Remove the moss.
Keep the roof intact.

First, make sure it is moss.

Moss is raised growth, often found where a surface stays damp and shaded. Algae and lichens can look different and call for different decisions. Ask the provider to identify what is present rather than treating all discoloration as the same problem.

Moss can slow drainage and contribute to shingle damage. That calls for an appropriate plan, not an aggressive promise to leave every roof spotless in one visit. OSU identification and risk guide

Three parts of a moss proposal

1. Physical removal

   What growth will the crew remove, and how will it avoid damaging the roof? Ask how heavily attached patches and fragile areas will be handled. “Remove everything immediately” is not a useful guarantee without a material-specific method.

2. Treatment

   Will a product be applied, and what is it intended to do? Ask for the product name, label directions, roof compatibility, plant protection and runoff plan. Treatment and the disappearance of visible material are not necessarily simultaneous.

3. Follow-up & prevention

   What should you expect after the visit, when will the provider reassess the roof, and is that included? Maintenance can address retained debris and conditions that favor regrowth. Ask what any warranty actually covers and excludes.

Protect the shingles and the surroundings.

For composite/asphalt shingles, OSU advises against high-pressure devices because they can remove protective granules. Do not use a driveway-cleaning method as the default roof-cleaning method. Follow the actual roofing product’s care instructions. OSU roof-moss precautions

Before treatment, ask how the crew will protect landscaping, adjacent surfaces, people and pets, and what happens to runoff from gutters and downspouts. Do not assume that “biodegradable” means a cleaner belongs in a storm drain.

What should you expect after treatment?

Ask the provider to describe the appearance on departure and the expected change afterward. Some services leave treated material to loosen over time; others include more physical removal. The timing depends on the process and roof. Get the provider’s own timeframe in writing instead of relying on a universal number of days.

Agree on follow-up photos, cleanup of material that reaches gutters or the ground, and when you should contact the provider if the result differs from the quote. Do not mistake a service’s marketing warranty for a warranty from your roof manufacturer.

Make regrowth a maintenance question.

Discuss retained leaves, shade and persistent moisture. Where tree work is appropriate, treat it as a separate job and check any applicable permissions. A fixed annual treatment is not automatically right for every roof; choose an inspection and care plan based on the actual condition.