Get the Moss Off Your Roof

Moss is the single most damaging thing growing on a mid-Island roof. Algae stains. Lichen marks. Moss actually gets under the roofing and lifts it, and once it has done that, water follows.

Here is what is happening up there. Moss anchors with rhizoids — fine root-like threads that push into every seam, crack and gap they can find. On an asphalt roof that means the leading edge of each shingle. As the mat thickens it wedges the shingle edge upward, breaking the seal that holds the course flat. Now there is a gap. Wind-driven rain, which we get plenty of here, goes in through the gap instead of running over the top.

And moss holds water. A saturated moss mat keeps a permanent damp patch against the shingle and the deck beneath it. Roofing is designed to shed water quickly, not to stay wet, and a surface that never dries out ages far faster than one that does. On cedar shakes the effect is worse again — trapped moisture is exactly how shakes rot.

Why it happens so fast here

Shade and moisture, which describes most of Vancouver Island between October and April. Any roof with fir or cedar overhanging it, any north-facing slope, any valley where needles collect: those are the spots where moss starts. It rarely takes over the whole roof at once. It begins as small dark clumps along the shingle edges and in the valleys, and it spreads outward season by season.

Left alone across several wet winters the mat thickens, the lifted edges multiply, granules wash off with every rain, and eventually you are dealing with leaks and replacement rather than cleaning.

How we remove it

Removal is deliberately gentle and deliberately slow. We work from the top of the slope downward so we are never dislodging debris onto a section we have already cleared, and we take the moss off with hand tools and soft brushing — no scraping across the grain of the shingle, no wire brushes, no high-pressure wand.

That last point matters more than anything else on this page. High pressure will absolutely remove moss. It will also remove the mineral granules that protect the asphalt from UV, and those granules are the shingle's lifespan. Roofs blasted clean look great for a season and then age extremely quickly. Every roofing manufacturer says the same thing about it.

Thick, well-established mats sometimes cannot be fully removed in one pass without damaging the roof underneath. When that is the case we take off what comes away safely, treat the remainder, and let the dead residue weather off over the following months. That is the honest answer, and it is better than the alternative.

Treatment and regrowth

After the physical removal we apply a moss treatment across the roof. This kills off the spores and fragments left behind in seams and under the shingle edges — the pieces you cannot see and cannot pick out, which are exactly where regrowth starts.

Nothing is permanent. Moss spores are in the air constantly on this coast, and a shaded roof under trees will start again. What treatment does is reset the clock and slow the process down, and the difference between a treated and untreated roof over a few years is substantial.

You can help. Trimming back branches that overhang the roof cuts both the shade and the constant drop of needles and organic debris that gives moss something to root into. Keeping the gutters clear stops debris backing up onto the lower course. Neither is glamorous and both make a real difference.

Timing it right

Late spring through early autumn is the practical window, when there are enough dry days to work safely and the treatment can do its job. Removal in the depths of a wet winter is difficult and a lot less effective.

The best time to book is the season before you think you need it. Moss you can see clearly from the driveway has usually been up there a while.

Booking it

Gutters get done at the same time on most moss jobs — everything we take off the roof has to end up somewhere, and that somewhere is your gutters. We will always tell you honestly what shape your roof is in. If it is near the end of its life, cleaning it is not the right spend and we will say so.

We cover Nanaimo, Lantzville, Nanoose Bay, Cedar, Parksville, Qualicum Beach, Ladysmith, Chemainus, Errington and Coombs, Monday to Friday, 9:00 AM to 5:00 PM. Quotes are free.