If your Columbus-area home has dark streaks running down the roof, you're looking at Gloeocapsa magma — a cyanobacteria that feeds on limestone filler in asphalt shingles and is endemic to Ohio's humid climate. Here's everything you need to know.
What Are Those Black Streaks?
The dark staining that appears on Ohio roofs — particularly on north-facing and shaded slopes — is not dirt, aging, or weather damage. It's Gloeocapsa magma, a photosynthetic cyanobacteria that thrives in humid environments. Ohio's high summer humidity makes it one of the most prevalent roof algae states in the country. The organism spreads via airborne spores, which is why you often see it jump from roof to roof in a neighborhood over a few years. It's biological, active, and actively consuming your shingles.
Why It's More Than Cosmetic
Gloeocapsa magma feeds on the calcium carbonate (limestone) granules that give asphalt shingles their UV protection. As the organism spreads, it depletes the granules that shield the underlying asphalt from UV degradation. The dark pigment the bacteria produces also absorbs additional heat, raising roof surface temperatures and accelerating the breakdown of shingle flexibility. Studies have shown algae-covered roofs can fail 10–15 years earlier than clean roofs — a $12,000–$20,000 difference for a Columbus home roof replacement.
Pro Tip: Look in your gutters for granule accumulation. Excessive granule loss is a measurable sign that algae is actively degrading your shingle surface.
What Is Soft Washing?
Soft washing uses a low-pressure application (under 500 PSI) of a biodegradable cleaning solution — typically a sodium hypochlorite-based mix — that kills the algae, bacteria, mildew, and moss at the cellular level. The solution is applied with a garden-hose-level pressure, allowed to dwell for a controlled period, and then gently rinsed. There is no scrubbing, no high pressure, and no physical impact to the shingle surface. The cleaning chemistry does all the work. The ARMA (Asphalt Roofing Manufacturers Association) endorses this method as the only safe approach for asphalt shingle cleaning.
How Long Do Results Last?
A professional soft wash treatment kills existing algae growth completely. Unlike pressure washing — which just blasts off the surface layer while leaving roots behind — chemical treatment eliminates the organism entirely. Results typically last 2–5 years depending on shade, tree proximity, and how heavily the neighborhood is affected. We offer preventative treatment options that can extend clean periods even further by treating shingles with a residual inhibitor after cleaning.
What About Moss and Lichen?
Moss and lichen are more aggressive than algae and take longer to respond to treatment. Moss lifts shingle edges, allowing water infiltration. Lichen actually chemically bonds to the shingle surface and must be treated and then allowed to die before removal — attempting to physically scrape lichen off damages shingles severely. Both require professional-grade chemistry and patience. We leave treated moss and lichen in place after treatment — it dies and washes away with rain over the following weeks, without any physical disturbance to the shingles.
- Algae (dark streaks): Responds quickly to single treatment
- Moss (green carpet growth): Requires treatment + time to die fully
- Lichen (crusty patches): Hardest to remove — must die before gentle clearing
- All three: Never use high pressure — physical scrubbing causes more damage
When to Schedule Roof Cleaning in Ohio
Spring and fall are the ideal windows for roof soft washing in Central Ohio. Spring treatments address algae that established during the humid summer prior and survived winter. Fall treatments prevent new growth from taking hold over winter when roofs are wet for extended periods. We recommend not waiting until you can clearly see streaking from the ground — by that point the organism has already been active for 1–2 years and has caused measurable granule loss.
Frequently Asked Questions
Black streaks on Ohio roofs are almost always Gloeocapsa magma — a cyanobacteria that feeds on limestone filler in asphalt shingles. It's endemic to Ohio due to high summer humidity and spreads via airborne spores, which is why you often see it jump from roof to roof in a neighborhood.
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