What the Black Streaks Actually Are

Drive through any Bossier City neighborhood, from the established streets off Benton Road to the newer subdivisions south of I-220, and you will see black streaks running vertically down asphalt-shingle roofs, especially on the north and east faces. Most homeowners assume it is dirt, soot, or runoff. It is none of those.

The streaks are colonies of gloeocapsa magma, a cyanobacteria (technically a blue-green algae) that feeds on the limestone filler used in modern asphalt shingles. Limestone became standard in shingle manufacturing in the 1980s as a cheap inert filler. The downside: gloeocapsa magma loves it, and the Red River corridor gives the algae everything else it needs to thrive nearly year-round.

Once a colony establishes, it spreads roughly one to three feet per year and produces a dark protective sheath that shields it from sunlight. That sheath is what you see as black streaks. It also absorbs solar heat the shingle was designed to reflect, which heats the roof deck underneath and shortens shingle lifespan, a real problem under a long Louisiana summer.

Why the River Makes It Worse Here

Bossier City sits right on the Red River, and that water keeps the air over Bossier Parish heavy with moisture most of the year. Algae needs three things to grow: a food source, warmth, and moisture. The shingles supply the food, the long warm season supplies the heat, and the river supplies a steady stream of the moisture. That is why roofs here often streak faster than roofs an hour inland, and why a home backed up to the river or a bayou tends to regrow growth sooner after a cleaning.

Why You Cannot Pressure-Wash an Asphalt Roof

The Asphalt Roofing Manufacturers Association (ARMA) explicitly warns against pressure-washing asphalt shingles. The reason is simple: the colored ceramic granules on top of each shingle protect the asphalt underneath from UV damage. High-pressure water strips those granules. Once they are gone, the shingle ages five to ten years overnight under direct sunlight.

Most major shingle manufacturers (GAF, Owens Corning, CertainTeed, Atlas, Tamko) require ARMA-compliant cleaning to keep warranties valid. Pressure-washing a roof can void a 30-year warranty in a single afternoon. We have seen Bossier City homeowners with eight-year-old roofs that look twenty-five because a previous service used a pressure washer.

Soft washing solves this. Instead of relying on water pressure to remove the algae, soft washing uses a low-pressure (under 100 PSI, about the same as a garden hose) application of cleaning chemistry that kills the algae at the root. The next Louisiana rainstorm rinses the dead growth off.

The Chemistry: What Actually Works

The ARMA-recommended chemistry is a sodium hypochlorite solution mixed with a surfactant. Sodium hypochlorite is the active ingredient in household bleach but at a higher working concentration. The surfactant lets the chemistry cling to vertical surfaces long enough to kill the algae before rinsing off.

We apply this with a 12-volt soft-wash pump that delivers chemistry at fire-hose pressure (about 60 to 80 PSI), well below the granule-stripping threshold. The application takes 30 to 60 seconds per roof section, the chemistry sits for 10 to 15 minutes, then we rinse with plain water. Total time on a typical 2,500 square foot Bossier City roof is 60 to 90 minutes.

The chemistry biodegrades quickly. We pre-rinse and post-rinse all landscape beds within the perimeter of the house. Bossier City homes with mature azaleas under the eaves get extra care because azaleas are sensitive to chemistry runoff.

How Often Bossier City Roofs Need It

Every 3 to 5 years for asphalt shingles in this humidity. North-exposed roofs, homes with heavy tree shade, and houses near the river or a bayou may need closer to 3 years because the constant damp regrows the algae faster. Sun-exposed roofs in newer open subdivisions can sometimes stretch toward 5 years.

If the streaks have been ignored for ten or more years, the first cleaning dramatically restores the roof to factory color. Subsequent cleanings every few years keep new colonies from establishing and keep the roof looking new for the rest of its lifespan. We also offer an optional zinc-strip ridge installation that releases trace zinc oxide during rain to slow regrowth for 5 to 10 years. The strip is invisible from the ground.

What About Moss and Lichen

Black streaks (gloeocapsa magma), moss, and lichen are three different organisms that grow differently on Bossier City roofs. Moss grows in thick green patches in shaded valleys and behind chimneys. Lichen attaches as raised crusty spots that resist plain pressure cleaning. Each needs the same soft-wash method but a different application sequence. Moss often needs a longer dwell time before rinsing; lichen sometimes needs a light manual lift after the chemistry kills it. We identify each on the quote so the price is accurate.

Why the DIY Route Backfires

Every spring a few Bossier City homeowners try to handle the streaks themselves, and it almost always ends up costing more than the wash would have. The rented pressure washer strips granules and voids the warranty, as covered above. The big-box roof-cleaning concentrate sold for a garden sprayer is too weak to kill gloeocapsa at the root, so the streaks fade for a month and come roaring back. And the real hazard is the ladder. A wet, algae-slick roof is one of the most dangerous surfaces a homeowner can stand on, and a Louisiana asphalt roof in summer is soft enough to scuff under a boot. We soft-wash the great majority of a roof from the ground or off a stable ladder at the edge, with the proper reach and fall protection, precisely so nobody has to walk a slick slope. The savings from doing it yourself disappear the first time a warranty is voided or somebody comes off a ladder.

The Signs It Is Time

You do not have to wait until the whole roof is black. A few early signals tell you the algae has taken hold and is worth treating before it spreads. The first streaks almost always show on the north and east faces, the slopes that stay shaded and damp longest in the Bossier City humidity, so that is where to look first. Dark spotting around the base of a chimney or in a roof valley usually means moisture is collecting there and moss is not far behind. And if a neighbor two doors down just had their streaks cleaned while yours are creeping in, that is your cue, because gloeocapsa spreads roof to roof through the air. Catching it early keeps the cleaning to a simple maintenance wash instead of a heavier restoration years later.

Common Questions

How long does a Bossier City roof cleaning take?

A standard 2,500 square foot asphalt roof takes 60 to 90 minutes start to finish. Larger homes with multiple roof planes or steep pitches take two to three hours.

Will the chemistry hurt my landscaping?

No. We pre-rinse, tarp, and post-rinse every landscape bed within the perimeter of the house. The chemistry breaks down quickly and we manage the runoff so nothing pools on your plants.

How long do the results last in Bossier City?

A single cleaning lasts 3 to 5 years before new colonies become visible. Roofs near the river or under heavy shade trend toward the shorter end. A zinc-strip ridge installation extends results to 5 to 10 years.

Why does my roof streak faster than my cousin’s in a drier town?

The Red River keeps Bossier City air humid year-round, and humidity is exactly what gloeocapsa magma needs. More moisture means faster algae growth, so river-metro roofs streak sooner than roofs an hour inland.

Can I just clean the streaks myself with a store-bought roof cleaner?

We do not recommend it, and it usually costs more in the end. The garden-sprayer concentrates sold at big-box stores are too weak to kill gloeocapsa at the root, so the streaks come back in a month. A rented pressure washer strips granules and voids the warranty. And a wet, algae-slick roof is genuinely dangerous to walk. A professional soft-wash from the ground kills it for years without the risk.

Is soft washing safe for a 25-year-old roof?

Yes. Soft washing is gentler than rain. The chemistry kills the algae and gravity rinses dead growth on the next rainstorm. There is no abrasive contact with the shingles at all.

Read more on our Bossier City Roof Cleaning service page, our Bossier City overview, or see our recent project gallery.