Roofs and flat roofs
A sedum roof was not walked. What of the waterproofing under the plants is unseen?
The waterproofing under the plants is unseen. A sedum roof carries a living cover over the membrane, the outlets and any protection layer beneath. Not walking it means the survey did not part the plants, check laps, or see whether the membrane is intact. The visit recorded the green cover from where it could be viewed. It has not decided that the waterproofing is sound because the sedum looks even and established from a distance.
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?
Sedum is a planting layer, not the waterproofing. Outlets can sit under foliage, laps can open under the mat, and a protection sheet can hide a split in the membrane. From a ladder or a nearby window the surface can look continuous while those parts stay covered. The survey stopped at the plants. A green roof is often not a surface to walk without a method agreed in advance, and no such opening was made on this visit.
Ask the solicitor for any green-roof guarantee, planting specification or maintenance record, and keep those papers outside the survey. A roofing firm familiar with sedum coverings can inspect the membrane if access is arranged. Do not tell a lender the waterproofing was examined because the plants were visible. The report's limit is the unwalked cover. Outlets and laps under it remain undescribed. A specification is not a substitute for looking under the plants.
What should you ask your surveyor?
- Was the sedum layer left unparted across the roof?
- Which outlets sit under the plants and were not seen?
- Are maintenance records for the green roof outside this visit?
What are the typical next steps?
- Treat the membrane under the sedum as unseen.
- Ask the solicitor for any green-roof guarantee or specification.
- Do not describe the waterproofing as checked from the plants alone.
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
Does even plant growth show the outlets are clear?
No. Even sedum can hide a blocked outlet or a ponding area beneath the mat. The survey did not lift plants to find the outlets and did not run water across the roof. Colour and cover describe the planting. They do not describe the drainage layer or the membrane under it.
Can the edge upstand be judged from the plants in the middle?
Only the edge that was actually in view can be commented on. Plants across the field of the roof do not show the upstand, the perimeter trim or the flashing at the wall. If those edges were not clearly seen, they stay limited. The unwalked centre certainly does not prove them.