Laboratory Tests of Cable-Based Roof Moisture Detection System

The writers have devised a prototype cable-based roof moisture detection and location system (U.S. Patent 5,648,724) that was tested in simulated conditions. The detection system can use a variety of principles to monitor roofing for the presence of moisture. The location system uses a metallic time-domain reflectometer (MTDR) to locate a suspected wet area by sending an electromagnetic pulse or step signal down the sensor cable and looking for reflections caused by a change in the dielectric constant surrounding the cable due to the presence of a wet area. Tests revealed the MTDR technique to be sensitive and able to locate the position of less than 1 L (0.22 gal.) of water within 0.3 m (1 ft) over 30.5 m (100 ft) of cable. Where multiple regions of wetting were present along the length of the cable, it was possible to locate each boundary between wet and dry.