Nondestructive Infrared Roof Scans
How to Perform Nondestructive Testing of Roofs for Moisture
Before diving into the specifics of nondestructive testing, it’s good to understand the equipment used to find moisture in low-sloped or flat roofs:
- Nuclear Density Gauges – These gauges count slowed neutrons
- Dielectric Capacitance Meters – These units measure differences in dielectric constants
- Thermal Infrared Cameras – These cameras measure heat differences
Nuclear gauges and capacitance meters are used to conduct spot readings on a square grid space on the roof measuring 5′ x 5′, 10′ x 10′, or 20′ x 20′. Water is located by extrapolating measurements obtained from the gauge. Because the overall sample of the roof is so small, meter surveys are only capable of helping a contractor determine whether the roof is beyond repair.
For this reason, meter surveys are not used to find areas in need of repair, and are primarily useful on roofs that have no gain or loss of solar energy, or for roofs that are not suitable for infrared surveys.
Infrared Thermography for Nondestructive Roof Testing
Thermal infrared testing is far better for finding moisture within the roof because every inch of the roof is surveyed, making it possible to find all area where wet insulation exists. Certain insulation types, and some roofs, do not absorb water, and even if they do they may not exhibit a good infrared signal. This may happen because the roof’s surface is too reflective, or the ballast is too dense.
Roof Infrared Thermal Basics
Infrared imagery is usually a gray-scale image. The various shades of gray represent differences in temperature and emissivity of objects within the image, with lighter objects being warmer and darker objects being cooler, as a general rule.
Because infrared ignores visible light to focus on the infrared spectrum, it is possible to focus on heat emissions instead of visible light. During the day, sunlight radiates energy into the roof and substrate, which is then released during the cooler nighttime hours. Wet areas on the roof will retain this heat longer than dry areas, so infrared imagers are able to detect heat during this window when it unevenly dissipates from the roof.
Images of the roof are taken by an infrared camera and then recorded digitally before being stored on a computer. Images may then be augmented and modified to make it easier to decipher. Often pictures have false color added to increase the visibility of heat differences. Printing these images may also be of use to persons making a report, or drawings based on the data.
Pattern Recognition in Infrared Thermography
The appearance of roof moisture may often be irregular in shape or mottled in appearance. However, these areas are most commonly found in either linear or puddle-like shapes. Linear paths indicate drainage routes, roof edges and seams, or other low areas along the roof. Irregular puddle-like shapes often indicate roof penetrations like standpipes, vents, and drains.
Thermography is the most effective and complete way to find and document wet places in low-sloping and flat roofs, but the ability to conduct an accurate infrared survey is vital to success. One must remember, that no matter how detailed the infrared imagery, it is still not proof that wetness exists in the substrate. This is a non-destructive testing, so core sampling and measuring the moisture content is necessary for verification.