How do I know if I have rising damp or condensation?

Condensation: black mould (Cladosporium) in corners and on cold surfaces, worse in winter, improves in summer. Rising damp: tide mark at 0.5–1m height on walls, salting (white crystalline deposits), peeling wallpaper at low level. Rising damp is much less common than condensation in Welsh homes.

How much does damp proofing cost in Wales?

Chemical DPC injection (genuine rising damp): £500–2,000 depending on property size. Basement tanking (cavity drain membrane): £3,000–10,000+. Replastering after damp treatment: £800–3,000. Always get an independent survey before committing to treatment.

Is condensation damp covered by buildings insurance?

Rarely, insurance typically covers sudden and unforeseen events (burst pipes, storm damage) not gradual issues like condensation. Some policies have damp exclusions. Check your policy wording before claiming.

Damp in Welsh homes: damp proofing vs ventilation

Damp is the most misdiagnosed and most over-sold building problem in Wales. This guide helps you understand what type of damp you have, and whether you need expensive damp proofing treatment or simply better ventilation.

The three types of damp

1. Condensation damp, the most common. Warm, moist air (from cooking, breathing, bathing) meets a cold surface and deposits moisture. Appears as black mould (Cladosporium), typically in corners, on north-facing walls, around window reveals, and in poorly ventilated rooms.

2. Penetrating damp, water entering through failed external elements: leaking roofs, cracked render, failed pointing, faulty guttering, or poor window seals. Appears as wet patches that worsen during and after rain.

3. Rising damp, capillary action drawing ground moisture up through walls. Much rarer than commonly claimed. A genuine DPC (damp proof course) failure typically presents as a tide mark at low level (0.5–1m), affecting the wall but not the floor. Often over-diagnosed.

Why Welsh homes are more vulnerable

Wales has:

Among the highest rainfall in the UK (up to 3,000mm/year in Snowdonia, 1,200–1,600mm in the valleys)
A large stock of pre-1919 solid-wall housing (no cavity wall, no original DPC in many)
Abundant valley housing in narrow, north-facing plots with limited sunlight
Older housing with lime plaster replaced by modern gypsum, which is less breathable

This combination makes condensation and penetrating damp significantly more common in Wales than in drier UK regions.

Condensation: the most common type

If you have black mould that's worst in winter, in corners and on colder surfaces, and which improves in summer, you almost certainly have condensation, not rising damp.

Treatment is behavioural and ventilation-based:

Increase ventilation: trickle vents in windows, extractor fans in kitchen and bathroom (min. 15 litres/second in bathrooms, 30 litres/second in kitchens)
Reduce internal moisture: dry clothes outside or in a tumble dryer, cover cooking pans, avoid drying clothes indoors
Heat rooms consistently: cold rooms condensate more, a small amount of background heating prevents cold-wall condensation
Apply anti-condensation paint or thermal liner to cold wall surfaces
MVHR (mechanical ventilation with heat recovery) is the premium long-term solution for badly affected homes

You do not need a damp proofing company for condensation. Chemical DPC injection does nothing for condensation damp.

When damp proofing is actually needed

Genuine damp proofing treatments are needed for:

Penetrating damp, the correct fix is to identify and repair the external source first. This might be a roofer (slipped slates), a builder (cracked render, repointing), a plumber (leaking gutters), or a window fitter (failed seals). Once the external source is fixed, allow the wall to dry (6–12 months) before replastering.

Rising damp, if a damp survey confirms genuine rising damp (requires a specialist damp meter reading, not just a visual inspection), a chemical DPC injection can be effective. However, this is far less common than damp companies claim.

Basement tanking, for below-ground spaces, cavity drain membrane or tanking systems are appropriate.

Damp survey scams to avoid

The damp proofing industry has a well-documented problem with mis-selling. Common patterns:

Free surveys that always find rising damp, companies offering free surveys have a financial incentive to find problems requiring treatment. An independent surveyor (RICS qualified) will give an honest assessment.

Invasive diagnosis without proper moisture mapping, a legitimate damp assessment uses a calibrated moisture meter on multiple readings, cross-referenced with external weather data. A visual inspection that immediately recommends £2,000+ of treatment is not a survey.

Selling DPC injection for condensation, chemical injection does nothing for condensation damp. If a company diagnoses "rising damp" in an upper-floor flat or in a room with obvious condensation patterns (corner mould, cold surfaces), they're selling you the wrong treatment.

Always get a second opinion, particularly for alleged rising damp. A RICS-qualified surveyor or a Property Care Association (PCA) member who doesn't do their own treatment work will give a more reliable assessment than a company who sells the treatment.

Damp in Welsh homes: damp proofing vs ventilation: what you actually need