Infrared thermal imaging has been the standard for inspecting flat roofs for years. The typical method, as laid out in ASTM C1153 – 10(2015), describes a 2 to 3-man crew physically walking the roof after sundown with a hand held thermal camera. Using the thermal camera, they search for “hot spots” where the moisture under the roofing material has kept the roof from cooling as fast as the areas of the roof where it is dry. The theory behind the method is sound, but there are several limitations related to the way the data is collected and displayed.
First and foremost is safety. Because the inspections have to take place after sunset, the roof is often dark. Compound that with the fact that the camera operator is concentrating on capturing images, and it is easy to see how any air conditioning, electrical conduit, vent pipes, or plumbing could become tripping hazards. The answer has been to take an extra assistant or two up on the roof with them to make sure they don’t trip or fall off the roof. This does make the process safer, but it is still inherently dangerous, and the added labor will increase costs.
Secondly, the point of view (POV) from a low resolution thermal camera on a 1,000,000 + sq ft roof will give a very limited window of the roof in its entirety. For that reason, it is almost impossible to tell from the photos exactly where or how big the suspected leaking area is. To combat that, the inspection team will usually use spray paint to mark and catalog the area. Again, this works as an okay solution, but it leaves you with a limited ability to see a larger view of the roof to determine the actual size of the leaking area, or the percentage of the roof that has water intrusion. This is a very important data point to know when trying to make an intelligent decision as whether or not to repair or replace a damaged roof!
Another issue presents itself when you dig a little further into infrared thermal imaging theory. Without getting too complicated, the best location to measure the temperature of a surface is at a direct 90-degree angle. When walking on a roof holding a camera forward facing, an inspector is lucky to be at a 45-degree angle, and can easily be at up to a 30-degree angle. When you are trying to measure temperature changes that can be only a few degrees F, this is not ideal.