Key Points
- Apply treatment solution and let rain wash away dead moss -- do not scrub or pressure wash
- Pressure washing removes granules and damages shingles
- Zinc or copper strips at the ridge prevent moss growth downslope
- Trim overhanging branches to improve sun exposure and reduce shade
- Algae-resistant shingles contain copper granules to inhibit future growth
Frequently Asked Questions
What is the safest way to clean moss off shingles?
The safest and least damaging approach: apply a commercial moss-killing solution (zinc sulfate or copper sulfate based products) to the affected area, allow it to work over several weeks as rain washes the dead moss away. Do not use high-pressure washing -- pressure washers remove granules and can force water under shingles. Low-pressure washing with moss treatment solution is acceptable for stubborn cases.
Will bleach kill moss on a roof?
Diluted bleach (sodium hypochlorite) is effective at killing algae and moss. A common DIY solution is 1:1 water to household bleach applied with a garden sprayer. Allow to sit for 20-30 minutes, then rinse with a garden hose (not a pressure washer). Bleach can lighten shingle color and, if overused, degrade the asphalt over time. Commercial roof cleaning solutions are formulated to be less harsh while remaining effective.
How do I prevent moss from coming back?
Long-term moss prevention: zinc strips installed at the ridge (rainwater carries zinc compounds downslope, inhibiting growth); keeping overhanging branches trimmed to reduce shade; ensuring gutters are clean so water does not back up; and using algae-resistant shingles that contain copper granules at next replacement. In humid, heavily shaded environments, some moss growth is nearly inevitable and requires periodic treatment.