Black streaks on asphalt shingles are usually a cosmetic algae stain, not damage: the Asphalt Roofing Manufacturers Association (ARMA) says there is no scientific evidence that algae harms asphalt shingles. The streak becomes a roof problem only when it sits next to real damage signs, such as cracked, curled or missing shingles, heavy granule loss in the gutters, moss lifting the shingle edges, or water stains in the attic. Check for those from the ground before anyone books a wash.
Ventura County Roof Cleaning soft washes roofs across Ventura County, and the first question on most streaked roofs is whether the stain is the whole story. For what causes the streaks and how they come off, see black streaks on your roof in Ventura County. For the checks before anyone sprays, see before you remove black streaks from shingles.
Key Takeaways
- The streak itself is cosmetic. ARMA finds no evidence that algae harms shingles, and a National Roofing Contractors Association (NRCA) technical article says manufacturers do not consider the stains harmful to performance.
- Moss is different. ARMA says moss can lift or curl the leading edges of shingles, which raises the risk of blow-off.
- Damage shows up elsewhere. Granules piling in gutters, cracked or curled shingles, loose flashings and attic stains point to the roof, not the stain.
- Check from the ground first. NRCA tells homeowners to stay on the ladder, and off the roof, if possible.
- Order matters. A stain with no damage signs is a cleaning job. A stain with damage signs needs a roofer’s look before any cleaner goes on.
What the Streaks Are, in One Paragraph
Roof algae staining is a dark, surface-only discoloration caused by airborne cyanobacteria that settle on shingles and grow where the roof stays damp. ARMA’s algae discoloration bulletin names Gloeocapsa magma as the most common species behind it. NRCA’s director of technical services wrote in Professional Roofing (April 2009) that surveys found Gloeocapsa “by far the most common cause of dark stains found on asphalt shingle roof systems,” and that “Asphalt shingle manufacturers do not consider algae stains harmful to shingle performance.” The full cause and removal story lives on our Ventura County black streaks guide.
Algae, Moss or Lichen: What Each Means for the Shingle
The growth type decides whether the roof itself is at risk. ARMA’s moss and algae page states: “There is no scientific evidence that algae is damaging to asphalt shingles.” Moss is the exception: it “can cause the leading edges of the shingles to lift or curl, which increases the risk of shingle blow-off,” and it favors north facing roof planes.
| Growth | How it looks from the ground | What it does to the shingle | Next step |
|---|---|---|---|
| Algae | Flat dark streaks running down the slope | Stains the surface; no evidence of harm (ARMA) | Low-pressure soft wash if you want the look back |
| Moss | Raised green or brown clumps, often at the lower edges | Can lift or curl shingle edges (ARMA) | Check the edges, then a staged treatment |
| Lichen | Flat, crusty, gray-green spots that hold tight | Bonds tight to the surface; scraping risks the granules | Leave it alone until a pro sets the method |
If you cannot tell from photos, treat it as moss. Our roof moss and algae guide covers treatment.
Five Signs the Problem Is the Roof, Not the Stain
NRCA’s consumer roofing resources say biannual inspections “often can uncover cracked, warped or missing shingles; loose seams and deteriorated flashings; excessive surface granules accumulating in the gutters or downspouts.” None of those is caused by algae, and none is fixed by cleaning. If you see one next to a streak, the streak is the least of it.
| Sign | Where to look | What it can mean | Who to call first |
|---|---|---|---|
| Granules piling up | Gutters and downspout outlets | The protective surface is wearing away | Roofer |
| Cracked, warped or missing shingles | Ridges, edges and the windward side | Weather damage or an aging roof | Roofer |
| Lifted or curled edges under moss | Lower courses on shaded slopes | Moss working under the shingle (ARMA) | Roofer, then cleaner |
| Loose or rusted flashings | Chimneys, vents, walls and valleys | A likely leak path | Roofer |
| Stains on attic sheathing or ceilings | Attic, below the streaked slope | Water is already getting in | Roofer |
A streak with none of these signs is a cleaning question. A streak with any of them is a roof question, and cleaning first can hide what a roofer needs to see.
