Thermography is almost magic when it comes to finding problems with insulation in buildings. Whether you are auditing a building, providing consulting services, doing work on it, or overseeing work for quality control purposes, thermography—used properly—is a powerful tool that pays great returns.
Remember, we can’t see into or through walls, but we do see the thermal signatures on the building surfaces. When there is a temperature difference across the building envelope, heat moves differently depending on how effective the insulation is. Typically, an 18°F difference in temperature between the inside and outside of an exterior wall will allow us to see thermal patterns related to missing, damaged or poorly performing insulation.
To “read” the thermal image, compare everything to the known value of the framing member. Framing is not a very good insulator, so depending on the direction of heat flow, it is easy to compare the cavity between the framing to see if it is insulated or not. Sounds simple? It often is—but not always!
Now get ready for some logistics! If it is colder outside, heat is usually flowing out of the building. A 4” thick wall stud will conduct more heat than an insulated wall. As a result, it appears cooler than the wall. With summer conditions, heat normally moves into the building. That same framing member, viewed from inside, will appear warmer. Cavities that are not insulated conduct heat at a greater rate—in either direction—than the framing.
It is important to know what kind of insulation is in a cavity. Each will have a characteristic “signature” and some may require special conditions to gain optimum results. Many buildings are either partially insulated or just plain poorly insulated, so expect to see many different patterns!
It is always valuable to follow the insulation inspection with a blower door test that shows how the material performs under pressure. While a blower door test creates an artificial situation, it does mimic the real pressure gradient buildings face most of the time. Many types of insulation, especially fiberglass, simply do not perform well in these circumstances. But we’ll talk more about the blower door later—stay tuned for Part 2 next Wednesday!
John Snell—The Snell Group, a Fluke Thermal Imaging Blog content partner