What is the Right Thermal Scan for My Roof?

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Thermal imaging alone cannot verify the presence of moisture or the leak’s location.

Technicians should use alternative test method such as a moisture meter or a destructive core sample, to confirm the problem. Infrared also cannot find the exact penetration on the roof surface alone.

What a thermal scan CAN do is locate the affected area as defined by the thermal signature seen in the camera. Under the right conditions and with these limitations, an infrared camera can still quickly scan an entire roof for thermal anomalies that indicate possible moisture. Ideal conditions include; bright, sunny days and clear, calm, cool nights. Any ballast or flood coat on the surface must be dry.

Once the timing and conditions are right, managers can opt for one of two types of inspections.

Capacitance-Based Survey

Uses thermal imaging to detect possible moisture due to differences in thermal capacitance between wet and dry insulation in a low-slope roof.

Technicians typically perform this test in warm weather. It relies on the sun and a clear, night sky to create the right conditions. As the sun heats a roof during the day, the surface and the insulating materials beneath it absorb energy. Wet insulation has a higher thermal capacitance than dry insulation, so it absorbs and retains more thermal energy throughout the day. Once the sun sets and the roof’s surface begins to cool via radiational losses, surface areas with dry insulation underneath cool off quickly because less heat is present in this material. Wet insulation has a higher thermal capacitance, so it takes longer to cool because more energy needs to be released for the temperature to change. If conditions are right, areas that are apparently wet stay warmer longer after sunset.

Conduction-Based Survey

Typically done in cold weather, but possible throughout the year. It requires a difference between the indoor and outdoor building temperatures. Wet insulation has a higher thermal conductivity than dry insulation. When the inside of the building is warmer than the air outside, wet insulation transfers more heat out of the building than dry insulation.

As a result, any area of wet insulation appears warmer on the roof surface in cold weather when viewed from the outside. If the temperature difference is reversed, one would look for cold spots instead, indicating a greater amount of thermal energy entering the building at that location.

Although any quantity of trapped moisture in a low-slope roof system can be damaging, the technique works best for insulation that is more absorbent, such as wood fiber, mineral board, and fiberglass. With absorbent insulation, the entire board soaks up water, which can render a far more recognizable and easier to detect thermal pattern.

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