The short answer
Moss does not automatically mean a roof needs cleaning. Start by asking whether it is obstructing drainage or whether another defect needs a roofer's assessment.
Ask what problem the work will solve
Describe blocked outlets, gutter overflow or material falling from the roof separately from a desire for a cleaner appearance. A contractor should explain what they have observed and why the proposed work is appropriate. If the concern is a leak, broken tile or deterioration, cleaning is not a substitute for diagnosing and repairing that problem.
Why the method matters
The National Federation of Roofing Contractors cautions that aggressive removal techniques and unnecessary traffic on the roof can damage tiles. Its advice is to seek a reputable roofing contractor's assessment. That is a reason to question a blanket promise to clean every roof using the same process, not a reason to prescribe a different treatment without inspecting the covering.
Prepare a useful enquiry
Take photographs from the ground showing the roof slopes and any affected gutter or outlet. Mention the roof covering if known, previous repairs and access around the house. Flag a conservatory or extension beneath the work. Leave close inspection and the access plan to the provider.
Read the full scope
Ask whether the quote includes collecting debris, checking gutters afterwards, protecting surrounding surfaces and any follow-up. If coating or treatment is proposed, ask why it is needed and what evidence supports the promised result. Cleaning, repairs and coatings should be separately understandable decisions.
Do not book a universal cleaning interval
Roof condition and drainage concerns are a better starting point than a fixed recurring wash. Keep a record of assessments and agreed work. A provider should be able to explain the reason for any recommended return visit.
Sources & further reading
Sources checked 2026-09-13. Statistics retain their original reference year.