Hey, Infrared Thermography Can Detect Building Leaks! So, Uh, What Is it?

Probes may still be needed to get a better look at underlying conditions of a roof or a façade, but an infrared survey can help pinpoint where the probes should be taken, minimizing the added cost and time.

How Does It Work?

The science behind infrared thermography is basic: Vibrating molecules generate electromagnetic energy. At higher temperatures, molecules move faster and emit more energy. This energy —  infrared radiation — isn't visible to the human eye, but it can be detected with a camera equipped with an infrared sensor.

Thermal differences appear as different colors in infrared light. By analyzing the color distribution in thermal images, it is possible to locate the areas of a building that are abnormally warm or cool, which may indicate potential defects such as water infiltration, missing insulation, drafty windows and doors, or an inefficient boiler.

Using Infrared to Detect Leaks 

Once water has entered a building, it can travel far and wide, making it difficult to find the sources of the leak and assess the extent of damage. Infrared thermography is particularly useful for detecting water in hard-to-see areas. It can get underneath roofing membranes, go behind walls, and travel inside shafts and conduits. Thermal surveys are also effective for detecting moisture that has worked its way deep below the surface of the roof and saturated the roofing insulation.

Because an infrared survey highlights the thermal differences in building components, it must be conducted under the right conditions. The ideal situation for a roof survey is a clear day, after the sun has heated up the roofing system and any trapped underlying water. As the sun goes down or as the roof is shaded by nearby buildings or structures, the roof cools (what is called radiational cooling), as does moisture under the membrane.

But because water has a high thermal capacity — i.e., it retains heat longer than solids — the trapped water cools much more slowly than the roofing surface. Therefore, in infrared photos taken of a roof that has been heated by the sun all day and then cooled off, thermal differences can be seen between the cooler areas of the roofing surface and the warmer ones where water is underneath the membrane.

Stephen Varone, AIA, and Peter Varsalona, PE, are principals at Rand Engineering & Architecture.

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