Shingle Problems
Why is there moss and algae on my roof?
Short answer
Black streaking is an algae that feeds on limestone filler in the shingle; moss takes hold where shade and moisture linger, typically north slopes and under trees. Algae is mostly cosmetic, but moss holds water against the shingle and lifts the courses, which does cause damage.
Two different problems
Gloeocapsa magma — the black streaking — is unsightly and slightly reduces reflectivity, but it isn't structurally destructive. Moss is different: it holds moisture in place through freeze-thaw cycles and physically wedges under the shingle edge, which in Maine is a genuine path to damage.
Removing it without doing harm
- Never pressure wash — it strips granules and forces water under courses
- Use a low-pressure application of an appropriate cleaning solution
- Protect plantings below and rinse gently
- Trim back overhanging limbs so slopes dry out
- Consider zinc or copper strips near the ridge to slow regrowth
Clean before treating
Organic growth has to come off before any rejuvenation treatment goes on — a treatment can't be absorbed through a mat of moss. Cleaning is part of the prep on roofs that need it, and it's included in the scope we write up.
See if your roof qualifies
Six quick questions about your roof, and an honest read on whether rejuvenation is likely to be a fit for it.
2-minute self-check
Answer six questions from the ground.
This won't replace an on-roof inspection, but your answers shape the recommendation you'll get at the end — including when rejuvenation isn't the right call. "Not sure" is a fine answer.
1.Is your roof roughly 8–25 years old?
2.Do you have any active leaks or interior water stains?
3.Are there shingles missing, cracked through, or hard-curled in sections?
4.Do you see granules collecting in gutters, or fading and dry-looking shingles?
5.Do any roof planes sag, or does the decking feel soft?
6.Does the roof have more than one layer of shingles?
0 of 6 answered — your personalized result appears when you finish.
Before you replace — see if you qualify.
A free roof assessment tells you whether your asphalt shingles still have serviceable life. If they don't, we'll say so and point you to a roofer we trust.