Thermal imaging (also known as thermography) is the process of using an infrared camera to detect electromagnetic waves in the infrared spectrum. These infrared waves are heat that radiates from everything in our physical world and they are not visible with the human eye. Thermal imaging is a great technology with many applications, however it's not a magic ball.
Critics point to untrained inspectors, proliferation of inexpensive, low-resolution cameras, and dependence on environmental conditions to question the value of infrared technology for use in home inspections. Training and equipment are valid concerns that inspection clients should consider when hiring an inspector, and nderstanding how infrared cameras work and their limitations can help us to determine where they provide value during a home inspection.
In photography we create an image with visible light, but with thermography we create an image with thermal radiation, otherwise known as heat. In building science, the relative temperatures of building materials can tell us about how they are performing. Thermography, however, is not without its challenges. Temperature differential, like contrast in photography, is critical to good results when taking thermal images. The two photos below illustrate this point. The photo on the right has very low contrast, making it difficult to see details.
How We Use Thermal Imaging In Home Inspections
In thermal imaging, a lack of temperature differential makes it difficult to see details. A good rule of thumb for building science in thermography is a temperature differential of >20 degrees for optimal results. This is not a hard and fast rule however, as there are some instances where good results can be achieved with less temperature differential. Below are two good examples:
In the first image we see sloughing insulation in a wall cavities within a bedroom. This condition is not visible without an infrared camera and its commont to many homes, both old and new. The second image is air infiltration at an intersection of a first floor ceiling and the exterior wall following a renovation. Both of these images were taken on a day with an overall temperature differential of less than 10 degrees (internal temperature of 70.4 degrees and an outside temperature of 63.8 degrees). Because the thermal gradients in both images are common to these conditions, interpreting the images was possible, even though we were well below the >20 degree differential.
Sloughing insulation in walls
Air infiltration at corner of wall and ceiling.