​

Roof Maintenance in General has waterproofing problems that manifest themselves in two ways: Leakage and entrained moisture contamination. Leakage is pretty simple, although the leak inside the building rarely directly relates to the exact spot on the roof, since the water flows down the slope of the roof to a spot that is not sealed and into the building at that point. Most leaks occur where the waterproofing is sealed or where there is a penetration of the roof. Since most types of roof systems absorb some amount of water, it is harder to find the exact spot of water contamination in the insulation because it may not leak into the building until it has absorbed all the water it can hold.

 

There are three types of surveys that are used to find water in a roof:

• Nuclear gauges - which count neutrons

• Capacitance meters - which measure resistance

• Infrared - which measures heat.

Both nuclear gauges and capacitance meters are used to take spot readings on a 5’ X 5’, 10' X 10' or 20' X 20' grid on the roof. These measurements are used to extrapolate where the water is from the readings obtained from the gauges. These surveys are very labor-intensive and therefore expensive. They are good for types of roofs that do not gain or lose much solar energy and therefore do not lend themselves to infrared.

Roof Infrared Basics

During the day, the sun radiates energy onto the roof and into the roof substrate, and then at night, the roof radiates the heat back into outer space. This is called radiational cooling. Areas of the roof that are of a higher mass (wet) retain this heat longer than that of the lower mass (dry) areas. Infrared imagers can detect this heat and "see" the warmer, higher mass areas, during the "window" of uneven heat dissipation.

 

​

 

Understanding Infrared Roof Imagery

Infrared imagery is often a grayscale picture whose scales (or shades of gray) represent the differences in temperature and emissivity of objects in the image. As a general rule, objects in the image that are lighter in color are warmer and darker objects are cooler. No object in the images is detected via visible light wavelengths (400-700 nanometers) rather, only from infrared wavelengths in the 3000-5000 nanometers or in the 3-5 micrometers (microns) range. Lights and other relatively hot objects are very evident, but as a result of their heat, and not light emissions.

When an image is taken by our infrared camera, it is often recorded on videotape and/or digitally saved to a hard drive and later converted to a digital image file with the help of a computer. The image may then be modified in a number of ways to enhance its value to the end user. The highest resolution infrared images are usually found on the digital media, while the printed pictures may be used as a convenient reference when making the building drawings or accompanying a roof report.

Areas of roof moisture contamination often manifest themselves as warmer (lighter colored) areas that may be nebulous in shape and sometimes mottled in appearance, although they are commonly found in linear or puddle-like shapes. The linear shapes many times follow low areas, drainage routes, roof edges and seams. Puddle-like round or oblong shapes often form around roof penetrations such as mechanical equipment, standpipes, vents and drains. The wet areas are lighter in color because the latent heat (from daylight sunshine) in the trapped water mass is greater than in the dry, functioning insulation or roof substrate. After sunset when the roof structure cools down, wet areas of roof insulation and other materials continue to radiate heat, allowing our sensitive infrared cameras to detect the sources of heat and record them for later analysis.

​