Roof Cleaning in Utah: Moss, Algae & Black Streaks

Roof cleaning removes the moss, algae, and black streaks that grow on shingles, and it should be done with a low-pressure soft-wash, never a pressure washer that strips granules off your roof. Done right, it protects the roof. Done wrong, it ruins it.

Here is what is actually growing up there and how to deal with it.

What causes the gunk on your roof

Three different things show up on Utah roofs, and they are not the same problem:

• Black streaks are caused by a blue-green algae called gloeocapsa magma. It feeds on the limestone filler in asphalt shingles and leaves dark vertical stains.
• Algae and mildew thrive on the north-facing and shaded sides of a roof where moisture lingers.
• Moss grows where debris collects and stays damp, often under trees, and it can lift shingle edges as it spreads.

In Utah, you see more of this on shaded slopes and in canyon-adjacent neighborhoods where roofs hold moisture longer.

Soft-wash vs. pressure washing

This is the part that matters most. A pressure washer blasts away the protective granules that shield your shingles from UV. You might get a clean roof for a season, but you will have taken years off its life and possibly voided the shingle warranty.

Soft-washing uses low pressure and a cleaning solution that kills the algae and moss at the root, then rinses gently. The growth dies and weathers off over the following weeks without tearing up the shingle surface. For asphalt shingles, soft-wash is the only safe method.

Why cleaning matters

It is not only about looks. Moss holds moisture against the shingles and can lift their edges, letting water underneath. Algae slowly degrades the shingle surface. Left long enough, growth shortens the life of a roof that might otherwise have years left.

Cleaning, then renewing

Cleaning solves the surface problem, but it does not address shingles that are already drying out from years of Utah sun. If your roof is aged but still sound, cleaning it and then rejuvenating it is a strong combination: you remove the growth and restore the shingles' flexibility, all for a small fraction of what a new roof costs.

When cleaning is not enough

If your roof is already failing, leaking, or has widespread missing shingles, cleaning is cosmetic at best. A clean failing roof is still a failing roof. In that case the money belongs in repair or replacement, not a wash.

If you are not sure whether you are looking at a surface problem or a worn-out roof, a free inspection will tell you the difference, so you spend on the right fix instead of just the pretty one.

FAQ

Can you pressure wash an asphalt shingle roof?

No. Pressure washing strips the protective granules off asphalt shingles, shortens the roof's life, and can void the shingle warranty. Asphalt roofs should be cleaned with a low-pressure soft-wash that kills algae and moss at the root and rinses gently without damaging the surface.

What causes black streaks and moss on a roof?

Black streaks come from gloeocapsa magma algae that feeds on the limestone filler in shingles. Moss grows where debris and moisture collect, often on shaded or north-facing slopes. Both are more common in Utah neighborhoods near canyons and trees where roofs stay damp longer.

Does roof cleaning fix an old roof?

Cleaning removes surface growth but does not restore shingles that have dried out from age and UV. On a sound but aging roof, cleaning followed by rejuvenation addresses both issues for a fraction of a replacement. On a failing roof, cleaning is cosmetic and the money is better spent on repair or replacement.