Roofs and flat roofs
What should you ask if moss is sitting in a hidden gutter rather than on the tiles?
Ask which gutter, and whether it can still discharge. Moss in a hidden gutter, a secret gutter or a valley trough is a blockage in the channel, not the same comment as moss on the tiles, and moss on the covering does not prove the gutter is blocked. From the ground a hidden channel is often unseen.
Last reviewed 24 October 2026. Written for buyers in England and Wales unless this answer says otherwise. No named surveyor has signed this page. It is general guidance, not a report on your house, and not legal advice.
What is the fuller explanation?
Moss holds moisture and silt. In a channel you cannot see from the pavement it builds a dam, the outlet blocks, and water overtops into the roof or the wall. The tiles above can be clean or they can be green. Those are two observations. A home survey should not use a green slope as a substitute for looking at a gutter it could not see, and it should not ignore moss it did see in a hopper or an open valley.
Clearing moss from a hidden gutter needs safe access. There is no standard price, and it is not a re-roof. If the lining under the moss is split, that is a second finding the survey may not have reached. Ask the roofer to clear and then report the lining, rather than to quote a new covering because a photograph shows green tiles. Do not scrape a gutter from a bedroom window.
What should you ask your surveyor?
- Did you see moss in a gutter, on the covering, or both?
- Which gutters were hidden?
- Is the outlet itself blocked, or only the channel?
What are the typical next steps?
- Tell the roofer to look in the hidden channel, not only to brush the tiles.
- Do not treat moss on slates as proof the secret gutter is full, or empty.
- After a clearance, ask whether the lining underneath was intact.
Costs vary with the building and with who you instruct. Where this page does not cite a published figure, ask the surveyor, a relevant specialist, or your solicitor for a written quote. Do not treat a forum average as the price.
Also asked about this
Should moss on tiles always be removed?
The survey can note it. Removal is a maintenance choice and can damage slates if it is brutal. It is not this gutter question.
Is moss in a hopper the same?
A hopper is a visible collector. Moss there is a blockage you can often see. A hidden gutter is the one the pavement view misses.