Infrared Roof Thermography

Infrared roof thermography uses a thermal imaging camera to detect differences in surface temperature on a roof. Wet insulation and substrates have greater thermal mass than dry ones, so after a sunny day they stay warmer longer into the evening and show up as warm patches. ASTM C1153 is the standard practice in North America for locating wet insulation in roofing systems by infrared imaging.

How surveys are done

• Timing: scans are typically made in the evening or at night after a clear, sunny day that has warmed the roof, with the roof surface dry.
• Weather: low wind, no rain and no standing water or dew on the surface; heavy cloud cover overnight can reduce contrast.
• Platforms: handheld cameras on the roof, or images taken from aircraft or drones over large areas.
• Marking: anomalies are outlined on the roof surface with paint or recorded on a roof plan.
• Verification: suspect areas are confirmed with core cuts or other moisture tests.

Where it works best

Infrared surveys are most effective on low-slope roofs with absorbent insulation, such as perlite, fibreboard and fibreglass, directly under the membrane. They are less reliable on roofs with heavy ballast or pavers, roofs with reflective surfaces that make readings harder to interpret, very thick or closed-cell insulation that absorbs little water, and roofs where the heat source is mainly from inside the building.

Limits

An infrared camera does not see water. It sees surface temperature differences, which can also come from variations in surfacing, extra layers of membrane, patches, flashings, rooftop equipment, reflections and differing insulation thicknesses. Professional guidance stresses that thermographers should be trained and that all anomalies need confirmation. A survey that skips verification can lead to unnecessary removal of dry material, or miss wet areas.

Other uses

Thermal imaging also helps find air leaks, missing insulation and heat loss in attics and buildings, and some fire safety practices propose thermal cameras for checking for hidden hot spots after torch-applied roofing.