It’s a phone call that every architect dreads. A client, who recently settled into a new space, calls to coolly inform you that water is leaking into the building. And the attorneys are on standby.
Besides building consultants, designers can turn to another resource to help fix the leak: thermal imaging. “Thermography is a way to scan a building façade or envelope and find critical areas quickly or directly,” says David Felleti, a specialist in the Northbrook, Ill., office of building consulting firm Wiss, Janney, Elstner Associates (WJE).
The germanium lens on a thermal-imaging camera captures wavelengths in the infrared spectrum, which nearly all objects radiate. A wavelength’s intensity depends on the object’s temperature and surface emissivity; reflective materials such as metal have a low emissivity.
Though thermal imagers can be purchased at department stores, interpreting the output accurately is not so straightforward. Even training programs for budding thermographers—who can earn Level I (beginner) to Level III certification from training centers that comply with the American Society for Nondestructive Testing guidelines—typically do not cover how to apply thermography to building science, says Scott Wood, president of Scott Wood Associates in Gig Harbor, Wash., and a Level III thermographer. “Because thermal images can be convoluting with the different patterns, you have to understand what you’re seeing and why. You need to understand heat flow and moisture patterns.”
Through the colorful heat maps captured in thermal imagers, thermographers can identify building defects such as insulation gaps, thermal bridging, and trapped water—or, more specifically, evaporative cooling and the thermal capacitance of water. Thermography can also detect airflow when the air—at a different temperature than the ambient temperature—blows across a surface, Wood says. Blower doors or the building’s mechanical system are often used to create negative pressure in the investigated area, forcing air movement through the building envelope.
Thermal imagers do have their limitations. Cameras require a temperature differential, typically of about 10 C, to see thermal patterns. This difference is also the minimum required by standards such as the Residential Energy Services Network (RESNET) Interim Guidelines for Thermographic Inspections of Buildings.
Though some newer cameras have sensitivities between 2 C and 5 C, they still “can’t see through walls,” Wood says. Imagers detect only shallow, subsurface conditions, so thermal imaging cannot detect bodies inside buildings or mold inside walls.
Thermographers must consider these limitations for projects with metal cladding and roofs, glass curtainwalls, or unpainted, corrugated roof decks. Materials that hold moisture, such as ballast stones, can also influence whether thermographers take images from the inside or outside, Felleti says.
Beyond knowing likely areas of construction defects, air and water infiltration, and insulation gaps—roofs, walls, windows, doors, construction joints, and such—thermographers must also time their investigations strategically. Thermography is best done in the morning or at night, says Pasi Miettinen, president and CEO of thermal-imaging provider Sagewell in Woburn, Mass.
Felleti also prefers the later shift. “I don’t like to shoot in morning because the dew gives a skim of water across the roof,” he says. “You want the building to heat up [during the day]. Any water under a roofing membrane will stay warmer longer, so once the top surface cools down, you can pick up the image” of the warm aberration under the roof membrane. Winter thermal imaging is also preferable because the extreme temperature differentials between the indoors and outdoors help to distinguish results. Precipitation and wind are other environmental considerations.
Turn the page to read the rest of the story, and see a high-tech thermal imaging video from Sagewell.