Mould behind the wardrobe: why it grows and what to do now

Why does a wardrobe make the wall so cold?

Think of the wardrobe as a thick blanket hung on the wrong side. The room's warmth normally reaches the wall by moving air and by radiation from the radiator and the people in the room. Put a big box of clothes in front of it and both are blocked. The patch of wall behind loses heat to the outside just as fast, but gets far less heat from the room, so its surface temperature drops.

The air in the gap barely moves either. Damp air drifts in, cools against the wall and stays. That is why the mould often appears as a neat rectangle the shape of the wardrobe, darkest at the bottom corners and at the edge where the outside wall meets another outside wall or the floor.

The same happens behind a headboard, a cot, a chest of drawers or a sofa on an outside wall. The bigger and closer the furniture, the colder the wall behind it.

I've just found it. What should I do first?

1. Empty the wardrobe and pull it away from the wall. Do it with the window open.
2. Put on a mask (FFP2 or FFP3), gloves and eye protection before touching the mould.
3. Wipe, do not brush. Use a fungicidal wash on the wall as the label directs, with a damp cloth. Never scrape or vacuum dry mould, as that spreads spores.
4. Check the back of the wardrobe. Hardboard and MDF back panels soak up moisture. A light surface growth can be cleaned. A panel that is stained through, soft or smells musty is better replaced.
5. Take photos and note the date. If you rent, send them to your landlord in writing.

Bleach is not a fix. It lightens the stain but does not reach mould in the plaster, and the patch returns as soon as the wall gets wet again. A large patch, or one in a child's room or in a house with someone with asthma, is worth handing to a professional. My condensation and mould service includes safe removal with a mask.

Can I save clothes and shoes with mould on them?

Most of the time, yes. Washable clothes can usually be rescued by washing at the hottest temperature the label allows, ideally twice, and drying them outside or in a tumble dryer rather than on a radiator indoors. Leather shoes, bags and belts can often be cleaned with a damp cloth outdoors and left to dry naturally, away from direct heat.

Items that still smell musty after washing, or delicate items that cannot be washed, are better professionally cleaned or let go. Do not put the clothes back until the wall and the wardrobe are dry, or the smell comes straight back.

Where should the wardrobe go now?

On an internal wall if you can. Internal walls have a heated room on the other side and stay close to room temperature, so mould rarely grows behind furniture on them.

If the only space is the outside wall:

• leave a gap of 5 to 10cm between the back of the wardrobe and the wall;
• raise it on legs or a plinth with a gap so air can move under and behind it;
• avoid packing it so tightly that air cannot move between the clothes;
• open the doors for a few minutes each morning when you air the room;
• keep a hygrometer in the room and aim for 40% to 60% humidity.

A gap helps a lot, but it does not warm the wall. On a cold solid brick wall the mould can return to the gap itself, just more slowly.

What about fitted wardrobes on an outside wall?

Fitted wardrobes are harder, because they are built tight to the wall, often floor to ceiling, with no gap at all. In 1930s houses they are commonly fitted along an outside wall or into the space beside a chimney breast, and those are often the coldest walls in the room.

Options, from simplest:

• drill or fit discreet vents at the top and bottom of the doors or the plinth so air moves through;
• fit a back panel with a ventilated gap behind it, if the carcass can be adjusted;
• warm the wall itself before the wardrobe goes back, with a thin cork coating or full internal wall insulation.

If you are about to have fitted wardrobes built on an outside wall, that is the moment to insulate it. It is far easier with the room empty than after the joiner has finished.

Can I insulate just the patch behind the wardrobe?

I would not. If you insulate only part of a cold wall, the cold simply moves to the edge of the insulation, where the warm insulated section meets the cold bare brick. That line can become the new place where condensation and mould appear.

The wall needs treating as a whole, from corner to corner and floor to ceiling, with the window reveals and junctions detailed properly. That is also where moisture modelling matters: I check how the new build-up will handle water vapour before choosing a system, so the brickwork can still dry out. My guide to thermal plasterboard vs wood fibre vs PIR compares the options.

How much warmer would the wall be with insulation?

A lot warmer, and that is what stops the mould. In my 1930s bedroom case study, the calculated inside surface temperature of a 225mm solid brick wall rose from about 14.5°C to about 18.4°C on a 0°C day with the room at 20°C, after 40mm of wood fibre and lime plaster. A wardrobe in front of a wall at 18.4°C has much less chance of pushing the surface down into the mould zone.

For the physics behind these numbers, read condensation on bedroom walls.

When should I get the wall looked at?

When the mould comes back to the same place after you have cleaned it, moved the wardrobe and kept the room aired. That pattern means the wall is too cold, and the furniture was just the final push. It is also worth checking that the patch is not water getting in from outside, such as a leaking gutter above that part of the wall.

On a free home visit I check the outside, measure the wall and the room, and explain what is causing it. If the wall needs insulating, internal wall insulation starts from about £2,300 per wall, with a written quotation. Book a visit or call me on 07763 789272.

Common questions