A: Moss and lichen on roofs are not uncommon and it doesn’t necessarily happen only in shady areas. I’ve seen quite thick growths in full-sun locations. This is especially true with lichen. The good news is that there are ways to remove the existing growths and prevent re-growth. Don’t cut down the tree if it’s healthy. Different products are sold for cleaning up roofs. I’ve used an oxygen-based stainer remover, a plastic bristle brush and a garden hose to remove moss. Some moss removers promise scrub-free results, but these take time to work.
To prevent moss re-growth, install strips of zinc underneath the top course of shingles. Building supply outlets everywhere sell it in rolls. It’s not cheap (about $1 per foot), but it does work. Small amounts of zinc will be dissolved as rain runs down the roof, preventing new moss and lichen from getting a foothold. It’s completely safe for people, pets and plants. You can see this effect happening accidentally around certain kinds of metal chimneys and rooftop vents that have zinc coatings. The moss-free effect is really quite striking.
To install zinc strips on roof you’re reshingling, nail down the zinc so an inch or two is exposed after the cap shingles get installed. If you’re adding zinc to an existing roof, you’ll find it easiest to pry up the bottom edge of the top-most coarse of shingles, slip the zinc underneath, fasten it with roofing nails every 3 or 4 feet, then place a blob of roofing tar from a caulking gun every 8 to 12 inches to hold the shingle down in the wind.