Click to call us at (360) 609-7035 📞
Black streaks on Portland roofs are caused by Gloeocapsa magma, a cyanobacteria that feeds on limestone in asphalt shingles. It thrives in Portland's humid climate and requires soft washing to remove safely.
If you've noticed black streaks running down your Portland roof, you're not alone. These dark stains appear on homes across the Pacific Northwest, and they're not caused by dirt, tree debris, or pollution.
The culprit is Gloeocapsa magma, a cyanobacteria that feeds on the limestone in your asphalt shingles. Portland's climate creates ideal growing conditions for this organism, which is why so many local roofs develop these streaks.
Despite being commonly called "roof algae," Gloeocapsa magma is actually a cyanobacteria. It thrives in humid environments with moderate sunlight, which describes Portland for much of the year.
The bacteria itself is blue-green, but it produces a dark protective coating to shield itself from UV rays. This dark coating is what creates the visible black streaks on your shingles.
Modern asphalt shingles contain limestone fillers that the bacteria feeds on. Older shingles made primarily from asphalt and felt rarely had this problem. Today's shingles with fiberglass and limestone content are more vulnerable.
Portland sits in the Pacific Northwest's prime zone for roof algae growth. Several factors make local roofs susceptible:
Climate conditions:
The bacteria needs some sunlight to grow but not too much. Portland's typical 3 hours of bright sunshine per day in winter months and overcast conditions much of the year create perfect growing conditions.
North-facing roof sections often show worse staining because they receive less direct sun and stay damp longer.
Black streaks from algae cause gradual damage if left untreated for years:
How it harms shingles:
Algae alone won't destroy your roof quickly. But combined with moss, which commonly follows algae growth, the damage accelerates significantly. Understanding the difference between moss and algae helps you identify what's growing on your roof.
The most important rule: never pressure wash asphalt shingles. High-pressure water strips away protective granules and dramatically shortens roof life.
Safe removal methods:
DIY cleaning with a garden hose and appropriate cleaning solution can work for minor staining. For extensive black streaks covering large roof sections, professional roof cleaning ensures proper technique without damage.
Soft washing costs approximately $0.30 to $0.60 per square foot. For a typical 1,700 square foot Portland roof, expect to pay $500 to $1,000 for professional treatment.
Once you've cleaned your roof, prevention helps extend the results:
Maintenance steps:
If you're replacing your roof, consider algae-resistant shingles. These contain copper granules that inhibit bacteria growth and cost about 10-20% more than standard shingles.
Sometimes dark staining signals more than just algae. Check for:
If your roof shows multiple types of staining or significant moss buildup, address both issues together for best results.
Black streaks on your Portland roof don't require emergency action, but they shouldn't be ignored for years either. Early treatment prevents the bacteria from weakening your shingles and creating conditions for moss growth.
Schedule a professional roof cleaning to safely remove black streaks and protect your roof from further damage.
-p-130x130q80%20(1)%20(1).png){kind=icon}
We earn trust by delivering a consistently great experience. Clients return year after year, confident they’ll receive the same high-quality service.
-p-130x130q80%20(1)%20(1).png){kind=icon}
Our skilled crews provide workmanship that impresses and holds up over time.
.png){kind=icon}
We offer fair, competitive pricing so customers can enjoy top-tier service without stretching their budget.