Can Mold Grow in Winter? Utah Homes Explained

Where winter mold comes from

• Window condensation — warm, humid air hitting cold glass. See window condensation mold.
• Attic condensation and frost — warm air leaking into a cold attic, especially from bath fans that vent into the attic. See mold in your attic.
• Ice dams — melting snow backs up under shingles and leaks into walls and ceilings. See ice dam prevention.
• Frozen and burst pipes — sudden water inside walls. See frozen pipe guide.
• Closed-up houses — showers, cooking, laundry, and humidifiers raise indoor humidity with nowhere to go.
• Cold exterior walls and closets — corners and closets on outside walls stay cold enough for condensation behind furniture and stored items.

Prevention checklist

1. Keep indoor humidity moderate in winter — a $15 hygrometer helps.
2. Run bath fans during and after showers; make sure they vent outside, not into the attic.
3. Use the kitchen hood when cooking.
4. Turn humidifiers down when windows sweat.
5. Pull furniture a few inches off exterior walls.
6. Keep closet doors on exterior walls cracked open.
7. Check the attic after big storms for frost, wet insulation, or stains.
8. Know your main water shut-off — how to find it.

Signs to watch for

• Musty smell — tracking a musty smell
• Black spotting on window sills, closet walls, or ceiling corners
• Peeling paint or stains on ceilings below the attic
• Frost on the underside of the roof deck