W. CONSHOHOCKEN, Pa. — Excess moisture trapped in roofing or waterproofing systems can adversely affect performance, as well as lead to premature failure of a system and its components. Using an electrical impedance scanner is a fast and relatively easy way to conduct moisture surveys of roofing and waterproofing systems.

A new ASTM International standard covers the use of electrical impedance scanners to monitor the moisture level of a roofing system over various stages of its lifespan. That standard is ASTM D7954/D7954M, Practice for Moisture Surveying of Roofing and Waterproofing Systems Using Non-Destructive Electrical Impedance Scanners.

“As the practice of using electrical impedance scanners to locate moisture and evaluate the comparative moisture levels within roofing and waterproofing systems is widely used, it is important to have an ASTM standard in place that would qualify the types of moisture scanner suitable for this purpose,” says ASTM member Sean Fallon, Sean Fallon Consulting.

Fallon notes that the new standard gives guidelines for moisture scanners, how they should be used and on which roofing systems scanners are most effective. In the described procedure, an electrical impedance scanner is moved across a roof surface. Low frequency signals are transmitted non-destructively through the surface, measuring the electrical alternating current impedance. The strength of the signal varies in proportion to the moisture level under the footprint of the scanner, with greater amounts of moisture resulting in higher comparative moisture readings.

ASTM D7954/D7954M can be used at the following points in the life cycle of a roofing/waterproofing system:

During or at completion of installation of a system, to determine whether there was moisture intrusion into the system or materials;

At regular intervals as part of a preventive maintenance program; and

Before reroofing or repair work, to assist in determining the extent of work and replacement materials.  

ASTM D7954/D7954M was developed by Subcommittee D08.20 on Roofing Membrane Systems, part of ASTM International Committee D08 on Roofing and Waterproofing. All interested parties are welcome to participate in the ongoing standards development activities of D08.20. 

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