Treatment is not removal
A moss treatment kills living moss so it can be brushed or blown off. OSU Extension is clear that you must still remove the dead material. Skipping that step leaves a brown mat that keeps holding water against the shingles.
Common treatment types
| Type | How it works | Things to know |
|---|---|---|
| Potassium salts of fatty acids (soap-based) | OSU describes them as biodegradable products that damage moss cell membranes so the moss dies | Short-acting, so they do not prevent regrowth |
| Zinc sulfate and similar zinc products | Kills moss on contact and is widely used by roof cleaners | Zinc runoff can harm aquatic life, so manage where it drains |
| Zinc or copper strips | Release metal ions along the roof as rain runs over them | Preventive, not a cleaner. Installation can cause leaks if done badly |
Why treatments wash off
Per OSU, moss killers are short-acting: the next rain washes them off, and they provide little long-term control. Treatment is a reset, not a permanent fix. To slow regrowth you have to change the conditions, mainly light and moisture. See moss prevention.
Timing
Treat when moss is actively growing, then give it a dry spell to work. In the Salem area that usually means early spring or early fall. See when to treat.
What a professional adds
- Application at low pressure so shingles stay intact
- Safe roof access, which matters on a wet, mossy slope
- Removal of the dead moss and clearing of gutters
- A preventive step and, ideally, a written guarantee
Ask what product will be used, how runoff is handled near plants and drains, and whether the company holds any licenses that apply. See how to hire.
Not sure which treatment fits your roof? Request a free quote and ask the company to explain.