Infrared flat roof inspections work on the principal that different construction materials have different thermal mass. In the daytime the sun heats the structures. After the sun sets the structure begins to cool. If there is a leak or moisture, the insulation and materials of the structure will become wet. The wet materials have a higher thermal mass than the rest of the “dry” structure. As a result of this difference the “wet” areas will maintain heat energy longer than other areas providing the infrared inspector with a clear picture of the damaged area. The temperature difference between damaged and “dry” area is typically very small (2-4 degrees.)
A building inspection is either an interior or exterior survey. The thermographer decides which method would give the best results under certain weather conditions. Interior scans are more common, because warm air escaping from a building does not always move through the walls in a straight line. Heat loss detected in one area of the outside wall might originate at some other location on the inside of the wall. Also, it is harder to detect temperature differences on the outside surface of the building during windy weather. Because of this difficulty, interior surveys are generally more accurate because they benefit from reduced air movement.