Is it normal for exterior paint on the north side of my Vancouver home to grow algae and how do I clean it?

Yes, algae and mould growth on the north side of Vancouver homes is completely normal and expected. The combination of Metro Vancouver's marine climate, persistent moisture, and reduced sunlight creates ideal conditions for biological growth on north-facing exterior surfaces.

Why North-Facing Walls Develop Algae in Vancouver

North-facing walls receive minimal direct sunlight throughout the year, keeping surfaces damp longer after rain. With Metro Vancouver receiving over 1,200mm of annual rainfall and relative humidity regularly exceeding 80% from October through April, these shaded surfaces stay moist for extended periods. The lack of UV exposure means there's no natural sterilization effect that sun provides on south and west-facing walls.

Organic debris from trees — pollen, leaves, and dust — settles on these damp surfaces and provides nutrients for algae, mould, and mildew. Areas near ground level, under roof overhangs, or shaded by mature trees are particularly susceptible. The green or black discoloration you're seeing is typically a combination of algae, mould, and mildew rather than just one organism.

How to Clean Algae and Mould from Exterior Surfaces

Start with a pressure washer and mould-killing solution — this is the most effective approach for Metro Vancouver conditions. Mix a solution of 1 part bleach to 10 parts water, or use a commercial mould remover like Concrobium Mold Control or Wet & Forget. Apply the solution to dry surfaces and let it sit for 10-15 minutes before pressure washing.

For pressure washing technique, use a 25-degree nozzle tip and work from top to bottom, maintaining 12-18 inches distance from the surface. Too close or too narrow an angle can damage paint or drive water behind siding. Rent a pressure washer for $75-$150 per day in Metro Vancouver if you don't own one.

Alternative cleaning methods work for less severe growth. A garden sprayer with the bleach solution followed by scrubbing with a stiff brush can be effective on smaller areas. For homeowners concerned about bleach, oxygen bleach (sodium percarbonate) or specialized algae cleaners are gentler alternatives, though they require more scrubbing.

Prevention and Long-Term Solutions

Improve air circulation around affected areas by trimming vegetation away from the house and ensuring gutters drain properly. Standing water or poor drainage creates persistent moisture that feeds biological growth.

When it's time to repaint, choose mould-resistant exterior paint with built-in mildewcides. Premium paints like Benjamin Moore Aura Exterior, Sherwin-Williams Duration Exterior, or Dulux Lifemaster include mould inhibitors that significantly extend the time between cleanings. These paints cost $55-$90 per gallon but provide 2-3 years longer protection against biological growth.

Timing and Safety Considerations

Clean exterior surfaces during Metro Vancouver's dry season (May through September) when you can ensure 24-48 hours of dry weather after cleaning. This prevents immediate recontamination and allows surfaces to dry completely.

Always wear eye protection and avoid getting bleach solution on plants or landscaping — rinse vegetation thoroughly with water after cleaning. Never mix bleach with other cleaning products, and ensure adequate ventilation when working with chemical cleaners.

When to Call a Professional

Consider hiring a painting contractor if the growth covers large areas, if you're uncomfortable working at height, or if the algae has caused paint to peel or fail. Professional cleaning typically costs $300-$800 depending on house size and includes proper mould treatment and surface preparation for repainting if needed.

Most Metro Vancouver homeowners need to clean north-facing exterior surfaces every 1-2 years as part of regular home maintenance. It's a normal part of living in our marine climate, and staying ahead of it prevents more serious paint damage down the road.