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Dark streaks on your roof?

Black streaks are usually algae, and green clumps are moss. Both are fixable, but moss in particular holds water against the shingle and lifts it.

Roof-life assessment

What you’re seeing

  • Black or dark streaks: Usually algae, most often on shaded, north-facing slopes
  • Green clumps: Moss, often along the lower edges and in shaded areas
  • Crusty patches: Lichen, which grips granules and can pull them loose

What causes it

Algae and moss feed on moisture and the materials in shingles. Shade and humidity help them spread, and moss holds water against the roof long after rain stops.

See the seven-stage aging loop

BeforeAfterIllustration

Before and after a soft wash

Drag the handle. The same roof, with algae and moss off and the granules still on.

Can preservation help?

Usually a good candidate

Growth comes off with a low-pressure soft wash, without stripping granules. Once the roof is clean and sound, the SPS System encapsulates it.

  1. Don’t pressure washHigh pressure strips the granules the roof depends on
  2. Soft wash firstroof cleaner at low pressure, then a gentle rinse
  3. Then preserveBaseline readings, then the SPS System