Why is there mould behind my wardrobe or sofa, and what should I do about it?

Mould behind a wardrobe or sofa is usually a sign of condensation. Warm, moist air from everyday living drifts into the still, cool pocket behind the furniture, meets a cold wall and turns back into water. Government guidance names the low points on walls behind sofas and wardrobes as a typical spot, and calls condensation the most common form of damp. The answer is to clean the mould safely, then deal with why that wall is staying cold and wet, rather than just wiping it away.

Why mould picks the wall behind your furniture

Condensation happens when water vapour in the air cools and turns into tiny droplets on the coldest surfaces in a room. Cooking, showering, drying washing and simply living in a home all add moisture to the air.

A big piece of furniture pushed tight against a wall stops warm air reaching it and stops air moving behind it. That patch of wall stays colder and damper than the rest of the room, which is exactly what mould likes. Outside walls are the usual trouble spots: RICS notes that mould from condensation typically forms around windows, on external walls and on ceilings close to external walls.

Sometimes you smell mould before you see it. Government guidance says a mouldy smell without visible mould may mean there is mould behind a surface, including behind furniture. A musty wardrobe is worth pulling out and checking.

It is not always just condensation

Condensation is the most common cause, but not the only one. Water can get in from outside through defects in walls, roofs, windows or floors, or from leaking pipes and overflows inside. There can be more than one cause at once, and other kinds of damp can make condensation worse. RICS describes a living room where water coming up through a solid floor raised humidity and led to condensation on the walls.

Signs that something more may be going on include:

• the patch stays damp even after the furniture has been moved away and the room aired
• staining, peeling wallpaper or defective plaster on the same wall
• the mould appeared from a particular time, which RICS says may mean something has changed, such as an escape of water or more people living in the home
• gutters or downpipes on that side of the house overflowing when it rains

How to clean it safely

Before you clean, take photos of the mould and, if you can, draw round its edge. Government guidance suggests this record can help work out where the moisture is coming from and plan what to do.

For small patches on hard surfaces such as painted plaster:

• use a mould and mildew cleaning product rather than bleach, and follow the product instructions
• wear gloves, a mask and goggles
• keep the room door shut so spores do not spread to the rest of the house, but open the window during and after cleaning
• leave the surface to dry completely
• wash or throw away the cloth or sponge, and bag up anything you remove

Larger areas of mould, such as a substantial part of a whole wall or ceiling, should only be tackled by qualified professionals.

The back of a sofa or the inside of a wardrobe is harder. Government guidance says absorbent materials such as soft furnishings may have to be thrown away if they become mouldy, because it may be difficult or impossible to remove the mould completely. Check clothes, bags and shoes stored against the back wall too.

Take care when disturbing mould. Pulling off wallpaper or lifting carpet can release a lot of spores. If the area is large or you are unsure, get advice from a trained professional first.

Mould and your health

Government guidance says damp and mould primarily affect the airways and lungs, but they can also affect the eyes and skin. It says everyone is vulnerable to the health impacts of damp and mould, but people with certain health conditions, children and older adults are at greater risk of more severe health impacts.

If you are concerned about any symptoms, speak to a healthcare professional. For renters, the same guidance is clear that landlords should not wait for medical evidence before acting on damp and mould.

Stopping it coming back

Cleaning deals with what you can see, but government guidance warns that simply removing surface mould will not stop damp and mould reappearing. These everyday steps help keep condensation down:

• leave a gap between furniture and outside walls so air can move behind it
• use extractor fans when cooking, bathing or showering, and keep kitchen and bathroom doors closed
• cover pans when cooking
• dry washing outdoors where you can, rather than over radiators
• open windows regularly: RICS says about 5 minutes for every hour you are in a room is enough, or you can use trickle vents or the secure window latch
• do not block air vents in bedrooms and cupboards
• keep the home heated: RICS suggests ideally between 18C and 21C

These habits help, but they cannot make up for a home that is cold, poorly ventilated or letting water in. Government guidance says it is totally unreasonable to blame damp and mould on lifestyle choices, and that the fundamental cause will be building deficiencies, inadequate ventilation, inadequate heating or poor energy efficiency, not normal day-to-day living.

If money is tight and you can only afford to heat yourself rather than the house, RICS points out that not heating the home adequately can add to condensation, and that the home still needs ventilation.

If you rent your home

Tell your landlord or managing agent about the mould promptly, and share your photos. Government guidance says landlords are responsible for addressing damp and mould whatever type of damp it is, should find and tackle the underlying cause, and should inspect the home at least 6 weeks after remedial work to make sure the mould has not come back.

On the law that applies now, the Housing Act 2004 states that rented properties must be free from hazards at the most dangerous 'category 1' level, assessed using the Housing Health and Safety Rating System, and this includes mould and all types of dampness. RICS says tenants with concerns under this system can contact their local council's environmental health team, which can take action against landlords for non-compliance.

Wardrobes against cold outside walls: a Yorkshire and Lancashire habit

Many homes across Yorkshire and Lancashire are older stone terraces and back-to-backs with solid walls. The general advice applies just the same: a wardrobe, bed or sofa against an outside wall, and especially an exposed gable end, creates the kind of cold, still pocket where condensation settles. Leaving a gap and keeping air moving matters.

Older solid-wall homes need care when it comes to repairs. RICS warns that in older buildings with solid walls, damp-proofing measures may not be appropriate and may make damp worse, and that modern cement in mortar or render on older buildings can trap moisture in walls. It also says failure of an original damp-proof course is extremely rare, so be cautious if mould behind furniture is put down to that without a proper look at other causes.

Be wary of anyone who relies only on a damp meter, particularly on stone or brick walls. RICS explains that these meters are accurate in timber but can give high readings in other materials because of things other than moisture.

If your house has a suspended timber ground floor with low-level air vents in the outside walls, keep those vents clear. RICS describes a house where blocked vents and raised ground levels outside led to damp floor timbers and moisture in the air, creating condensation.

When to ask a surveyor

If the mould comes back after cleaning and airing, keeps spreading, appears alongside staining or wet plaster, or there is no obvious reason for it, it is sensible to ask an independent, suitably qualified surveyor to find the cause. RICS suggests a building surveyor with experience in building pathology, and advises asking for a Joint Position Statement 2022 (JPS22)-compliant inspection. It says this gives an unbiased opinion from someone without a commercial interest in selling you a product. Ask about their experience with older local buildings before you book.

This page gives general information, not legal or medical advice. For your own situation, use the organisations listed under "Where this comes from" at the foot of the page.