How do you prevent moss growth on a roof?

Why moss grows where it does

In North Georgia, moss shows up most on north and east facing slopes under hardwoods and pines. Those areas get little direct sun, dry slowly after rain and morning dew, and collect leaf litter and needles that hold moisture and give moss a foothold. Spores land everywhere, but they only establish where the surface stays damp long enough.

Change the conditions

• Let in sun and air: trim branches that shade the roof and keep limbs well clear of the surface. An arborist can thin the canopy without harming the tree.
• Remove debris: blow or brush leaves and needles off the roof, especially in valleys and behind chimneys, where they pile up.
• Keep gutters flowing: clogged gutters keep the lowest courses wet, which is where moss often starts.
• Fix drip sources: downspouts that empty onto a lower roof, or condensate lines that drip on shingles, create permanent wet patches.
• Check attic ventilation: a roof deck that stays cool and damp from below dries more slowly.

Add protection

Zinc or copper strips installed near the ridge release small amounts of metal in rainwater that discourage growth on the roof below, though the effect weakens farther from the strip. At replacement time, algae resistant shingles with copper containing granules help against algae streaks; they are not a complete moss solution, but they pair well with the steps above.

What not to do

Do not pressure wash shingles to prevent moss. It strips granules and shortens roof life. More in moss and lichen on roofs and trees and your roof.