Roofs and flat roofs
How should a buyer separate a box gutter, the butterfly roof and a split rainwater head when all three are mentioned together?
Separate the box gutter, the butterfly roof that drains into it, and the split rainwater head at the outlet. The survey has placed three linked parts of one drainage path in one paragraph. It has not decided that the gutter is clear, that both slopes of the butterfly fall correctly, or that the split head still catches the outlet. Each can fail on its own. A visual note of the arrangement is not a water test of the whole path.
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 butterfly roof falls inward, and the channel there is often a box gutter rather than a fascia gutter. A rainwater head is the hopper the outlet should discharge into. If the head is split, water misses the downpipe and runs down the wall. From a window the surveyor may see the head and the outer slopes, and may not see the gutter sole at all. Naming all three explains the layout. It does not clear debris or measure falls.
Ask the solicitor whether the seller has had the box gutter cleared or the head replaced. Those are different jobs. A roofer needs safe access into the butterfly valley, which a home survey does not provide from the street. Do not tell a lender the roof drains because a head is still on the wall. The split is a visible defect at the outlet. The gutter sole may never have been seen.
What should you ask your surveyor?
- How much of the box gutter sole was actually visible?
- What was recorded about the split in the rainwater head?
- Were both inward slopes of the butterfly roof in view?
What are the typical next steps?
- Split the gutter, the roof form and the damaged head.
- Ask when the valley was last cleared.
- Get the head and the gutter looked at from proper access.
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
If the head is replaced, is the box gutter dealt with?
No. A new head catches water that reaches the outlet. It does not clear or reline the box gutter higher up the butterfly valley. The survey did not test that trough. Ask for the gutter as its own item. Replacing the hopper leaves the valley where it was.
Can leaves in the head explain damp inside without a gutter leak?
They can. A blocked or split head dumps water on the wall even when the gutter sole is sound, and a blocked gutter can overflow even when the head is whole. The visit did not sort which of those is happening. Keep both defects open rather than picking one cause.