The moss makes the roof look older than the house feels. A pressure washer promises a dramatic before-and-after photograph. The part missing from that photograph may be protective shingle granules.
Cleaning can cause the damage you hoped to prevent
IKO's moss-removal guidance warns against pressure washing and aggressive removal methods. Ask a qualified roofer to distinguish the growth from other staining and assess shingle condition. A clean-looking surface is not the only measure of a successful treatment.
Consider why that roof area stays damp
Review debris accumulation, overhanging vegetation, and drainage as part of maintenance. Any tree work needs appropriate expertise and local permission where required. Obtain the proposed cleaner and method in writing, including protection of nearby plants and surfaces. Ask what the roof should look like immediately afterward and what may take time to change. That expectation matters: trying to remove every trace in one visit can encourage exactly the scraping or blasting the shingles shouldn't receive. Agree on the follow-up observation from the ground before the crew leaves. Stay on the ground rather than climbing onto a wet or mossy roof.
Before the next step
- Identify the growth and condition before choosing treatment.
- Check the roof manufacturer's approved cleaning approach.
- Arrange safe access and review the causes of persistent dampness.
Ask what improvement to expect now and what will take time, then leave the roof to the approved treatment. A slower change in appearance is easier to accept when you've agreed on it before the cleaning starts.