Spotlight on Roofs - It's That Season Again!

by Ron Lucier
ITC Regional Thermography Course Manager

Spring time is roof inspection season in the Northern climates. As I have been getting many calls about this topic, I felt the need to address some of the most important questions thermal imager users face during a roof inspection.
Who? You. There are certain skills that the average thermal imager user needs to acquire prior to becoming successful at roof inspections while using their thermal imagers. Roof knowledge is essential. The biggest skill you need to require is PATIENCE. Thermal imager users are accustomed to instant results.  In most cases, if you look at a bearing or piece of electrical switchgear and either is in operation, analytical data is probably present. Unfortunately that is not the case with a roof. The Physics of radiation and heat transfer teach us that there are only certain times of the day and night that are appropriate for an inspection and produce quality thermal imager photos. More on this topic later.
What? The typical inspection by a thermal imager is on “low-slope” commercial roofs. Please do not refer to these as flat roofs – your credibility will be in question. A roof must be pitched (sloped) so that water can drain off. If it was truly flat it would not technically be a roof but a very shallow swimming pool when it rained.
Why? A roof seems like a very simple concept, but in fact roofs are integrated systems that provide structural integrity, prevent water intrusion and provide building insulation. When a roof fails the most common effect is the introduction of water into the roof system, primarily into the insulation. This can result in serious damage to the roof – extra weight, loss of R-value for the insulation and potential damage to the materials and equipment inside. An inspection with a thermal imager that produces crystal clear images can locate the wet areas, and only those areas may need to be repaired. Repairing 5000 square feet of roof is much less expensive than replacing 100,000 square feet.
How? There is an ASTM procedure available to help you become familiar with roof inspections (ASTM C1153 available from http://www.astm.org). This is the standard guideline that has been in use for over 15 years. It provides a good – but not perfect – approach to general roof inspections. The two methods that are covered are the walk over method and the fly over method. It does not address my favorite technique, the walk under method (done during the morning so I can sleep at night…).
When? That is the big question and is the focus of our two day roofing course. The general requirements happen only a few times a year in most locations. Weather is usually the biggest factor in affecting the quality of the survey with a thermal imager.  If the weather is bad enough, you may not even be able to conduct the survey with your thermal imager.
Safety! People using thermal imagers have fallen from roofs and lost their lives. The subject of roof safety could be addressed in an article this size all by itself. In general I prefer two helpers in addition to the thermal imager user. One helper marks the locations of the thermal indications, the other watches out for those who are conducting the inspection with thermal imager. Preceding an inspection, a walk on the roof in daylight is strongly recommended as well as a thermal imaging inspection of the structure underneath the roof. Roofs do have a history of collapse.
Special Issue - ASTM C1153 was written when most of the thermal imagers in operation were short-wave. Most of the thermal imagers sold today are long-wave. These long-wave thermal imagers work fine on most roofs but certain membranes, particularly black EPDM, and under certain conditions (clear sky) the roof looks like a mirror! The emissivity of black EPDM is high in the long-wave thermal imager (about 0.92).
We are accustomed to think that this should help us but if the roof is cold – below 40 ºF and there is a clear sky (really cold), the roof is very efficient at reflecting the cold sky. The thermal imager photo to the right shows reflections and the warm areas associated with a large leak.  The good news is that you can still use your thermal imager regardless.   However, you should be aware of the potential for significant reflection.
Conclusion – The use of thermal imagers for roof inspections has an extensive history of success (I have been inspecting roofs with thermal imagers since 1984). There is a wealth of information presented in our roof course so if you wish to learn more about your thermal imager, or come and teach us a few things you may want to register for one.

For more information on thermal imagers for the roofing industry, please visit http://www.flirthermography.com/industries/industry/1043.

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