Black Streaks on Your Roof in Coastal Georgia: Causes & Fix

Dirt or mold is what people think it is. Most homeowners assume they have to scrub the roof or replace the shingles. Either one is something you do not need to do.

It is algae, not dirt

A blue-green algae called Gloeocapsa magma causes that black streaking on asphalt shingles. Wind and birds carry it from roof to roof. It eats the limestone filler used as a binder in most shingles. The algae makes a dark, UV-protective pigment as colonies grow. The streak is that pigment. It is not soot or mold, and your roof is not failing.

Why coastal Georgia roofs get it worse and faster than inland roofs

Gloeocapsa magma spreads because of moisture and warmth. This coast has both almost all year. Roofs stay wet longer than inland areas due to humidity from the marsh and ocean. Unlike a hard freeze up north, mild winters here don't kill the algae. Live oaks on many Brunswick and island lots shade roofs so the north-facing side stays damp all day. That is what the algae wants. You see streaks in three to five years. That happens inside a shingle's rated lifespan.

Why scrubbing or pressure washing makes it worse

On those streaks you might want to use a pressure washer. Don't do it. Asphalt shingles lose their granules from high pressure. Without those granules, UV and water hit the shingle directly. It was not designed for that. This can shorten the life of the roof and void the manufacturer's warranty. Scrubbing does similar damage on a smaller scale.

Soft washing removes it without damaging the shingles

A low pressure soft wash is the correct method. We apply a cleaning solution to the roof that kills the algae down at the root. It is given time to work and then rinsed off gently rather than blasted. No granules are lost and no shingles are lifted. The roof comes back close to its original color because the algae is dead, not just knocked loose from the surface. See our roof cleaning service for how we run a soft wash roof job start to finish. This includes how we protect gutters, landscaping and anything below the roofline during the rinse.

Roof after soft wash algae removal, Brunswick GA

Metal and tile roofs get streaks too

Metal and tile roofs on the coast develop the same dark algae streaking and mildew growth in shaded, humid spots too. Asphalt shingles are the most common host because of the limestone filler, but moss grows in valleys and around vents. The soft wash approach is the same regardless of roofing material. Only the dwell time and solution strength change. Streaked shingles often run right down into the gutters too. A roof soft wash is a natural time to add clearing the gutters below a streaked roof to the same visit.

Will it come back?

Those streaks will eventually return because the spores stay in the air along this coast. A soft washed roof usually stays clean for multiple years depending on shade and exposure. That is longer than the three-to-five-year cycle of an untreated roof. Some homeowners put a zinc or copper strip along the ridge as a deterrent. We can talk about that when we look at your roof.

Frequently Asked Questions

Are the black streaks on my roof actually mold?

Up there it isn't mold or dirt. Gloeocapsa magma is the species of algae. The dark pigment that makes the streaks is produced when they eat the limestone in shingles.

Does roof algae mean my roof is failing?

Your roof won't leak just because of the algae. The streaking is cosmetic. The algae is shielded from UV by the pigment. The life of the shingles can be shortened if you leave it for years. A structural problem is not what it is a sign of.

Can I pressure wash the streaks off myself?

Keep pressure washers away from the roof. Asphalt shingles have their granules stripped by pressure. The roof's life is shortened by this and the manufacturer's warranty can be voided. Without that risk, a soft wash gets the algae off.

How long does a soft washed roof stay clean?

It varies with shade and sun exposure. A properly soft washed roof typically outlasts the three-to-five-year cycle an untreated roof shows before streaking returns.

Get your roof looked at

(912) 571-0639

Call or text (912) 571-0639 for a free look if your roof has started to streak. We will tell you honestly whether it needs a soft wash now or can wait. We never recommend pressure on a shingle roof. If you are weighing the roof against the rest of the property, our guide to what changes the price of a house wash covers the same kind of factors for the walls.

Call (912) 571-0639 for a Free Quote

What Causes the Black Streaks on Roofs in Coastal Georgia?