I shop at Atascocita Commons almost every week. It is the big center on FM 1960 near West Lake Houston Parkway. On the drive home, I pass rows of houses in the neighborhoods nearby. One day I noticed how many roofs had long black streaks running down them.
Then I got home and looked at my own. It was the same thing.
My First Guess Was Wrong
I assumed it was mold or dirt. Maybe it was grime from all the traffic on FM 1960. I even thought about renting a pressure washer. Thank goodness I did not.
The Streaks Kept Spreading
Over the next few months, I paid closer attention. The streaks on our roof got longer and darker. They were worst on the side that gets the least sun. A few houses on our street had them too, and they seemed to grow at the same pace.
I asked a neighbor about it over the fence. She had noticed the same thing and figured it was just part of living in Humble. Roof algae streaks in Humble TX neighborhoods are common, she said, but she had no idea what caused them.
That answer did not satisfy me. I wanted to know if the streaks were hurting our roof or just making it look old.
Getting a Real Answer
A coworker told me she had called a roofer about the same streaks. The company was based out in Huffman, not far from us. She said they told her the streaks were not dirt at all. They were algae.
So I booked a visit with a local roofing company she trusted. The inspector confirmed it. He also checked for other problems while he was up there. Our roof had some granule loss and a couple of worn spots near a vent. But the streaks themselves were mostly a looks issue.
What the Experts Say
I wanted to learn more, so I found a guide from the Asphalt Roofing Manufacturers Association. It cleared up a lot.
Here is what I learned:
- Those black streaks are usually algae, not mold or mildew.
- Humid places like ours are perfect for algae growth.
- Wind and animals carry spores from roof to roof. That is why whole streets get streaky.
- By the time you see it, it has likely been there for months.
The guide also says there is no scientific proof that algae harms asphalt shingles. It mostly hurts curb appeal. Moss is a different story. Moss can lift shingle edges, which raises the risk of shingles blowing off in high wind.
The Pressure Washer Mistake
This part surprised me most. The guide warns you to never pressure wash an asphalt shingle roof. It strips off granules and can make the roof fail early.
I was one weekend away from doing exactly that.
Instead, the guide describes a gentle cleaning method. It uses a diluted bleach mix and a low-pressure rinse. It also says to protect the plants nearby. Honestly, I did not want to climb up there with a sprayer.
It turned out the same roofing company offers soft washing, which is the low-pressure kind of cleaning. So I did not have to hunt for a separate crew or trust a guy with a power washer.
How to Slow the Streaks Down
A few tips from the guide seem easy to follow:
- Trim tree branches back so more sun hits the roof.
- Clear leaves and debris off the roof with a leaf blower.
- Keep gutters clean so water drains the right way.
When it is time for a new roof, the guide mentions shingles made with algae-resistant granules. That is something I will ask about when our roof reaches the end of its life.
Worth a Closer Look
If you live near Atascocita Commons and your roof has black streaks, don’t panic. They are common around here. But they are a good excuse to have someone check the rest of the roof. The streaks were not our real problem. The worn spots by the vent were.
I’m glad we found those before they turned into a leak.