Black Streaks on Your Home Exterior: What They Are and How to Remove Them

# Black Streaks on Your Home Exterior: What They Are and How to Remove Them

If you have noticed dark, streaky discoloration running down your siding, brick, or roof shingles, you are not imagining it getting worse every year. Those black streaks are alive — and in a climate like Charlotte, NC, they thrive.

Understanding what you are dealing with makes it a lot easier to know how to fix it — and why power washing alone often does not cut it.

What Causes Black Streaks on Siding and Roofs

The culprit is almost always a cyanobacterium called *Gloeocapsa magma*. It feeds on the limestone filler used in asphalt shingles and the moisture trapped in porous siding materials. In the Southeast, where summers are humid and homes sit under tree canopy for much of the year, conditions are basically ideal for this organism to spread.

You will also see it on:

• Vinyl siding on north-facing walls that stay damp longer
• Brick and stucco that retains moisture
• Painted wood siding, especially near gutters and downspouts
• Concrete driveways and walkways (though this is usually a different organism, often mold or mildew)

Left alone, the streaking compounds over time. Algae retains moisture against your siding, which accelerates degradation of paint and exterior materials. On a roof, it can shorten shingle life by years.

Why Pressure Washing Alone Does Not Work

High-pressure washing will blast the visible streaks off. But the root system of the algae is embedded in the surface — and pressure alone does not kill it. Within one to two seasons, the same streaks return, usually worse.

This is the core reason professional house washing services use a low-pressure soft wash approach combined with a surfactant-based cleaning solution. The solution kills the organism at the root. The soft wash rinse removes it without damaging vinyl, painted wood, or roofing materials.

Pressure washing a roof, specifically, can strip granules from shingles and void manufacturer warranties. It is one of the most common DIY mistakes homeowners in Charlotte make when they spot algae.

How Professional House Washing Removes Black Streaks

A proper exterior cleaning for algae and biological growth follows this process:

1. **Pre-treatment**: A professional-grade cleaning solution (typically sodium hypochlorite based at the correct dilution) is applied at low pressure to dwell on affected surfaces.

2. **Dwell time**: The solution is left to break down the algae, mold, or mildew — typically 10 to 20 minutes depending on severity and temperature.

3. **Soft wash rinse**: Low-pressure water removes the dead growth and cleaning solution without damaging the surface.

4. **Gutter and detail clean**: Downspout channels and fascia are cleared of residue since they are common re-infestation points.

For most Charlotte homes with moderate streaking, a single soft wash treatment produces dramatic results. Severe cases — heavy green mold on north-facing walls, deep algae staining on aging vinyl — may need a second pass.

How Long Does It Last?

After a professional soft wash, most homeowners see clean results that last 18 to 36 months. Factors that accelerate regrowth:

• Heavy tree coverage that blocks sunlight and traps moisture
• Gutters that overflow and create wet streaks down siding
• Properties near water or in low-drainage areas

Some cleaning services offer a maintenance plan — a lighter annual soft wash touch-up — to prevent streaks from coming back before they become visible. For homes where curb appeal matters (rentals, homes preparing to list, HOA neighborhoods), this is usually worth the cost.

When to Call a Professional

If the streaking on your siding or roof has been building for more than one season, a DIY cleaning attempt with a big box store pressure washer will likely disappoint. The surface may look cleaner for a few weeks, but without the right chemistry, the algae comes back fast.

For homeowners in Charlotte and surrounding areas who want it done right the first time, a professional soft wash service is the most efficient path. Done correctly, it restores curb appeal, protects your exterior materials, and buys you years before you have to think about it again.