Roofs and flat roofs
What is a hopper head, and why does an overflowing one matter?
A hopper is the open box that collects a small gutter or a balcony outlet and passes it to a downpipe. If it is blocked or split, water pours down the wall at that point. The survey can see staining even on a dry day. It has not water-tested the hopper, and overflow is not a flood-map category.
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?
Hoppers sit on flat-roof outlets, bay roofs and valley ends. A stain below a hopper with a dry main eaves gutter means the defect is local. Replacing the whole eaves trough will not clear a blocked hopper on a rear addition. The surveyor should locate it. If they could not see it from the ground, they should say so.
Clearing a hopper is sometimes a few minutes and sometimes a split casting that needs a scaffold. The survey cannot tell those apart without access. There is no published national price. If the rating says the wall is being damaged, get a quote that names this hopper before legal commitment, which is what RICS asks for when a rating 3 repair is the issue.
What should you ask your surveyor?
- Which hopper, and which wall does it wet?
- Could you see into it, or only the stain?
- Is the main eaves gutter a separate comment?
What are the typical next steps?
- Photograph the stain and the hopper from the ground.
- Do not price a whole new rainwater system for one blocked box until a roofer has said the rest has failed.
- Keep this distinct from any flood-risk search. One is a fitting. The other is a map.
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 a hopper a soil pipe?
No. A soil pipe takes foul water. A hopper takes rainwater. Mixing them is a drainage defect, not a definition.
Can ivy be the blockage?
It can. The survey may say the hopper was hidden by growth. Hidden is not the same as tested.