A leak in a flat roof can be very hard to find. Water gets through a small hole, then travels under the membrane or through the insulation before it shows inside. The stain on the ceiling can be metres away from the actual fault.
Electronic leak detection, often shortened to ELD, is one way to find the hole itself. This guide explains how it works in general terms, which roofs it suits and how it compares with flood testing.
The basic idea
Most waterproofing membranes don’t conduct electricity. Water does. If there’s a hole in the membrane, water can carry a small electrical current through it to the layer underneath. ELD equipment looks for that path. By tracing where the current goes, the tester can locate a breach, sometimes down to a very small hole.
There are two broad approaches:
- Low-voltage testing. The surface of the membrane is wetted and a low voltage is applied. Probes are used to follow the current to the breach.
- High-voltage testing. Used on a dry, exposed membrane. A brush or wand passes over the surface, and a spark or signal shows where there’s a hole.
Which one suits depends on the membrane and what’s under it.
Which roofs it suits
ELD needs a membrane that doesn’t conduct and, below it, something that does, such as a concrete or metal deck, or a conductive layer built into the roof. Some roofs aren’t suitable without that. For example, some membranes are conductive themselves, and some build-ups have an insulating layer between the membrane and the deck that blocks the current.
Roofs covered with paving, ballast or planting can sometimes be tested, depending on the build-up and the method, but it’s more involved. That’s one reason green and blue roofs can be hard to trace leaks on.
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How it compares with flood testing
Flood testing means blocking the outlets and holding water on the roof for a period to see if it leaks. It can show whether a roof leaks, but not where. It also puts extra weight on the roof, takes time and can make an existing leak worse.
ELD aims to find the location of a breach without flooding the roof. It usually causes little disruption to the building below. It isn’t right for every roof, though, and a flood test is still used in some situations.
What ELD doesn’t tell you
ELD finds breaches in the membrane. It doesn’t tell you the condition of the insulation or deck, how wet the build-up is, or whether the roof as a whole is near the end of its life. For that, a flat roof survey and, where conditions allow, a thermal roof survey give a wider picture. It also doesn’t cover leaks at upstands, rooflights, parapets or walls above the roof unless those details are tested too.
Our electronic leak detection
We offer electronic leak detection on flat roof membranes. The method depends on the roof build-up, so we ask about the roof first and quote for your roof. It’s a test and a report on what we find. Repairs are a separate matter for you and your contractor. If you’re not sure where the water is coming from at all, a roof leak investigation may be the better starting point.
Quick answers
Can ELD test a felt or asphalt roof?
It depends on the build-up and what’s under the membrane. We ask about the roof before quoting so we can say whether it’s suitable.
Does ELD damage the roof?
It’s designed to be non-destructive. Low-voltage testing wets the surface, and high-voltage testing is done on a dry, exposed membrane.
How much does electronic leak detection cost?
It’s quoted for your roof, because the size, access and method vary. Get in touch with details of the roof.
Related services
More advice
- Flat Roof Problems: Ponding, Blisters and Splits
- Why Roof Leaks Are So Hard to Find
- Thermal Imaging on Roofs: What It Can Show
- Green Roofs and Blue Roofs: Inspection Needs
- All advice
This guide is general information about roofs and roof surveys. It isn’t legal, insurance or structural engineering advice; for those, speak to a suitably qualified professional.