Roofs and flat roofs
What does moss on a roof covering change, and what does it not prove?
Moss holds moisture and can lift tile edges, block gutters and hide the surface. It does not prove the roof needs replacing, and it does not prove the structure is sound. It is a maintenance finding until a surveyor or roofer can see what is underneath.
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?
A thick moss mat stops a surveyor seeing cracks, slipped units and the condition of ridges. The honest comment is that the covering was obscured. Clearing moss is not free of risk: aggressive scraping can break tiles and slates. A roofer should say how they will clear it and what they will inspect afterwards.
Blocked gutters from moss are a separate defect from the covering itself, and they are a common cause of damp walls. Read the rainwater comment alongside the roof comment. There is no official “moss rating”. The condition rating on the element is the surveyor’s judgement.
What should you ask your surveyor?
- How much of the covering could you actually see?
- Are the gutters holding moss, or only the slope?
- Do you want the moss removed before you will comment further?
What are the typical next steps?
- Do not accept a reroof price based only on a green photograph.
- Ask a roofer to clear enough to see, if the purchase depends on the covering.
- Clear gutters are part of the same weatherproofing. Include them in the question.
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
Is moss the same as lichen?
No. Lichen is often a thin crust. Moss is a thicker mat that holds water. The survey should say which it saw if it matters.
Does a north slope always carry more moss?
Often it stays wetter, so growth is more likely. That is not a defect by itself.