Overview
Condition Assessment
Project Management
New Construction
Infrared Testing
Infrared Themography
Background
With the advent of thermography, roofs can be scanned with a highly sophisticated infrared camera to detect and accurately map subsurface moisture, thereby determining whether a portion or all of the roof requires replacement.   Unlike other non-destructive techniques, thermal scanning assesses every square inch of roofing including vertical flashings and around and under roof obstructions and equipment.   This results in a comprehensive view of the roof's condition, with the possibility of errors virtually eliminated.
Technical Approach
Thermography or infrared scanning is based upon the ability of a specialized infrared camera to detect variations in temperature radiating from the roof surface and convert them into an electrical signal which is displayed instantaneously as a video image called a thermogram.   This picture is displayed in a color tone similar to the image received on a color television set. The difference in tones, darker colors to lighter colors, denotes variation in the roof's surface temperature of .02 o C or more and is influenced by the moisture content of the insulation.

Under clear skies during the day, the roof acts as a large thermal collector, and can approach 160 o F during the summer months.   Any insulation laden with subsurface moisture absorbs this radiation and acts as a reservoir to regenerate the heating of the membrane after the solar effect has dissipated.   The effect of wet and dry insulation on the surface temperature of the membrane is also a result of emissive cooling. This is heat loss from the roof as much as 15 o C below ambient. In cooler weather, the introduction of moisture reduces the R-value of the assembly, producing thermal bridges. These are localized warm zones which also produce lighter colored images on the thermograms.

When an abnormality on the thermogram appears, usually as a lighter colored area, it can be interpreted to be either wet or at one time wet and has lost some of its original quality of texture and strength.