Damp at the base of a wall has four common causes: ground level built up above the damp-proof course, a leaking pipe or drain, poor sub-floor ventilation, and genuine rising damp through a failed or absent damp-proof course. The first two are much more common and much cheaper to fix than the fourth, which is the one most often sold.
Is rising damp real?
Genuine rising damp exists and is well documented in older buildings without an effective damp-proof course. It is also diagnosed far more often than it occurs, because the symptom — damp at the base of a wall — is shared with several more common and cheaper causes. The test is whether anyone checked those first.
Why does the paint keep bubbling at the skirting?
Moisture moving out through the wall carries dissolved salts, and those salts crystallise behind the paint film and push it off. It is why painting over damp always fails and why salt-attacked render usually has to come off rather than be sealed.

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Who to hire for

General information about who does what, not advice about your specific job. Licensing, consumer law and council rules differ by state and change; the regulator for your state is the current source. More guides to hiring a tradesperson.