Quick Summary: Those unsightly black streaks on your roof aren’t just dirt, they are a living bacteria called Gloeocapsa magma that feeds on the limestone in your shingles. To remove them safely without voiding your warranty, Vineyard Power Washing uses the ARMA-recommended soft wash method. This kills the bacteria at the root, lowers your energy bills, and extends the life of your roof.1
It’s Not Dirt, It’s Alive
If you look at roofs across Oak Bluffs or Edgartown, you will likely see dark, vertical streaks running down the northern slopes. Many homeowners assume this is just dust, soot, or tree sap.
In reality, it is an airborne cyanobacteria called Gloeocapsa magma.
This bacteria thrives in Martha’s Vineyard’s humid, coastal environment. Once the spores land on your roof, they begin to feed on the crushed limestone filler used in modern asphalt shingles.2 As the colony grows, it forms a dark, hard outer shell to protect itself from UV rays. This dark coating is what you see as “streaks” from the street.1
Why You Should Care (Beyond Curb Appeal)
While a dirty roof looks bad, the real damage is financial and structural. Ignoring Gloeocapsa magma can lead to three major issues:
- Reduced Roof Lifespan: As the bacteria eats the limestone, it weakens the shingles, leading to granule loss. Granules are your roof’s “sunscreen”; once they are gone, the asphalt dries out and cracks.3
- Higher Energy Bills: A black, stained roof absorbs significantly more heat than a clean, reflective one. This raises the temperature in your attic, forcing your air conditioning to work harder during the summer season.1
- Insurance Risks: Insurance carriers are increasingly conducting drive-by inspections. If they see heavy algae or moss growth, they may flag the roof as “neglected” and threaten to cancel your policy unless it is cleaned.4
The Solution: Soft Washing (The ARMA Standard)
How do you remove a bacteria that is rooting into your shingles? The Asphalt Roofing Manufacturers Association (ARMA) is very clear on this: Do NOT use a pressure washer.
High pressure (even 1,000 PSI) can blast the granules right off the shingle, effectively aging your roof by 10 years in 10 minutes.
Instead, we use a Roof Soft Washing process. We apply a specialized, biodegradable cleanser that kills the bacteria and lichen on contact. We allow it to dwell for 15-20 minutes to penetrate the root system, and then we rinse it gently, or in some cases, let the rain rinse it naturally over time.
Comparison: Roof Cleaning Methods
| Feature | Soft Washing (Recommended) | High Pressure Washing (Dangerous) |
| Pressure Used | ~60 PSI (Like a light rain) | 1,500+ PSI |
| Impact on Algae | Kills bacteria & spores 100% | Shears off top layer; roots remain |
| Shingle Safety | Granules remain intact | High risk of granule loss |
| Warranty | Approved by Manufacturers | Voids most warranties |
| Result | Lasts 3-5 Years | Streaks return in 6-12 months |
Prevention: The Zinc Solution
Once your roof is clean, we want to keep it that way. Gloeocapsa magma struggles to grow in the presence of certain metals. This is why the area directly below a metal chimney flashing is often clean while the rest of the roof is dirty.
For long-term prevention, we can install thin zinc or copper strips near the ridge of your roof. Every time it rains, tiny amounts of metal ions wash down the slope, creating an invisible shield that prevents new algae spores from taking root.5
A Note on Moss and Lichen
If the black streaks have progressed to thick green moss or lichen, the situation is more urgent. Moss acts like a sponge, holding moisture against the shingle and lifting the edges up, which can lead to leaks during high-wind storms.6
Pro Tip: Spores from your roof often fall onto your patio and walkways, causing them to turn green and slippery as well. If you are scheduling a roof wash, it is often efficient to handle your stone and paver cleaning at the same time to prevent cross-contamination.7
Frequently Asked Questions
Q: Will the cleaning chemicals harm my plants?
A: This is a common concern. We take plant safety seriously. Our process involves pre-soaking all surrounding vegetation with fresh water before we apply any cleaners. We also bag downspouts to capture runoff if necessary. Because the plants are already saturated with water, they do not absorb the cleaning solution, keeping them safe.8
Q: How long does the roof stay clean after a soft wash?
A: Typically, a soft wash will keep Gloeocapsa magma away for 3 to 5 years. However, this depends on the amount of shade your roof gets and the humidity levels on the island.
Q: Can I just scrape the moss off?
A: We strongly advise against dry scraping. Pulling moss off a dry shingle can rip the granules and the fiberglass matting. The moss needs to be killed chemically first so it releases its grip on the shingle.3
Protect your biggest investment.
Don’t let algae shorten the life of your roof. Get a free estimate today and let us safely restore your roof’s appearance and function.