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I can smell damp but I can't see mould, what does that mean?

Damp, mould and your health

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Direct answer

A damp smell without visible mould often means hidden damp behind walls, under floors, or in the structure. Here is what to do.

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Direct answer

A damp, musty smell with no visible mould almost always means the mould is hidden: behind plasterboard, under floors, inside an air gap, or in the loft above your flat. It is not in your head, and it is not because you "don't open the windows enough." Your landlord still has a duty to find and fix the cause. Call us free on 0800 030 4669.

Key facts

  • The 2024 to 2025 English Housing Survey found about 5% of homes in England, around 1.4 million, had a problem with damp, most common in privately rented homes (10%). English Housing Survey 2024-25, GOV.UK
  • Official guidance from the UK Health Security Agency and the Department of Health and Social Care links damp and mould in homes in England to around 5,000 cases of asthma and 8,500 lower respiratory infections among children and adults. Health risks of damp and mould, GOV.UK

Why you can smell what you can't see

Mould releases tiny gases as it grows. That is what the smell is. Even a small patch behind a wall or under a floorboard can fill a whole room. Common hiding places:

  • Inside the cavity of an external wall, especially below a window.
  • Under the floor, in the gap between joists.
  • Behind kitchen and bathroom cabinets where pipes pass through.
  • In the loft above a top-floor flat.
  • Inside the boxing around a soil stack or pipe run.

Hidden mould often starts because of a small, slow leak from a pipe, gutter, or flat roof. The water never appears, but the timber and plaster behind the wall stay wet for months.

Your landlord's duty

Just because it is not visible does not mean it is not your landlord's problem. Under Section 11 of the Landlord and Tenant Act 1985, your landlord must keep the structure and water installations in repair, even where the fault is hidden. Under the Homes (Fitness for Human Habitation) Act 2018, the whole home must be fit to live in, see what is the Fitness for Human Habitation Act.

For social tenants, Awaab's Law treats damp and mould as a serious hazard whether or not it is visible. The landlord must investigate and fix it within set deadlines. See what is Awaab's Law in plain English.

What to do

  1. Describe the smell in writing: where, when, how strong, and how long it has been there.
  2. Note any patches of cold wall, peeling paint, or warped skirting.
  3. Take photos of those signs even if there is no visible mould.
  4. Ask in writing for a damp survey. Use that exact phrase. A damp survey looks behind the surface; a visual inspection does not.
  5. If you have a moisture meter on a phone or smart hub, log readings.
  6. Mention anyone in the home with chest problems, asthma, or allergies.

See how to report damp to your landlord for the language to use.

What a damp survey will look for

A proper damp survey checks:

  • Moisture in the wall plaster.
  • Hidden leaks from above, below or behind.
  • Failed pointing on external brickwork.
  • Faulty or missing damp-proof course.
  • Roof or gutter leaks affecting upper-floor flats.

Without one, your landlord cannot honestly say there is no problem.

Your health

Hidden mould can affect breathing the same way visible mould does. If anyone has been to the doctor about coughing, wheezing, or repeated chest infections, ask for a printed summary of the consultation, see health evidence in a disrepair claim.

How we can help

If a damp smell has been there for months, your landlord refuses a proper survey, and your home feels colder and stickier than it should, you may have a claim. Call us free on 0800 030 4669.

Free call: 0800 030 4669 | Start your claim

Sources

Last updated28 May 2026
Reading time3 min read
Listening time4 min listen

We review every guide at least twice a year and update it when the law changes. If you spot something out of date or wrong, email help@supportfortenants.co.uk.

By: Support for Tenants

Published:

~3 min read

Reviewed against current housing law for England and Wales as at 28 May 2026. Checked by our SRA-regulated panel solicitors. This is general information, not legal advice for your specific case. Any compensation figures or ranges shown are illustrative only and not guaranteed; every case is different.

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