What Causes the Black Streaks on Your Roof?
Those dark streaks are not dirt or mildew. They are mostly an algae called Gloeocapsa magma, which spreads through the air and grows best in warm, humid places, according to the Asphalt Roofing Manufacturers Association. The streaks show up first on north facing and shaded slopes, where the roof stays damp longer. In Austin, homes under the big live oaks and pecans in Tarrytown, Travis Heights, and Barton Hills often see them within a few years of a new roof.
Owens Corning says it has not seen evidence that algae hurts how asphalt shingles perform, so the streaks are mostly a curb appeal problem. Moss and lichen are different, because they hold moisture against the roof and can lift shingle edges over time. Either way, a streaked roof can make a home look older than it is and bring an HOA notice.
Why We Never Pressure Wash a Roof
High pressure water blasts the protective granules off asphalt shingles. ARMA warns that pressure washing shingles causes granule loss and likely early roof failure, and its cleaning guidance calls for a gentle solution instead. Owens Corning also tells homeowners not to scrub or use high pressure equipment, because it loosens granules and shortens the life of the roof. Pressure can also drive water up under the shingles, where it causes leaks and rot you will not see until later.
If a roof cleaning quote seems very cheap and the crew shows up with only a pressure washer, send them away. The roof may look clean for a season and then age years in a few months.
How We Soft Wash a Roof
Our process follows the same approach roofing manufacturers publish. Owens Corning recommends a mix of bleach and water sprayed on the roof, left for about 10 to 20 minutes, then rinsed while thoroughly flushing the plants around the home. GAF gives similar guidance, with a bleach and water mix applied by sprayer instead of pressure.
Step 1: Protect the Property
We soak all plants, shrubs, and grass below the roof line, and we cover delicate beds. We check that gutters and downspouts are flowing so runoff goes where we want it. Cars, patio furniture, and pets move away from the house.
Step 2: Apply the Soft Wash Mix
We apply a sodium hypochlorite mix at low pressure, about the force of a garden hose. The mix strength depends on how heavy the growth is and what the roof is made of. Our crew works from harnesses tied to roof anchors, never from the edge of a ladder.
Step 3: Let It Work
The mix needs time to kill the algae, moss, and lichen at the root. We do not scrub the roof, because scrubbing removes granules too. Some streaks fade right away, and heavy lichen can keep lightening for a few weeks as rain washes the dead growth off.
Step 4: Rinse and Flush
We rinse the roof gently and flush every plant, bed, and hard surface below it. We also rinse gutters, walls, and windows where runoff landed. Then we walk the property, take after photos, and text them to you.
Roof Cleaning by Roof Type
Asphalt Shingle Roofs
Asphalt shingles are the most common roofs in Austin and the ones that streak the most. We use the manufacturer approved soft wash method described above. Most shingle roofs look like new after one cleaning.
Metal Roofs
Standing seam metal roofs are popular across Austin and the Hill Country. They do not grow algae as fast as shingles, but they collect dirt, pollen, and mildew, and dark metal shows every streak. We use a cleaner made for metal finishes and low pressure, because strong bleach mixes can dull some coatings.
Tile Roofs
Clay and concrete tile roofs are common in Westlake, Lakeway, and Steiner Ranch. Tile is porous, so algae and lichen grow into the surface, and tiles can crack if someone walks on them wrong. We soft wash tile roofs and walk only where the tiles are supported, or we clean from ladders and lifts when needed.
| Roof Type | Our Method | Main Risk With High Pressure |
|---|---|---|
| Asphalt shingle | Soft wash, bleach based mix | Granule loss and early roof failure |
| Metal | Soft wash, metal safe cleaner | Coating damage and water at seams |
| Clay or concrete tile | Soft wash, careful footing | Cracked tiles and surface erosion |
What's Included in Our Roof Cleaning
Every roof cleaning includes all roof slopes, treatment of algae, moss, and lichen, and a check of gutters and downspouts for flow. We protect and flush all landscaping below the roof line and rinse walls and windows touched by runoff. You get before and after photos of every slope. Full gutter cleanouts, house washing, and driveway cleaning can be added to the same visit.
How Much Does Roof Cleaning Cost in Austin?
| Roof Size | Typical Price |
|---|---|
| Up to 2,000 sq ft of roof | $499 to $749 |
| 2,000 to 3,000 sq ft of roof | $749 to $999 |
| Over 3,000 sq ft or steep pitch | $999 to $1,299 |
| Metal or tile roofs | Quoted after a walkthrough |
Price depends on roof size, pitch, height, material, and how heavy the growth is. Steep roofs need more safety setup, and thick lichen may need a second treatment. Adding a house wash to the same visit usually costs less than booking both separately. You always get a written quote before any work begins.
How Long Does a Clean Roof Stay Clean?
Most Austin roofs stay clean for two to four years after a soft wash. Owens Corning notes that cleaning is typically temporary and the streaks can come back, especially on shaded slopes. Trimming branches that hang over the roof helps a lot, because more sun and air keep the roof drier. If you are replacing your roof, ask your roofer about algae resistant shingles, which use copper coated granules to slow algae growth.
Cleaning vs. Replacing Your Roof
Many Austin homeowners think a streaked roof means it is worn out. In many cases, the shingles underneath are still in good shape and only need cleaning. A roof cleaning costs a small fraction of a new roof, so it makes sense to clean first and then decide. If we see damaged, curling, or missing shingles during the estimate, we tell you so you can call a roofer.
Recent Roof Cleaning Projects in Austin
Travis Heights: Asphalt shingle roof with heavy black streaks under live oaks. Low pressure treatment and gentle rinse in about five hours, with all flower beds wetted before and after.
Westlake: Concrete tile roof with lichen and green algae on the north slopes. Soft washed with careful footing on supported tiles, finished in about six hours, with lichen continuing to fade over the next few weeks.
Roof Cleaning FAQs
Will roof cleaning void my shingle warranty?
Will the cleaning solution hurt my plants?
Will you walk on my roof?
Why are some streaks still there right after cleaning?
Do I need to be home?
Get a Free Roof Cleaning Quote in Austin
Send us a photo of your roof from the street, or book a free walkthrough. Call or text (737) 344-9565, or visit our office at 5555 N. Lamar Blvd, Bldg C, Austin, TX 78751. We reply with a written quote within two business hours. There is no cost and no obligation to book.