Lasting damp and mould repairs start with a diagnosis of the cause: condensation, penetrating damp, rising damp, leaks or cold bridging. Treating the mould alone rarely stops it returning. Fix the moisture source, the ventilation and the cold surfaces, and record readings that show the cause was dealt with.
Damp and mould stays fixed only when the cause is fixed. The usual causes are condensation, penetrating damp, rising damp, leaks and cold bridging, and many homes have more than one at once. A good repair diagnoses the cause with readings, fixes it, and then treats the mould and makes good.
What causes damp and mould in homes?
- Condensation: moist air meets a cold surface and turns to water. It shows up in kitchens, bathrooms and bedrooms, in the corners of external walls, behind furniture and around windows.
- Penetrating damp: water gets in through the building fabric, for example from defective roofs, blocked or leaking gutters and downpipes, failed pointing or render, or poor window seals. Patches are often local and worse after rain.
- Rising damp: ground moisture rises through the wall where there is no effective damp-proof course, or where it is bridged by raised ground levels or render. It is often confused with condensation or penetrating damp at low level, so confirm it before specifying a remedy.
- Leaks: plumbing, waste and heating pipes, or water from the flat above. These tend to appear suddenly and in one place.
- Cold bridging: heat escapes through a weak point in the insulation, such as a lintel, a concrete frame, a wall-to-ceiling junction or a gap in loft insulation at the eaves. Condensation then forms on the cold spot.
How do you diagnose the cause with readings?
Survey the whole home, not only the room the tenant reported. A sound diagnosis usually includes:
- Humidity and air temperature in each room, to show how much moisture the home is holding.
- Surface temperatures at the affected areas, taken with an infrared thermometer or thermal camera. A surface close to the dew point will attract condensation.
- Moisture readings on a grid across the affected wall, mapped and photographed. Resistance meters are affected by salts and some materials, so treat their readings as comparative and take samples where the cause is still unclear.
- An external inspection of the roof, gutters, downpipes, pointing, render, ground levels and air bricks.
- A ventilation check: do the extract fans run and actually extract, are trickle vents present and open, and can air move between rooms?
- A heating check: can the system heat every room, and are the controls working?
Record each reading with its location, date and time. The same record supports your Awaab's Law investigation in England. See Awaab's Law explained.
Which ventilation fixes work?
- Humidity-controlled extract fans in kitchens and bathrooms switch on as humidity rises and run on afterwards. Check the duct run and the outlet, since a long or crushed duct cuts performance.
- dMEV (decentralised mechanical extract ventilation) runs continuously at low speed in wet rooms and boosts when humidity rises. It suits homes where tenants switch off noisy intermittent fans.
- PIV (positive input ventilation) supplies filtered air into the home, usually from the loft, to dilute moist air. It is often used where condensation affects several rooms. It does not cure penetrating damp or leaks.
- Trickle vents give background ventilation through the windows. They are often closed, painted over or missing after window replacement, and can be retrofitted.
Undercut internal doors where needed so that air can reach the extract points.
How do insulation and cold spots affect mould?
Cold surfaces attract condensation, so insulation gaps often show up as mould. Common problems are missing or displaced loft insulation at the eaves, uninsulated solid walls, and cold bridges at lintels, reveals and floor slabs.
Retrofit can help or harm. Insulation without a matching ventilation upgrade can raise humidity, and poor detailing around windows can create new cold bridges. Government-backed retrofit uses the whole-house approach in PAS 2035:2023 for this reason. See whole-house retrofit and loft and cavity insulation.
Why does mould come back?
- The mould was washed and repainted, but the moisture source was not traced.
- A fan was fitted but is switched off, poorly ducted or too small for the room.
- A roof or gutter was repaired, but the wall was not given time to dry before making good.
- A cold bridge or insulation gap was not addressed.
- The fix does not work for how the home is used, for example where there is nowhere to dry clothes.
Book a follow-up visit with fresh readings so you can show the fix has worked.
What do the Ombudsman and the Decent Homes Standard expect?
- Housing Ombudsman: its spotlight report It's not lifestyle (October 2021) recommended a "zero-tolerance approach" to damp and mould, and its follow-up report came in February 2023. The title reflects its message that landlords should not default to blaming tenants' lifestyles.
- Decent Homes Standard (England): the reformed standard adds criterion E, under which homes must be free from damp and mould. All social and private rented homes must meet the reformed standard by 2035 at the latest. See the Decent Homes Standard.
- Wales: damp and mould is one of the 29 fitness matters in the Renting Homes (Fitness for Human Habitation) (Wales) Regulations 2022. See Wales standards.
- Scotland: the Investigation and Commencement of Repair (Scotland) Regulations 2026 set timescales for investigating damp and mould. See Scotland standards.
Check the current legislation and guidance for the nation your homes are in, or take advice for your own case.
Do monitoring sensors help?
Humidity and temperature sensors show conditions over weeks rather than on the day of a visit. They can flag homes at risk and confirm whether a fix has worked. Before installing them, agree how alerts are triaged and recorded, who responds, how tenants' data is handled and who maintains the devices.
What does damp and mould work cost?
These figures are context only. Actual costs depend on the cause, the number of rooms and how much making good is needed.
| Item | Figure | Source and year |
|---|---|---|
| Category 1 damp and mould remediation, average per dwelling | £985 | BRE 2023 data in the Awaab's Law final impact assessment (June 2025); VAT basis not stated |
| Mould wash and treatment, per room | £200–£400 | Checkatrade, May 2024, ex VAT |
| Mould wash and treatment, whole house | £700–£3,000 | Checkatrade, May 2024, ex VAT |
| New extractor fan | £250–£350 | Checkatrade, June 2026, ex VAT |
| PIV unit, supply and fit | £763–£1,750 (average £900) | Checkatrade, May 2024 |
Fabric causes such as roofs, gutters or insulation cost extra. See guide prices.
How we help
We survey for the cause, record readings and photos, and carry out damp and mould remediation together with the roofing, rainwater, ventilation and insulation work that removes the source. Where a measure needs certified people, we confirm in writing, before appointment, who will carry out each measure and what certification they hold. Request a quote for a single home or a programme.
Common questions
Is a mould wash enough on its own?
Usually not. A wash and stain-block repaint removes the visible growth but leaves the moisture source in place, so the mould tends to return unless the cause is also fixed.
Which ventilation option suits a whole-house condensation problem?
Positive input ventilation is often considered where condensation affects several rooms, while humidity-controlled extract or dMEV deals with moisture at source in kitchens and bathrooms. The right choice depends on the survey findings.
Does the reformed Decent Homes Standard cover damp and mould?
Yes. New criterion E requires homes to be free from damp and mould. All social and private rented homes must meet the reformed standard by 2035 at the latest.
Should sensor alerts be treated as reports of damp and mould?
Agree that in your policy before installing sensors. Decide who reviews alerts, how quickly, and how each one is recorded, so the data leads to action rather than sitting unread.
Sources
- Housing Ombudsman spotlight reports, including 'It's not lifestyle' (2021) and its 2023 follow-up
- Reformed Decent Homes Standard: government response (MHCLG)
- Hazards in Social Housing (Prescribed Requirements) (England) Regulations 2025
- Awaab's Law final impact assessment (2025)
- Investigation and Commencement of Repair (Scotland) Regulations 2026
- Renting Homes (Fitness for Human Habitation) (Wales) Regulations 2022
Checked 31 October 2026. This guide summarises the rules for planning purposes and is not legal advice; check the current legislation or take advice for your own case.
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