What causes algae growth on shingles, and how do algae resistant shingles stop it?
How the streaks form
The common culprit is a blue-green algae that spreads by airborne spores. It colonizes damp areas and forms a dark protective coating as it grows, which is why roofs look streaked, usually starting below the ridge and running downhill as rain carries it. North Georgia's humidity and tree cover give it plenty of chances.
How algae resistant shingles work
- Copper granules: a portion of the surface granules carries copper that slowly releases with rain and dew, discouraging growth.
- Time limited: the protection fades as the copper is used up, which is why algae warranties run for a set number of years.
- Labeled packages: warranty coverage applies only to products sold in packages bearing the algae protection logo.
Examples of the coverage
GAF's Timberline HDZ carries a 25-year StainGuard Plus algae protection limited warranty on packages with that logo, and Timberline UHDZ carries a 30-year StainGuard Plus PRO warranty on labeled packages. Other lines and manufacturers have their own terms, so read the specific product sheet.
If your current roof already has streaks
- Streaks are mostly cosmetic and do not usually mean the roof is failing.
- Gentle cleaning following the shingle maker's guidance can remove them; avoid pressure washing.
- Zinc or copper strips near the ridge help prevent regrowth below them.
- Heavy algae alongside moss or lichen is worth an inspection.
Color matters
Streaks show far more on light and medium colors than on dark ones. Read black streaks and algae on roofs and best shingle colors for Georgia heat.