For building surveyors

You triage. We locate.

A building surveyor is expected to know everything and cannot be a specialist in everything. On a buried-membrane roof, the most valuable thing you can do is recognise the case that needs a specialist, and instruct the right one.

Talk to Vector

By Ben Hickman, Technical Director · 8 October 2026 · Updated 8 October 2026
Contributing author, CIRIA C817 (Blue Roofs) · contributing committee member, BS 8102:2022 revision

Your situation

You have been instructed by an owner, an insurer, a managing agent or a solicitor to report on a roof that is leaking. The roof is a green roof, a podium deck, an inverted roof or a blue roof, so the waterproofing cannot be seen. A roofer has probably already looked, possibly patched, and the roof still leaks. You have to advise on cause, on method and on who to instruct, and you may have to defend that advice later.

Vector is an independent consultancy that locates defects in buried waterproofing membranes through the build-up, without stripping the roof, and then witnesses the opening-up, the repair and its verification. We are not a roofer and we do not sell membranes or sensors. We are the sub-consultant you instruct when the membrane cannot be reached.

What goes wrong in the instruction

The commonest error is specifying or tendering with the wrong party in mind. A complex green roof leak investigation is a niche professional service; very few firms do it, and a roofing contractor tendering against a method statement for "leak detection" will offer a visual inspection and exposure, which is what has already failed.

The second is treating the scope as fixed before the information is in. The scope should be collaborative: what you can provide as context decides what we can quote and how quickly. The third is leaving the opening-up and inspection to the roofer once the location is known. That is where the certainty is lost, and it is the step your client will be relying on in any later dispute.

What to send with the instruction

Roof plan with the points of ingress marked, and the pattern of ingress (during rain, hours after, first occurrence or repeat)
As-built details and O&M information, so the build-up is known before anyone visits
Maintenance record, including previous leaks, previous repairs and who carried them out
Photographs of the ingress and of the roof surface
Who is responsible for the roof, who occupies beneath it, and whether written permissions for access and for recreating the leak are in place

With that, we carry out a desktop review and tell you whether a Buried Leak Location survey is viable for this build-up before anything is quoted. Multiple waterproofing layers, slip layers and some vapour control layers can make the survey ineffective; we would rather say so first.

What the survey involves

The roof has to be leaking while it is measured. The facilities team recreates the leak by watering the deck, with our guidance, and we attend once it is running: two of the Vector team, usually for two consecutive days, measuring across the surface in a grid through the planting and substrate. Planting does not normally need to be moved.

In plain words, the survey maps the flow of electricity through the roof from an electrical source at the point of ingress. The outcome is a contour map of the roof plan showing where conductivity is greatest, which corresponds well with the points of ingress. The breach shows as a clear anomaly at a highly localised position.

What you receive

A professional report, typically two weeks after the site days, with the contour map of leak locations and suspicious areas on the roof plan
A call to talk it through and agree where localised opening-up will be carried out, typically a minimum of about a square metre per location so that a proper repair is possible
Attendance on exposure to investigate, identify the point of ingress and carry out quality assurance on the remedial works
A statement of independence: no installer relationships, no membrane or sensor manufacturer to sell

The report is written for the owner or main contractor and is equally usable by a latent defect insurer. Location evidence of this kind has been relied on by an expert witness in a legal case, and our Dutch partners see the method used routinely in disputes. Vector's Technical Director also acts as an expert witness in waterproofing matters, so the report is written knowing what it may later have to withstand.

Suggested wording for your instruction

"Desktop review of the roof build-up and ingress record to confirm viability of a Buried Leak Location survey; if viable, survey of the waterproofing membrane through the build-up to locate points of ingress and plot them on the roof plan; report with contour map and recommended opening-up areas; attendance on exposure to confirm the defect and witness the repair; verification of the repair." Send us the drawings and we will refine it with you.

Instructing on a buried-membrane roof?

Send the roof plan and the ingress record. We will tell you whether a survey is viable before we quote.