Q: What's the best method to remove moss from asphalt shingles and prevent
re-growth?
A: Moss and lichen are both highly sensitive to zinc, and this Achilles Heel
is the key to a fix. Up near the peak of your roof, install a 1-inch strip
of galvanized steel flashing or pure zinc strip underneath the top course of
shingles. Allow 1-inch of this metal to remain exposed to the weather. Be
sure you actually get hot-dipped galvanized steel for this job and not the
more common aluminum flashing sold everywhere. As rain and melt water
trickles down over the metal it dissolves small amounts of zinc that kills
the current moss growth and prevent a reoccurrence. Sometimes it's necessary
to remove existing lichen growth with a gentle pressure washing, but the
zinc always prevents re-growth.
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