What keeps bringing moss back to my Vancouver roof every winter?

Moss keeps coming back to your Vancouver roof because the conditions that caused it in the first place never went away. Removing moss without addressing the root causes is like bailing a boat without plugging the hole — it'll be back within a season or two.

Vancouver's climate is essentially a moss paradise. With 1,200mm+ of annual rainfall concentrated between October and March, extended periods of overcast skies, and mild temperatures that rarely dip low enough to kill organic growth, your roof stays damp for months at a time. Moss doesn't need much — just moisture, shade, and a surface to grip — and asphalt shingles give it exactly that.

The biggest culprits are shade and debris accumulation. Overhanging branches do double damage: they block sunlight that would otherwise dry your roof between rain events, and they drop leaves, needles, and organic debris that pile up in valleys and along ridgelines. That debris layer holds moisture against the shingles for days after a storm, giving moss spores the perfect germination environment. If you have cedar, fir, or hemlock trees near your roofline — extremely common in Metro Vancouver — this is almost certainly a major factor.

Your roof's pitch and orientation matter a lot too. North-facing slopes and low-pitch sections (common on Vancouver Specials and older bungalows) stay wet far longer than steep south-facing surfaces. If moss is hitting one side of your roof harder than the other, this is usually why. Valleys and areas near dormers or skylights are also chronic problem zones because water pools and lingers there.

The long-term fix is a two-part approach. First, treat and remove existing moss properly — zinc or copper-based treatments are most effective, and many roofers apply zinc strips along the ridge so that every rainfall washes a small amount of zinc sulfate down the slope, which is toxic to moss. Second, address the conditions: trim branches back at least 2-3 metres from the roof edge, keep gutters and valleys clear of debris, and improve drainage so water moves off quickly.

On the product side, avoid pressure washing — it's tempting but it blasts away the granules on asphalt shingles, dramatically shortening their lifespan. A soft wash with a moss-killing solution, followed by gentle rinsing, is the right approach.

Typical professional moss treatment in Metro Vancouver runs $300–$700 for a standard house, depending on roof size, pitch, and accessibility. Full cleaning plus zinc strip installation adds another $200–$400. Some roofing companies offer annual maintenance programs, which can be worth it given how aggressively moss grows here.

This is one of those jobs that sits right on the DIY/pro line. If your roof is low-pitch and safely accessible, a homeowner can apply moss treatment products from a garden sprayer. But working on a wet, mossy Vancouver roof is genuinely dangerous — moss is slippery, and a fall from even a single-storey roof is serious. If there's any doubt about safe access, hire a professional.

You can find licensed roofing contractors serving Metro Vancouver in the Vancouver Construction Network directory — look for someone who specifically mentions moss treatment and soft washing in their services, as not all roofers offer it.