Our exterior paint keeps growing mould and mildew on the north side. How do we deal with this in Vancouver?

Mould and mildew growth on north-facing exterior walls is extremely common throughout Metro Vancouver. The combination of limited direct sunlight, persistent moisture, and our mild winter temperatures creates ideal conditions for biological growth. It's not necessarily a sign of paint failure, but it does need to be addressed properly.

The first step is cleaning the existing growth. A solution of one part household bleach to three parts water, applied with a garden sprayer and scrubbed with a soft brush, will kill surface mildew effectively. Let it sit for 15 to 20 minutes before rinsing thoroughly. For larger areas, a professional soft wash using a low-pressure sprayer with a commercial mildewcide solution is safer for the paint than high-pressure washing, which can damage siding and drive water behind the clapboards.

Once clean, assess whether the paint itself is still in good condition. If it's just surface mildew on intact paint, a thorough cleaning followed by a coat of mildew-resistant paint may be all you need. If the paint is failing, you'll want a full prep and repaint using a premium exterior paint with high mildewcide content. Some manufacturers offer products specifically formulated for Pacific Northwest conditions.

Long-term prevention involves reducing moisture retention on the affected wall. Trim back any trees or shrubs that block airflow and sunlight from reaching the wall. Ensure gutters and downspouts are directing water away from the foundation and not splashing back onto the siding. Check that the ground slopes away from the wall so water drains rather than pooling.

In some cases, improving attic ventilation or adding exhaust fans that vent properly to the exterior can reduce the moisture migrating through the wall from inside the home.

Consider scheduling an annual spring cleaning of the north-facing walls as part of your regular home maintenance routine to prevent buildup from becoming a larger problem.

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