Is algae on a roof bad?
Short answer. Roof algae is mostly a cosmetic problem: the black streaks rarely damage asphalt shingles on their own. It still matters because it hurts curb appeal and resale, can draw HOA letters, and heavy growth holds moisture that invites moss and lichen, which do cause damage.
What algae does and does not do
- Does not: eat through shingles or cause leaks by itself.
- Does: stain shingles dark, making the roof look older than it is.
- Can: keep the surface damp longer, giving moss and lichen a foothold, especially on shaded north slopes.
- Can: make a light roof absorb a bit more heat as streaks darken it.
Why Georgia roofs get it
Warm, humid weather and shade from trees are ideal for the algae behind black streaks. It spreads by wind, so once one roof in a neighborhood has it, nearby roofs often follow. See black streaks and algae on roofs.
When it is worth removing
- You are listing the house or have an HOA notice.
- Moss or lichen is starting to grow within the streaks.
- The roof is otherwise in good shape with plenty of life left.
When to leave it
If the roof is near the end of its life, cleaning it adds risk and cost for a short lived cosmetic gain. Put the money toward replacement with algae resistant shingles instead.
The real risk is cleaning it wrong
Pressure washing and scrubbing do far more harm than algae ever will, stripping granules that protect shingles from Georgia sun. If you clean, use a gentle bleach soft wash and rinse, and protect landscaping. More on related growth in moss and lichen on roofs.