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Excellent on timber shingles and tiles but not on a iron roof though, it creates a battery and the iron rusts. Funnily enough an unpainted galvanized iron roof resists moss pretty well as zinc is...

Bleach is pretty much instant, it's alkalinity and the chlorine destroy moss on contact. "quats" (like benzyl alkonium chloride) takes several months to work but does have some residual activity....