About this problem
Where it usually appears
What to look at
When to send photos
What a musty smell usually means
A musty or “damp” smell in a flat comes from moisture sitting somewhere — in the air, on a surface, or inside a small patch of mould that hasn’t spread far enough to be obviously visible yet. It’s the smell most people describe as earthy, stale or like a closed cupboard. On its own, the smell tells you moisture is present; it doesn’t tell you exactly where or how serious it is, which is why the next step is usually to find the strongest point of the smell rather than guess from memory.
Walking the flat room by room, with a note of where the smell gets stronger or weaker, is more useful than trying to place it from a doorway. A smell that’s roughly even everywhere often means the whole flat needs airing; one that sharpens near a particular wall or cupboard usually has a more specific source worth a closer look.
Smell but no visible mould — is it hidden?
This is the case that worries people most, and it deserves an honest answer: sometimes yes, sometimes no. A closed-up flat, a room with little airflow, or a cupboard that’s rarely opened can smell musty simply from trapped humid air, with nothing growing at all. But if the smell keeps coming back to the same spot — a corner, a wardrobe, behind a headboard — after you’ve aired the room properly, that pattern suggests a small patch of mould nearby, even if you haven’t spotted a mark yet. We can’t confirm hidden mould from a description alone, but a photo of the area, even without a visible mark, is a reasonable starting point.
Damp smell vs a drain smell
It’s worth ruling this out early, because it changes who you should talk to. A mould or damp smell is usually earthy and steady, strongest near a cold wall, window reveal or enclosed cupboard. A drain smell is usually sharper, comes and goes with water use, and is strongest near a sink, shower or toilet — that’s a job for a plumber, not for surface mould treatment. If you’re not sure which you’re smelling, note where it’s strongest and whether it changes when you run a tap; that’s often enough to tell the two apart.
The closed-up flat and holiday-let case
Flats left shut for a holiday, a long rental gap, or between tenants often develop a musty smell purely from stale, humid air with nowhere to go. In most of these cases, opening windows for real cross-ventilation over a day or two clears it completely. If the smell is still noticeable after that, or returns within a day or two of closing the flat again, it’s a sign there may be a small mould patch feeding it rather than just stale air.
Where to look
A few places worth checking with your nose and a torch:
- corners and walls that feel colder than the rest of the room
- inside wardrobes and cupboards, especially built-in ones on an outside wall
- behind furniture pushed close to an exterior wall
- under windows and around the frame
When a smell is worth photos and a look
If the smell is localised, doesn’t clear after proper airing, or you find even a small mark once you look closely, it’s worth sending a photo rather than waiting for it to spread. If the room is simply stuffy after being shut up, airing it is the sensible first step before anything else.
A photo shows the surface condition and helps suggest a sensible option — it cannot name the exact cause of damp or confirm hidden mould behind a wall; the cause is fairer to assess on site.
Related pages
With photos and a short note — contact. If you’ve already found a mark on the wall — mould removal. Not sure whether it’s worth calling anyone yet — see when to call a mould specialist.