Infrared Inspections of Flat Roofs
Sponsored by: Testo Inc.
Infrared Inspections of Flat Roofs
Tip written by: Infraspection Institute
Infrared inspections can be especially helpful in formulating a roof maintenance program. As with other types of infrared inspections, several interdependent factors can affect a thermographer’s success. Before beginning an inspection, there are several things that one must consider to help ensure accurate data collection.
Roof Construction: Applicable roof construction is as follows: Built up or single-ply membrane installed over, and in continuous contact with, a layer of insulation or an insulating deck. Roof may be either smooth, granule, or gravel-surfaced. If gravel surfaced, stones should be pea sized or smaller.
Roofs covered with concrete pavers or river washed ballast (walnut sized rock) are not candidates for an accurate infrared inspection.
Roofs with thick insulation systems may be difficult to image when moisture is present only at the bottom of the insulation layer.
Equipment: For highly reflective and smooth-surfaced roofs, use a short wave (3-5 micron) imager to overcome reflections caused by nighttime sky. For gravel or granule surfaced roofs, one may use either a long wave or short wave camera with good results.
Time of Day: In general, infrared inspections are best performed at night after a sunny day; however, there are several environmental factors which will influence the ability to collect accurate data. Minimum weather requirements are as follows:
Recent rain sufficient to cause wetting of roof components
Dry roof surface at sunrise. No ice, snow or standing water
Mostly sunny day
Daytime highs above 40°F
Daytime winds of less than 15 mph at the rooftop
Nightime winds of less than 15 mph at the rooftop during IR inspection
No rain on day of infrared inspection
Roofing Materials: Some materials are more difficult to inspect than others. Roofs having lightweight concrete or gypsum can be more difficult to inspect because they can retain significant quantities of moisture either left over from construction or due to building usage.
For roofs having an insulation layer, the absorbency of roof insulation can also affect one’s ability to detect moisture as well as the intensity and type of thermal patterns observed.
Water Ingress: Not all water that enters a roofing system will enter the insulation system. Infrared inspections rely on moisture being absorbed by roofing system components causing a change in thermal capacity or thermal conductivity. Should water bypass the roof insulation, no unusual thermal patterns will be observed.
Moisture Content: The amount of moisture within the roofing system will have a direct impact on the images observed. The clear, well-defined IR images found in text books are not always found in the field.
Additionally, roofs which are completely saturated will not exhibit clear thermal patterns but will often exhibit a mottled thermal pattern.
Moisture Verification: To ensure accuracy all infrared data must be verified through invasive testing and the results correlated with infrared data. Remember, an infrared imager is not a moisture meter.
Experience: Because thermography is an art as well as a science, an experienced operator may be able to shed some expertise on difficult roofs. This is a situation where working with a mentor can be especially helpful or you may wish to work with an experienced infrared consultant who specializes in roof inspections.
Proper conduct and documentation of infrared inspections of flat roofs is detailed in the Standard for Infrared Inspections of Insulated Roofs. Copies of this comprehensive document are available in PDF format through the Infraspection Online Store.
