Not every roof leak needs sophisticated equipment. Some of them can be found with a torch, a good eye, and twenty years of knowing what to look for.
But some of them need a process. And getting the process wrong — going straight to complex testing when the answer is sitting in a perimeter detail, or doing a visual inspection when the waterproofing is buried under a metre of growing media — wastes time and money.
Here is how a competent investigation actually works.
Step 1: Start with the common suspects
Before any equipment comes out, look at the obvious areas of weakness. Not because it is lazy — but because that is where most failures are.
Terminations are the first thing. This is where the roof stops: the membrane returns up the wall, minimum 150mm, and the top of that upstand needs to be sealed. If that sealant has broken down — and it does, especially on unmaintained roofs — water gets behind the waterproofing system. Not through the field sheet. Behind it.
Penetrations are next. Any point where something passes through the deck — a pipe, a drain, an outlet, a service — is a potential point of weakness. Look at how they have been dressed. Look at whether they have been maintained.
Cover flashings and cappings. Copings. The areas that are not glamorous but are disproportionately responsible for water ingress.
Take a project we looked at recently: an inverted hot-melt roof that had leaked twice in its history. The temptation is to go straight to the field sheet — buried leak detection, flood testing. But that roof had been sitting with ballast on it and had probably been subject to wind-driven rain at a specific location. The answer was almost certainly in the perimeter detail, not the membrane itself.
Good investigation starts with eliminating the likely causes before committing to complex testing.
Step 2: Consider the build-up before choosing a method
Once the visual has not resolved it, the choice of testing method depends on what you are dealing with.
Wet electrode testing works brilliantly on accessible membranes in wet conditions. High-voltage dry testing works on dry, non-conductive membranes on conductive substrates. Neither works through a green roof system with 300mm of growing medium on top.
For buried waterproofing — green roofs, blue roofs, hard landscaping, ballasted systems — the only viable non-destructive option is buried leak location using electrical field mapping. Vector partners with Texplor Group for this. The technology locates membrane breaches to within approximately one metre without lifting a single plant or paving slab.
If the roof is non-conductive and the waterproofing is accessible, moisture mapping with the Tramex Dec Scanner is the alternative route: scan the whole area in a grid pattern, identify where moisture is sitting in the build-up, and then focus the investigation on those areas.
Step 3: Think about the design — not just the membrane
When reviewing a roof design — particularly at tender stage where a contractor is picking up design responsibility — the question is not just whether the membrane has been correctly specified. It is whether the design has created conditions that will cause failure.
Falls are an obvious one. Not just falls across the field sheet — falls in gutters and valleys, falls to outlets, falls that prevent standing water from sitting against the membrane long enough to find its way through. Some bituminous products and single-plies are vulnerable to algae build-up in standing water — what is called mud curling, where algae attacks the surface layer and it starts to peel back.
Door thresholds are a consistent problem. A designer specifies 150mm of insulation — correct. But they have not allowed another 150mm to the top of the door threshold. The upstand ends up at 20mm. That failure is designed in before the contractor puts anything on site.
Outlets in localised sumps where the membrane has to dress around the outlet and ends up raised. Overflows that are missing entirely. Insulation flotation risk in blue roof configurations. These are the design details that experienced eyes catch at Stage 3, not after handover. That is what the Vector Design Review service is for.
Step 4: Do not trust what has already been done
This is perhaps the most important discipline in investigation. Someone tells you they have already had it looked at, already done repairs in a certain area, already ruled something out. That may be completely accurate. It is also frequently wrong.
We start from scratch. We repeat tests that other people have done, because we know how we have done them. We do not rule out an area because someone says they have repaired it — we check the repair. We have never yet trusted a previous repair until we have verified it, and we have never regretted that approach.
What experience actually buys you
Andy Flood has spent his career in flat roofing — his father was a flat roofing contractor, and Andy has worked at every level of installation and inspection since. He knows before he gets on site which details are likely to have failed on a given roof type.
Ben brings authorship on CIRIA C817 and BS 8102:2022, expert witness experience, and the technical depth that comes from having reviewed and written the standards that govern how these investigations should be conducted.
Together: we know where defects occur before we arrive on site. We have the equipment to find them when they are hidden. And we know how to explain what we find in a way that leads to a defined, proportionate repair — not a speculative re-roof.
Talk through your investigation | Buried leak location for complex roofs