How to Stop Window Condensation and Mould in a Vancouver Home

Every fall in Metro Vancouver, the same things show up: water streaming down the inside of windows in the morning, black spots in the corners of window frames and dark lines along the shower caulking. Our mild, wet winters keep the air outside damp, and closed-up homes trap the moisture from cooking, showers and drying laundry. The good news is that most of it is preventable with a few habits.

Why condensation happens

Warm indoor air holds moisture. When it touches a cold surface — a window, an outside wall, the corner of a closet — it cools and the moisture turns to water. Older single-pane and aluminum-frame windows get colder than modern double- or triple-pane windows, so they fog more. Condensation that sits on frames, sills and walls day after day is what lets mould grow.

Keep indoor humidity in check

Health Canada recommends keeping indoor humidity at no more than 50% in summer and 30 to 40% in winter. An inexpensive hygrometer tells you where you are. If you're above that range in winter:

• Run the bathroom fan during every shower and for a while after.
• Use the kitchen range hood when cooking — especially when boiling water.
• Dry laundry in a vented dryer rather than on a rack indoors, if you can.
• Open the blinds and curtains during the day so the glass warms up, and keep furniture a little away from outside walls so air can circulate.
• Run your HRV or ventilation system if you have one, and keep its filters clean.
• Consider a dehumidifier for basements and rooms that stay damp.

Daily window routine for wet months

1. Wipe condensation off the glass and sills each morning with a microfibre cloth or a small squeegee.
2. Keep window tracks clear — vacuum out debris so water can drain through the weep holes.
3. Air the room for a few minutes on drier days.

Cleaning small spots of mould

Health Canada's guidance is that you can clean small areas of mould yourself with dish soap and water — bleach isn't needed. Scrub, wipe the area clean and dry it thoroughly. Wear gloves, and ventilate the room while you work.

• Find and fix the cause — a leak, a blocked window track, a fan that doesn't vent outside — or the mould will come back.
• Replace mouldy caulking rather than trying to clean deep stains out of it.
• Clean and dry water-damaged areas quickly.

When to call a professional

For larger areas of mould, mould that keeps returning, a musty smell with no visible source, or any significant water damage, call a qualified professional to find the cause. If you rent, report it to your landlord in writing. A cleaning service like ours can keep surfaces, sills, tracks and bathrooms clean, but we're not a mould remediation company, and large or recurring mould needs the source fixed.

Our fall and winter cleaning checklist covers the rest of the wet-season jobs.