Nuclear surveying is an ideal tool to use on roof systems that are unable to be scanned with an infrared unit. A ballasted rubber roof that is designed with heavy river rock to hold down the membrane is a perfect example where nuclear surveying can be used. PRSI uses a special roof gauge made by Troxler. The unit reads the hydrogen count underneath the membrane, through a backscatter technique, therefore allowing us to determine what areas of the roof are wet.