Damp, mould and defects

What is ‘damp’ in buildings?

Damp can be described as ‘excess moisture that should not be there’. This guide explains which symptoms are worth investigating, the three different ways moisture moves through or onto a building, and the defects that let it in — including why a diagnosis of ‘rising damp’ is so rarely the answer.

What Causes Damp

Damp staining and mould spreading across the wall of a UK home

When to investigate

Excess moisture that should not be there.

If any part of your home is not dry to the touch, has mould growth or has a musty smell, you should investigate. Any one of the three is enough on its own.

Not dry to the touch

A wall, floor or ceiling that feels genuinely damp rather than simply cool — often with paint lifting, wallpaper bubbling or plaster crumbling behind it.

Mould growth

Black or green spotting in corners, on window reveals, across ceilings, or behind furniture pushed up against an outside wall.

A musty smell

An earthy, cellar-like smell that comes back a few hours after the room has been aired and shut up again.

Different forms

Damp comes from many sources and takes different forms.

You will hear three terms used for damp: penetrating damp, condensation and ‘rising damp’. Each describes how moisture is moving through or onto part of the building.

Penetrating damp

Water passing horizontally into the building from outside — through the roof, the walls, the windows or the doors. It usually follows the weather, showing up during or shortly after driving rain and fading between spells.

The moisture is arriving through a defect in the fabric, so the useful question is always which defect, and where.

Condensation

Water vapour produced inside the home settling as liquid water on surfaces that are colder than the air around them — windows, external wall corners, cold spots behind furniture and the coldest parts of a ceiling.

Here the water is generated indoors rather than getting in from outside, so the balance of moisture production, ventilation, heating and surface temperature is what decides whether it appears.

‘Rising damp’

A term often misused to describe moisture that has moved vertically upwards from the ground below by capillary action or suction — like a sponge sitting in a puddle, slowly soaking up water through the tiny holes inside it.

It is often misdiagnosed. A typical misdiagnosis would be that ‘rising damp’ is the cause of your problem and that your home needs a new damp-proof course.

Why ‘rising damp’ is not a diagnosis

‘Rising damp’ is not a conclusion, as it does not identify the source of the excess moisture.
Failure of an original damp-proof course is extremely rare.
A new damp-proof course prescribed without a diagnosis treats a symptom that may not even be present.
Ask for independent advice before agreeing to any remedial scheme, particularly one quoted by the firm that carried out the inspection.

Penetrating damp, ‘rising damp’ and condensation are not causes of damp but are different ways moisture moves through, or onto, parts of a building. To solve a damp problem, you first need to find where the moisture is coming from.

What causes damp?

Start outside, in the rain.

Finding the cause(s) of a damp problem can sometimes be complex, and it is best to contact a specialist building surveyor and ask for a Joint Position Statement (JPS 2022)-compliant survey. However, anyone can investigate and look for problems. For example, you could go outside in the rain and see whether your gutters are overflowing. If something doesn’t look right, it usually isn’t right.

Roof and rainwater

Leaking and/or blocked gutters and rainwater pipes.
Roofing defects, such as poor roof flashings and dislodged or broken roof tiles.
Open chimney pots.

Walls and openings

Poor external pointing.
Cracked external wall render.
Ill-fitting doors and windows.
Broken sealant or mortar around windows and doors.
Bridged cavity walls, i.e. physical blockages such as rubble in the cavity wall void.

Ground level and under the floor

Raised ground levels next to walls.
Excess rubble under suspended ground floors. This can stop ventilation under the floor and make floor timbers wet, bridge the damp-proof course and block low-level through-wall air vents.
Blocked low-level through-wall vents for suspended floors.

Water, drainage and plumbing

Failed underground drainage.
Leaking water main supply pipes.
Internal plumbing leaks, e.g. below baths or broken mastic seals around showers.
Flooding.
High local water table.

Seeking professional help

Find the source before you pay for a remedy.

Most damp problems have more than one cause, and the cheap causes are as common as the expensive ones. A blocked gutter and a raised flower bed together will produce a wall that looks like a textbook case of ‘rising damp’.

Ask for a JPS 2022-compliant survey

Where the cause is not obvious, contact a specialist building surveyor and ask for an investigation compliant with the Joint Position Statement on investigating moisture in traditional buildings (JPS 2022).

Independent advice, not a sales visit

A free damp inspection offered by a company that also sells the treatment is a quotation, not a diagnosis. Independent means the person inspecting has nothing to gain from the remedy.

A diagnosis names the source

A report that stops at penetrating damp, condensation or rising damp has described the route the water took. It should go on to say where the water is coming from and what to do about it.

Before you call

What to gather about your own damp problem.

The more of this you have to hand, the quicker the cause can be narrowed down — and the less of the investigation has to be paid for.

Photograph the affected area, and the wider wall, floor or ceiling around it, inside and out.

Note when it appears and whether it changes with the weather, the heating or how the room is used.

Check the outside of the building while it is raining, particularly gutters, downpipes and gullies.

Gather any previous reports, guarantees, quotations or records of repairs already carried out.

Common questions

Damp at a glance.

What is damp in buildings?

Damp can be described as excess moisture that should not be there. If any part of your home is not dry to the touch, has mould growth or has a musty smell, you should investigate. Damp comes from many sources and takes different forms.

What is rising damp?

‘Rising damp’ is a term often misused to describe moisture that has moved vertically upwards from the ground below by capillary action or suction, like a sponge sitting in a puddle slowly soaking up water through the tiny holes inside it. It is often misdiagnosed — a typical misdiagnosis would be that ‘rising damp’ is the cause of your problem and that your home needs a new damp-proof course. It is not a conclusion, because it does not identify the source of the excess moisture, and failure of an original damp-proof course is extremely rare.

Are penetrating damp, condensation and rising damp causes of damp?

No. Penetrating damp, ‘rising damp’ and condensation are not causes of damp but are different ways moisture moves through, or onto, parts of a building. To solve a damp problem, you first need to find where the moisture is coming from.

What causes damp in a house?

Common causes include leaking or blocked gutters and rainwater pipes, ill-fitting doors and windows, roofing defects such as poor flashings and broken tiles, open chimney pots, poor external pointing, cracked render, raised ground levels next to walls, excess rubble under suspended ground floors, failed underground drainage, leaking water main supply pipes, bridged cavity walls, blocked low-level through-wall vents, broken sealant or mortar around windows and doors, internal plumbing leaks, flooding and a high local water table.

Can I investigate a damp problem myself?

Yes, up to a point. Anyone can investigate and look for problems — for example, you could go outside in the rain and see whether your gutters are overflowing. If something doesn’t look right, it usually isn’t right. Finding the cause can be complex, though, so where it matters it is best to contact a specialist building surveyor and ask for a Joint Position Statement (JPS 2022)-compliant survey.

Do I need a new damp-proof course?

Rarely. Failure of an original damp-proof course is extremely rare, and a new damp-proof course is one of the most commonly prescribed remedies for a problem that was never diagnosed. Find the source of the moisture first, and seek independent advice from someone who does not sell the treatment.

Independent by design

We diagnose the damp. We do not sell the cure.

We are consultants, not contractors, so we have nothing to gain from recommending a damp-proof course, a re-render or a treatment. We measure moisture, temperature and airflow together to establish where the water is actually coming from.

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