How should moss be removed from a roof?
Moss holds water against the roof surface. Left alone it lifts shingles, and the water it holds finds the gaps that lifting creates. Where a roof stays shaded and damp for months at a time, it is the most common reason an otherwise sound roof starts leaking early.
Our process on a sloped roof is four steps. We inspect the surface, the flashings and the penetrations. We remove loose moss with hand tools and blown air. We liquid-apply a moss treatment to the entire roof surface. We clean the gutters.
The reason for that order is granules. The mineral granules on a composition shingle are what stop ultraviolet light destroying the asphalt underneath, and a roof that has lost them ages fast. Anything that scrubs, scrapes or blasts moss off a roof takes granules with it, so we do not do it.
Three things to avoid if you are treating a roof yourself. A pressure washer strips granules and can break shingles outright. Bleach kills moss and is corrosive enough to discolour the roof and damage the planting underneath it. Zinc sulfate powder leaves the roof structure alone but is harmful to pets, wildlife and vegetation.
There is no warranty on moss cleaning, and that is not a small-print dodge. Moss is a product of the environment: shade, slope and how much debris lands on the roof all change over time, and none of them are things a roofer controls. What we can tell you is that after the first proper cleaning, most roofs need only the preventative treatment afterwards rather than another clean.
Preventing it is cheaper than treating it. Cut back branches overhanging the roof, keep leaves and sticks off the surface, and keep the gutters clear.
Pacific Pride Roofing will not force or scrape moss from the roof surface. Aggressive removal can strip protective granules and damage the shingles. Some roofs need more than one treatment; any further treatment is a separate visit, priced at a lower rate because it is a lighter visit, and we agree the price with you before we do it. After treatment, remaining moss typically loosens and weathers off naturally with wind and rain. That granule and shingle warning describes composition and asphalt shingle roofs, and a metal, tile, cedar, rubber or composite, or flat or low-slope roof takes a different method. We agree the method for your roof with you before we start.