How to Check Without Climbing
You can run all five checks without setting foot on the shingles. NRCA’s advice is to “stay on the ladder (and off the roof) if possible,” and wet or algae-covered shingles are slick.
- Walk the perimeter with binoculars or a phone zoom. Photograph each slope in even light. Flat stains and lifted edges look different at full zoom.
- Check the gutters and downspout outlets. Scoop a handful of what has collected. Note whether it is leaves, grit or a layer of granules.
- Look at the flashings. Deteriorated flashings at chimneys, vent pipes and wall joints are on NRCA’s inspection list, and most are visible from the yard.
- Go into the attic on a dry day. Use a flashlight on the sheathing below the streaked slope. Dark rings or soft wood are the warning.
- Get a closer look without foot traffic. If the roof is tall or steep, a drone roof inspection shows the shingle surface and edges without anyone walking on it.
Clean, Repair, or Both: Decide in Order
Whenever damage is found, repair comes before cleaning. A clean roof can make a worn one look healthier than it is.
| What you found | What to do |
|---|---|
| Flat streaks, no damage signs | Cleaning is optional and cosmetic. Book a soft wash if the look bothers you. |
| Streaks plus moss, edges flat | Staged moss treatment, then check the edges again after it weathers off. |
| Moss with lifted or curled edges | Roofer first to judge the shingles, then a cleaning plan. |
| Granule loss, cracked shingles or attic stains | Roofer inspection. Hold any cleaning until the roof’s condition is known. |
| Roof near the end of its life | Talk to a roofer about replacement. See roof cleaning vs. replacement. |
ARMA’s bulletin adds that cleaning is “only temporary, and the discoloration may recur.” That is one more reason to settle the roof’s condition before paying to change its color.
Frequently Asked Questions
How can I tell black streaks from shingle damage?
Black algae streaks are flat, dark bands running down the slope, and the shingle underneath is still intact. Damage shows up as cracked, warped or missing shingles, edges that lift or curl, granules piling in the gutters, loose flashings or stains in the attic. You can check all of these from the ground, the gutters and the attic.
Is it algae, moss or lichen on my shingles?
Algae is a flat dark streak. Moss is raised green or brown growth, often at the lower edges of shaded slopes. Lichen is a flat, crusty, gray-green spot that holds tight to the surface. If you cannot tell from a zoomed photo, treat it as moss until someone looks closer, because moss is the one ARMA says can lift shingle edges.
Do granules in the gutters mean my roof is failing?
Not on their own, but they are worth a roofer’s look. NRCA lists excessive surface granules in the gutters or downspouts among the problems a roof inspection finds. Granules protect the shingle, and no cleaning puts them back, so photograph what you find and have the roof checked before any wash.
Should I clean the roof or call a roofer first?
If the only thing you see is flat streaks, cleaning is a cosmetic choice and a roofer is not needed first. If you see cracked or curled shingles, lifted edges under moss, heavy granule loss, loose flashings or attic stains, call a roofer first. Cleaning does not repair any of those.
Can I check my roof without climbing on it?
Yes. Photograph each slope with binoculars or a phone zoom, check the gutters and downspout outlets for granules, look at the flashings from the yard, and inspect the attic sheathing on a dry day. NRCA advises homeowners to stay on the ladder and off the roof if possible. For tall or steep roofs, a drone inspection avoids foot traffic.
Get the Streaks and the Roof Looked at Together
Ventura County Roof Cleaning soft washes asphalt shingle roofs at low pressure across Ventura County, and we tell you on site when something we see belongs to a roofer instead of a cleaner. We do not publish a fixed price: every job is quoted after a free on-site look at the roof, the growth and the access. Bring your ground photos and we will start from them. Request your free estimate.