Where is that smell coming from?

That smell hits you when you come in from outside, or when you open a wardrobe that’s been shut for a while. It’s stale, earthy, and hard to shift. Most people open a window and hope for the best, but if it keeps coming back, something specific is producing it. Find out why your home smells musty and what each cause means for you below.

Common causes of a musty smell in your home

Musty smells almost always come down to moisture. It’s usually sitting somewhere you can’t see it, and the smell is your first signal that something’s off. The main culprits tend to be:

• Condensation that could be forming on cold external walls, inside wall cavities, or behind plasterboard.
• A failed damp-proof course (DPC), where rising damp travels upwards through brick and plaster from the ground.
• Blocked air bricks at the base of external walls, which stop the sub-floor void from ventilating and allow moisture to build up.
• Poor extraction in kitchens and bathrooms, where humid air has nowhere to go.

Why the smell can be hard to trace

The frustrating thing about musty smells is that your nose tells you something is wrong but can’t tell you where. Moisture doesn’t always leave a visible mark, especially in the early stages. Damp inside a wall cavity, condensation forming behind plasterboard, or mould growing in a sub-floor void can all produce a noticeable smell long before any physical signs appear on the surfaces you can see.

That’s where most people get stuck. They’ve checked the obvious spots, wiped down the bathroom, pulled the sofa away from the wall, and the smell is still there. Without knowing the actual moisture levels inside the building fabric, you’re guessing.

That’s when professional air quality testing and damp surveys are the only avenue left to pursue. Air quality testing picks up elevated mould spore counts even when there’s no visible growth, and a proper damp survey uses moisture meters and thermal imaging to find where water is sitting inside walls, floors, and ceilings. Experts like ICE Cleaning offer both services and can map out exactly where the moisture is coming from, which means any remediation work that follows is targeted at the actual source rather than the symptoms. That’s the difference between fixing the problem once and chasing the same smell every few months.

Mould you probably haven’t found yet

Mould doesn’t always show up somewhere obvious. People check the bathroom tiles or the window frames, assume everything looks fine, and leave it there. But mould will grow wherever the conditions suit it, and that’s often somewhere out of view.

Pull a large piece of furniture away from an external wall and take a proper look. Cold walls with little air movement are one of the most common spots for black or grey mould, and it can cover a significant area on the back of the wall without ever being visible from the front of the room. Even a small colony will produce enough spores to make the whole space smell musty.

What to do before you call anyone

If you’ve spotted mould or noticed obvious damp patches, there are a few things worth doing first.

Check your air bricks. In older properties, these sit near the base of external walls and are easy to miss. Make sure they’re not blocked by soil, debris or old paint. Also check that extractor fans in the kitchen and bathroom are working properly, and keep large furniture a few centimetres from external walls to let air circulate.

If the smell comes back after all of that, it usually points to something deeper. Rising damp, moisture in a wall cavity, or a structural issue won’t be fixed by ventilation alone. A professional damp survey will tell you what you’re actually dealing with.

Final takeaways

Musty smells don’t go away on their own. Something in the property is producing or trapping moisture, and until that source is addressed, the smell will return.

Work through the basics first: air bricks, ventilation, and anything hiding behind the furniture. If none of that fixes it, a proper assessment will save you a lot of guesswork and help you deal with the problem before it gets worse.