SiLOSSiLOS

Moss on the roof and the zinc strip

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1The short version

Moss doesn't know it's on a roof. All it knows is damp and shade, and the north slope of your house offers both better than most of the forest floor does. It traps debris that keeps the surface wet longer, which speeds up rot on wood roofs and lifts shingles on any roof, letting water sneak under the edge. Algae streaks are its cousin doing the same thing on brighter, more open roofs. Metal roofs almost never grow either, because the surface is too slippery for moss to root.

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2The zinc strip, honestly

Zinc and copper strips are a real product and a mostly-myth fix. Rainwater does carry a little metal down the roof and moss won't grow directly under the strip, but everywhere else keeps growing exactly as before, the strips can cause leaks if nailed on wrong, and the metal runoff is bad for fish downstream. University pest-management guidance is blunt that installing zinc or copper strip products is not an effective way to eliminate moss.

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3What actually works

First, sunlight: trim back branches shading the roof, since moss won't grow where it's dry and bright. Second, remove what's there with a stiff bristle brush or broom, working gently on asphalt so you don't strip the granule coating. Third, keep the roof swept clear of leaves and needles before rain, since debris is what lets moss get a foothold in the first place.

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4What goes wrong

Pressure washing a roof is the single most common overcorrection: it's fine for a patio or a sidewalk and a bad idea for shingles, which lose their protective granules under that much force. Ignoring the moss isn't free either; it can shorten a roof's working life and turn a moss job into a moss-plus-water-damage job.

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5The first hour

Clear the roof of loose debris first, sweeping or blowing it off so you're not just grinding dirt into the shingles. Then start at the top of the mossy patch and scrape or brush downhill, dropping the dead moss into a tarp on the ground instead of the gutter. Wet moss is slick moss, so this is a dry-day job, ideally with a second person holding the ladder.

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