Keep moss off asphalt roofs

Maintaining asphalt composition roofs

Asphalt composition roofs are the most common covering in this region. Lifespans range from 20-year 3-tab strip shingles to 25–40 year dimensional architectural shingles and premium lifetime products. Thicker usually means longer lasting; Tim recommends buying the longest lifespan system you can afford and getting multiple contractor bids based on reputation, not price alone.

Treat with zinc — don’t blast the granules

Tim recommends treating asphalt roofs at least twice a year with zinc powder, granules, or solution from a hardware store. Sprinkle product along the ridge; rain dissolves it and washes downslope to kill moss and algae. Wooded or low-slope roofs may need 2–4 treatments a year. Spray solutions with a garden hose or low-pressure sprayer.

Do not pressure wash composition roofs. Granules protect the asphalt from UV. Pressure washing displaces them and can ruin an otherwise good roof. Tim has seen this thousands of times.

Let treated moss release on its own

After treatment, green growth turns brown, then black, then gradually falls away. Brushing risks tearing shingles because moss rhizomes grip the covering. Extremely thick mats can even be the only thing keeping a neglected roof from leaking — Tim often can’t assess those until they’re carefully cleaned.

Real estate timelines sometimes force cleaning for staging, buyer assessment, or insurance. Tim’s take-home point: treat at least twice annually even when you don’t see moss. He treats his own roof four times a year with zinc powder at the ridge; at ten years it still looked brand new.