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Blues Home Blog · April 2026

Dark Streaks on Your DFW Roof: What They Are and How to Remove Them

Those dark streaks spreading across your DFW roof are living organisms that are actively damaging your shingles — here's how to safely remove them.

By Altair Khalilbayov, Owner — Blues Home Services

What Causes Dark Roof Streaks

The dark streaks you see spreading across roofs throughout DFW neighborhoods are caused by gloeocapsa magma — a type of cyanobacteria that feeds on the limestone aggregate in asphalt shingles. The bacteria grows in colonies that appear as dark gray to black streaking, typically beginning on shaded, north-facing slopes where moisture retention is highest.

Left untreated, the bacteria spread progressively across the entire roof surface, absorbing heat and accelerating UV degradation of shingles. Insurance companies and roofing manufacturers recognize extensive biological growth as a contributing factor in premature shingle failure.

The Only Manufacturer-Approved Removal Method

The Asphalt Roofing Manufacturers Association (ARMA) recommends low-pressure soft washing with a sodium hypochlorite solution as the safe removal method. High-pressure roof washing strips granules from asphalt shingles and voids most manufacturer warranties — it must be avoided.

Blues Home Services uses ARMA-compliant soft washing for all DFW roof cleaning. We apply biodegradable algaecide at low pressure, allow appropriate dwell time for the chemistry to kill biological growth at the root, and include a post-treatment application. The results are immediately visible — and the algaecide continues working after we leave.

Organic Growth: Why It Comes Back If You Only Clean the Surface

Algae, mildew, and lichen are living organisms, not stains — and that changes how they have to be treated. Blasting growth off with pressure removes the visible layer but leaves the root structure behind, which is why pressure-only cleaning sees regrowth within months. Soft washing solves this: a low-pressure application of a biocidal cleaning solution that kills the organism completely, so surfaces stay clean several times longer.

What Actually Drives the Price

The estimate is really a labor forecast: bigger areas, heavier buildup, and awkward access each add hours, and hours are what you are paying for. Buildup is patient and compounding; the gap between a maintenance clean and a recovery job widens every season the work is postponed. Bundling is the one discount that costs nobody anything — the crew is already on site, the equipment is already staged, and the savings pass straight through. A serious bid reads like a work plan; a suspicious one reads like a phone number with a dollar sign.

A Realistic Annual Rhythm for North Texas Homes

A DFW exterior calendar works backward from the weather: prepare before spring storms, recover after them, protect ahead of summer heat, and reset in fall. Build the calendar around the non-negotiables first — gutters ahead of the wet months, sealing in the mild ones — then slot windows and flatwork into whatever cadence the property's exposure demands. Routine is the discount: crews work faster on surfaces they maintained last time, and nothing on the property ever gets far enough gone to need rescue pricing.

A Local Crew, Not a Franchise

This is owner-operated service in the literal sense: the standard set on our first job is the standard enforced on every job since. Most services book within the week, estimates are always free, and we confirm arrival windows so nobody waits around wondering. The reviews we earn come from one policy: the job is finished when the homeowner says it is, not when the crew packs up.

By the Numbers

Purified water used for professional window cleaning is processed to 0–10 parts per million of dissolved solids — North Texas tap water commonly carries many times that mineral load.

Source: North Texas municipal water quality reports; window cleaning industry TDS standards

The U.S. Geological Survey classifies water above 121 mg/L of dissolved minerals as “hard” and above 180 mg/L as “very hard” — North Texas municipal supplies commonly test in the hard-to-very-hard range in annual water quality reports.

Source: U.S. Geological Survey water hardness classification; North Texas Municipal Water District and City of Fort Worth annual water quality reports

Frequently Asked Questions

They are colonies of Gloeocapsa magma, a hardy blue-green algae that feeds on the limestone filler in asphalt shingles. It shows up as black or gray streaks, usually first on north-facing and shaded slopes where moisture lingers. In humid North Texas summers it spreads steadily and darkens the whole roof over time.
No, and it can cause real harm. High pressure strips the protective granules off shingles and voids many manufacturer warranties. The accepted method is low-pressure soft washing with a cleaning solution that kills the algae at the root. That treatment removes the staining without eroding the shingle surface.
A proper soft-wash treatment kills the existing algae so results last considerably longer than a surface rinse, often years depending on shade and moisture. Regrowth eventually returns because spores travel on the wind. Homes with heavy tree cover or damp, shaded roof sections tend to see it reappear sooner than sun-exposed ones.

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Blues Home Services serves Southlake, Frisco, Flower Mound, Colleyville & the Dallas-Fort Worth area.