Living on Martha’s Vineyard brings unique charms – ocean breezes, salt air, and lush greenery. But those same elements often bring an unwelcome guest to your home’s exterior: dark, unsightly streaks on your roof.
If you’ve looked up recently and asked, “Why are my roof shingles black?”, you aren’t alone. It is one of the most common questions we get at Vineyard Power Washing. While many homeowners assume it’s just dirt, soot, or tree sap, the culprit is usually something much more alive.
In this guide, we’ll break down exactly what is eating your shingles, the difference between algae and moss, and how to safely clean your roof without damaging it.
It’s Not Dirt – It’s Gloeocapsa Magma
The black streaks running down your roof are actually a type of blue-green algae known as Gloeocapsa magma.
Why does it turn black? To protect itself from the sun’s UV rays, this algae produces a dark, pigmented sheath – essentially a natural sunscreen. As the colony grows, these dark spots merge into the tell-tale streaks that ruin your home’s curb appeal.
Why It Loves Martha’s Vineyard
Our island climate is the perfect incubator for roof algae:
- Humidity: Algae thrives in moisture. The Vineyard’s humid summers and coastal dampness allow spores to take hold easily.
- Food Source: Modern asphalt shingles contain crushed limestone (a filler material). Gloeocapsa magma feeds on this limestone, literally eating away at the integrity of your roof over time.
- Shade: While algae can grow anywhere, it spreads fastest on the north side of roofs or areas shaded by our beautiful oak and pine trees, where moisture lingers longer.
Algae vs. Moss: What’s the Difference?
While black streaks (algae) are unsightly, moss is structurally dangerous.
Moss is a plant with a root system. As it grows on your roof, its roots can grow underneath the shingles, lifting them up. This breaking of the seal allows wind-blown rain to get underneath the roofing material, leading to rotting wood, leaks, and costly repairs.
On Martha’s Vineyard, we often see a “Double Whammy”: the algae creates a layer of organic material that holds moisture, which then allows moss and lichen to take root. If you see black streaks today, you might see moss tomorrow.
The Solution: Why You Should NEVER Pressure Wash a Roof
When homeowners see a dirty roof, their first instinct is often to blast it with high pressure. Do not do this.
Using a high-pressure washer on asphalt shingles is like taking a sandblaster to them. It strips away the protective granules that reflect the sun and protect your home from the elements. Once those granules are gone, your roof ages prematurely, and your warranty is likely voided.
The Vineyard Power Washing Approach: Soft Washing
At Vineyard Power Washing, we use a method recommended by roofing manufacturers called Soft Washing.
How Soft Washing Works:
- Low Pressure: We use water pressure roughly equivalent to a garden hose.
- Specialized Cleansers: We apply a biodegradable, eco-friendly cleaning solution that kills the algae and moss at the root (molecular level).
- Long-Lasting Results: Unlike pressure washing, which just blasts the top layer off (leaving the roots to grow back in weeks), soft washing sanitizes the surface. This keeps your roof cleaner for up to 3-5 years.
Read More: Learn about our specific process for Roof Soft Washing on Martha’s Vineyard.
Prevention: Keeping Your Vineyard Roof Clean
Once we have restored your roof to its original beauty, there are a few steps you can take to keep it that way:
- Trim Overhanging Branches: Sunlight is the natural enemy of algae and moss. trimming back branches increases airflow and sunlight, helping your roof dry out faster after a rain.
- Zinc Strips: Installing a zinc or copper strip at the peak of your roof can help. When it rains, trace amounts of metal ions wash down the roof, creating an environment where algae cannot grow.
- Regular Maintenance: Don’t wait until the moss is lifting your shingles. Schedule a House Washing or roof inspection every few years to catch growth early.
Ready to Restore Your Roof?
Don’t let black streaks or moss shorten the life of your roof. Restoring your home’s curb appeal is safer, faster, and more affordable than a roof replacement.
Contact Vineyard Power Washing today for a free estimate and let us make your shingles look new again.
FAQ: Roof Cleaning on Martha’s Vineyard
Q: Why are my roof shingles black on the north side only?
A: The north side of your roof receives the least amount of direct sunlight. This allows moisture to stay on the shingles longer, creating the perfect damp environment for Gloeocapsa magma (black algae) to grow and spread.
Q: Will the cleaning solution harm my plants or pets?
A: No. We take great care to protect your property. We pre-soak and rinse all landscaping before, during, and after the process to dilute any run-off. Our soft wash solutions are biodegradable and safe for your home’s ecosystem when handled by professionals.
Q: Can I just scrape the moss off myself?
A: We advise against it. Scraping moss often rips the granules off the shingles along with the root system. It is much safer to kill the moss chemically via soft washing so it detaches naturally without damaging the shingle surface.
Q: How often should I clean my roof on Martha’s Vineyard?
A: Due to the coastal humidity, most Vineyard homes benefit from a roof cleaning every 3 to 5 years. However, homes heavily shaded by trees may need attention sooner.
Q: Does cleaning the roof extend its lifespan?
A: Absolutely. By removing algae (which eats the limestone) and moss (which lifts shingles), you allow the roof to function as intended, potentially adding years to its life and saving you from a premature replacement.