Electronic Leak Detection (ELD)

Electronic leak detection (ELD) locates holes, splits and seam defects in roof and waterproofing membranes by detecting electrical current passing through the breach. Most roofing membranes are electrical insulators, while the deck or a conductive layer beneath is a conductor. Where the membrane is breached, current can flow through the opening, and instruments detect that path. ASTM D7877 describes electronic methods for locating leaks in waterproof membranes, and ELD is widely used to test new roofs, green roofs, plaza decks and below-grade waterproofing.

Low-voltage methods

Low-voltage methods (around 48 volts or less) need a wet membrane surface, so that a continuous film of water carries current to any breach.

• Vector mapping (electric field vector mapping): a perimeter wire around the test area is energised, and a technician uses a pair of probes to follow the voltage gradient in the water to the breach.
• Scanning platforms: a wheeled unit with conductive brushes is pushed across the wetted membrane and signals when it crosses a breach.
• Vertical surface scanning: a moistened sensor checks walls, parapets, corners and flashings.

High-voltage method

High-voltage testing (typically 600 volts or more) is performed on a dry membrane. A brush or wand electrode is swept over the surface, and a spark jumps through any breach to the grounded substrate, triggering an alarm. The test voltage is set according to membrane thickness.

Requirements

• A conductive path beneath the membrane. Concrete decks often provide this. Over insulation, a conductive layer, such as a scrim, screen or conductive primer installed under the membrane, is needed. Many roofs are designed with ELD in mind from the start.
• Non-conductive membranes. Some methods cannot be used on conductive membranes such as black EPDM or heavy carbon-black materials; high-voltage testing is limited to non-conductive membranes.
• Isolation of grounded items such as drains and metal penetrations to avoid false readings.
• Skilled operators: results depend heavily on technician experience.

Advantages and limits

ELD can find breaches as small as pinholes and can be repeated after repairs, unlike flood testing, which IIBEC material describes as often inconclusive. Overburden such as insulation, drainage mats, root barriers and soil in protected or vegetated roofs can interfere with signals or shift apparent leak locations, which is why permanent leak detection grids are sometimes installed under green roofs.