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Pressure washing works well for most roofs, but you'll want to be careful about the angle and pressure to avoid damaging shingles - are you dealing with asphalt shingles or something else, and how steep is your roof? For a gentler ongoing approach, zinc or copper strips installed along the ridge will kill off moss and algae over time as rain washes the metals down.
Sarah Baker asker
Asphalt shingles, pretty steep pitch. Thanks for the tip about the metal strips!
Start with zinc or copper strips along the ridge - they're the real long-term solution nobody mentions enough. As oxidized metal washes down the roof with rain, it kills moss and algae spores before they get a foothold. Install them now and you're basically done thinking about this for years. Much gentler than any cleaning method, and it prevents regrowth rather than just treating what's already there.
If you do decide to clean first, the pitfall everyone glosses over is that high pressure will absolutely shorten your shingle lifespan, especially on rural roofs where weather's already beating them up. Low-pressure wash (under 1500 psi) with a biodegradable algaecide or copper sulfate solution works way better than blasting. Let the chemical sit for 15-20 minutes, then rinse gently. You're dissolving the growth, not jackhammering it off.
For a rural property, timing matters too - do this work in spring or early summer so the moss and algae are actively growing and more susceptible to treatment. Avoid late fall when everything's dormant and the chemicals won't work as well. And honestly, if your roof gets hammered by shade and moisture, those zinc strips really are worth every penny. I've seen roofs stay clean for a decade with just that one intervention.
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