Utah roofs
Black Streaks, Moss and Lichen: What Biological Growth Means on a Utah Asphalt Roof
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If you look up at a roof in Ogden, Layton, Farmington, or the Salt Lake Valley and see dark vertical streaks, your first guess might be dirt, soot, or “the roof is dying.” Often it is none of those. The Asphalt Roofing Manufacturers Association (ARMA) explains that roof discoloration caused by algae has been observed throughout the United States and Canada, and that Gloeocapsa magma is probably the most prevalent of several algae species that contribute to that discoloration.
GoNano publishes on biological weathering under a post titled The Hidden Eater. The NuRoof Guys hear the same questions about streaks, moss, and lichen on shaded slopes. Here is a Utah-homeowner read of what that growth is and what to check from the ground.
Algae streaks are not the same as moss or dirt
ARMA says algae discoloration usually has a brown to black appearance and may be mistaken for fungus growth, soot, dirt, moss, or tree droppings. The association also notes that algae discolorations should not be confused with moss or tree droppings, which typically produce only localized discoloration.
In plain terms:
- Algae (often Gloeocapsa magma): dark brown-to-black coloring that can look uniform or streaky, and is most visible on lighter shingles.
- Moss: thicker plant growth in damp, shaded pockets.
- Lichen: crusty patches that cling in spots.
- Dirt or granule wash: messy in gutters without the classic vertical streak pattern.
Utah’s Wasatch Front is drier than the Gulf Coast or the Pacific Northwest, so biological growth is less common here than in wet climates. It still shows up on shaded north-facing slopes, lots under big trees in Logan or the Ogden foothills, canyon and bench yards, and valleys that hold leaves or needles. Our earlier note in how to choose asphalt shingles for a Utah roof only said moss and algae are less common here; this post goes deeper on what the growth is and what to do about it.
Why debris and shade matter on asphalt
GoNano’s article page also points out that without regular inspections and cleaning, debris such as leaves, branches, and dirt can trap moisture on the shingle surface, leading to mold growth and water damage, and that clogged gutters can cause water overflow that increases the chance of shingle degradation.
That moisture story fits Utah even when full-blown moss is rare. Needles and leaves in a valley, or shade on a Bountiful or Kaysville north slope, keep shingles damp longer than a sunny Sandy ridge. None of that alone proves the roof has failed.
Strong sun and freeze-thaw still do most of the aging work on Northern Utah asphalt roofs — see why Utah asphalt roofs age faster. Biological growth is an extra factor where shade and debris pile up.
What you can check from the ground (and what to hire out)
Stay off the roof. The NuRoof Guys’ standing advice matches the Utah roof maintenance checklist: look from the ground, use binoculars if you have them, and leave roof-level work to a licensed crew.
From the yard you can often see dark vertical streaks on lighter shingles, thick green or black patches in valleys or under trees, gutters packed with granules or needles, and damp staining under eaves after storms.
Have valleys cleared and gutters cleaned by a pro rather than climbing up yourself, whether it’s a rambler in Centerville or a two-story in Lehi. In the attic, step only on the framing, never on insulation.
Cleaning: soft methods only, professionals preferred
ARMA says: DO NOT use a power washer or any type of brush or broom to clean algae from the roof surface. High-pressure washing systems are likely to damage asphalt roofing and should not be used to remove algae or for any other purpose, such as cleaning other foreign stains or dirt on asphalt roofing.
ARMA also encourages hiring professionals to clean shingles, because the process can make the roof slippery, and recommends that only trained professionals walk, climb, or work on a roof.
ARMA notes that a diluted household-bleach solution may lighten algae discoloration, but only temporarily, and that the discoloration may come back. It also says other cleaning chemicals or methods shouldn’t be used without the shingle manufacturer’s approval, so ask any cleaner to show you the manufacturer’s instructions and check your warranty document first. The NuRoof Guys do not treat every stained roof the same way — sometimes the answer is leave it, clean carefully, repair, restore, or replace.
Repair · Restore · Replace when growth shows up
Streaks alone are not a diagnosis.
- Repair if you have a specific leak, a bad pipe boot, failed flashing, or a few damaged shingles under a wet valley.
- Restore with GoNano roof rejuvenation only when an asphalt roof is dried out and weathered but still sound. Rejuvenation is one step in a maintenance plan, not a way to make an old roof new, and rejuvenation is not right for every roof. Brittle shingles, bare mat, active leaks, or unresolved storm damage need repair or replacement instead. See roof sealing vs. rejuvenation.
- Replace when the roof is worn out. If you are already bidding new shingles, ask about algae-resistant lines for heavily shaded lots; see our shingle selection guide.
After hail or heavy rain, do not assume black streaks are storm damage. Compare what you see with a proper inspection — including after the Layton and Kaysville hail or Tropical Storm Rachel leftovers.
Frequently asked questions
Are black roof streaks dirt? Often no. ARMA says algae discoloration usually looks brown to black and can be mistaken for dirt, soot, or moss.
Is Gloeocapsa magma common in Utah? ARMA says algae growth occurs to varying degrees in all U.S. regions. On the Wasatch Front it shows up most on shaded, debris-holding slopes.
Can I pressure-wash algae off my shingles? No. ARMA says not to use a power washer or brush/broom on asphalt roofing.
Does moss mean I need a new roof? Not by itself. Check the roof’s condition. Failed roofs need repair or replacement; sound but weathered roofs may fit restoration — and rejuvenation is not right for every roof.
Get a free roof inspection
Not sure whether those streaks are algae, moss, storm wear, or something else? The NuRoof Guys will inspect with proper fall protection, photograph what we find, and tell you honestly whether the next step is cleaning guidance, roof repair, GoNano roof restoration, or roof replacement. We work across Utah, mostly in Northern Utah and along the Wasatch Front.
Licensed Utah contractor #14225732-5501. Authorized GoNano installer.
Call 385-383-8479 · Email info@nuroofutah.com · Schedule a free roof inspection
Sources and further reading
- GoNano, The Hidden Eater…
- Asphalt Roofing Manufacturers Association, Algae Discoloration of Roofs
- The NuRoof Guys: how to choose asphalt shingles, Utah roof maintenance checklist, why Utah asphalt roofs age faster, roof sealing vs. rejuvenation