Herndon has plenty of homes tucked under tall trees, especially around Franklin Farm and Fox Mill. Shade keeps the yard cool, and it also keeps roofs damp long enough for streaks and moss to take hold.
The most common signs your roof needs cleaning are black streaks running down the shingles, green patches or moss, a roof that looks older than it is, and spots that stay damp long after rain. All of them point to algae or moss growing on the shingles.
Here are the seven signs to look for and how to clean a roof without damaging it. Our roof cleaning service uses a gentle soft wash, never high pressure.
7 Signs to Look For
Sign 1: Black Streaks on the Shingles
Long black streaks are the classic sign. They are usually an algae called Gloeocapsa magma, not dirt or aging shingles, and they spread over time.
Sign 2: Moss Along the Edges
Moss holds water against the shingles and can lift their edges. It usually starts on the north side and where branches overhang.
Sign 3: Green Patches
A green tint across sections of the roof usually means algae or lichen colonies are spreading.
Sign 4: Leaves and Debris in the Valleys
Debris trapped in roof valleys holds moisture and feeds growth.
Sign 5: Gutters That Fill Up Fast
Granules and organic debris washing off the roof show up in the gutters.
Sign 6: Spots That Stay Damp
If one section is still dark hours after the rest of the roof has dried, it is in heavy shade and prime for growth.
Sign 7: The Roof Looks Older Than It Is
Heavy streaking can make a 10-year-old roof look like it needs replacing, which matters a lot if you plan to sell.
Why You Should Never Pressure Wash a Roof
High pressure strips the protective granules from asphalt shingles, can force water underneath them and can void some manufacturer warranties. The Asphalt Roofing Manufacturers Association specifically warns against power washers and recommends a gentle cleaning solution instead.
For the full breakdown of which surfaces can take pressure, see our guide to pressure washing vs soft washing.
How Professional Roof Cleaning Works
- We soak the plants and grass around the house.
- We apply a soft wash cleaning solution to the roof at low pressure.
- The solution dwells and kills the algae, moss and lichen.
- The next rains rinse the dead growth away, and the streaks keep fading.
Because the roof is never blasted, the granules stay where they belong.
What Causes Black Streaks on Roofs?
The streaks are usually an airborne algae called Gloeocapsa magma, according to the Asphalt Roofing Manufacturers Association. Spores land on the shingles, take hold in the damp, shaded areas and darken as they grow. Rain carries them down the slope, which is why the stains look like long streaks.
Northern Virginia’s humidity and tree cover make it common here, especially on north-facing slopes and under overhanging branches.
Preventing Streaks From Coming Back
- Trim branches that shade the roof or drop debris on it.
- Keep gutters and valleys clear so water drains quickly.
- Schedule a soft wash before the streaks get heavy.
- When it is time to reroof, ask about algae-resistant shingles.
How Often to Clean Your Roof
| Your roof | Suggested schedule |
|---|---|
| Heavy tree cover | Every 2 to 3 years |
| Moderate shade | Every 3 to 4 years |
| Sunny, open lot | Every 4 to 5 years |
| Visible moss or heavy streaks | As soon as practical |
Keeping the gutters clear helps too. See what clogged gutters can do to your home.
Frequently Asked Questions
Are black streaks on my roof harmful?
They are mostly cosmetic at first, but the algae holds moisture and keeps spreading. Over time it can shorten the life of the shingles and makes the roof look much older than it is.
Can I pressure wash my roof myself?
It is not a good idea. High pressure strips shingle granules, can force water under the shingles and can void warranties. It is also dangerous to work on a wet roof.
How long does roof cleaning last?
Most soft-washed roofs stay clean for 2 to 5 years, depending on shade, tree cover and moisture.
Will roof cleaning hurt my landscaping?
Not when it is done properly. We soak plants before and after, so the cleaning solution is diluted and rinsed away.
Does roof cleaning extend the life of the roof?
Removing moss and algae keeps moisture from sitting on the shingles, which helps them last. Roof life still depends mostly on the shingle quality, ventilation and installation, but a clean roof avoids the damage that growth can cause.
Roof Cleaning in Herndon, Done Right
If you spotted any of these signs your roof needs cleaning, a soft wash can bring it back without risking the shingles. Catching it early keeps the job quick.
We serve homeowners in Herndon and nearby Chantilly and Great Falls.
Get your free quote or call 571-364-4466. We answer calls and quote requests 24/7.
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