Mould Behind Furniture and in Closets on Outside Walls

If your windows stream every morning, check behind the wardrobe on the outside wall. The same moist air that wets the glass also finds the other cold surfaces in the room, and the ones hidden behind furniture never get a chance to dry.

Why it happens there

• Outside walls are colder than inside walls in winter, and the corners and spots near the window head are colder still. Building Science Corporation’s BSD-012 names exterior corners, wall/ceiling junctions, and poorly insulated window headers as the usual mould locations.
• A wardrobe or headboard pushed tight to that wall blocks the room’s warm air, so the wall surface behind it gets even colder.
• Moist air still seeps into the gap, the surface stays damp, and mould gets the steady moisture it needs. US EPA’s brief mould guide makes the same point: the key to mould control is moisture control.

What to do

1. Leave a gap. UK housing-association condensation guidance recommends pulling wardrobes, beds, and sofas about 10 cm off outside walls. Even a smaller gap lets air move.
2. Lift it. Furniture on legs or blocks lets air circulate underneath as well as behind.
3. Open closets. Prop wardrobe and closet doors open for part of each day, don’t pack them tight, and never put damp clothes away.
4. Bring humidity down. The EPA advises keeping indoor relative humidity below 60% (ideally 30–50%), and in cold Canadian winters you’ll often need to be at the low end to protect the walls. A hygrometer placed in the bedroom tells you which side of that line you’re on.
5. Exhaust at the source. Run bathroom and kitchen fans during and after showers and cooking, and avoid drying laundry in the bedroom.
6. Clean small patches promptly. The EPA says to clean mould off hard surfaces and dry them completely. Large areas, or mould that keeps returning, point to a wall that needs a professional look at insulation or air leaks.

Sources: US EPA, A Brief Guide to Mold, Moisture and Your Home; Platform Housing Group, Condensation mould on walls, in wardrobes and on furniture; Building Science Corporation BSD-012.

Originally published at https://dry-glass-notes.surge.sh/articles/mould-behind-furniture-closets-outside-walls.html (AI-assisted, sources cited). If this helped, zaps go to hollisvarrow3753@coinos.io.