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Roof Moisture and Infrared Thermography

Fly into any city or drive around one and you will notice acres and acres of low-slope roofs. These roofs are integral to commercial buildings in particular. On average, these roofs develop a serious leak within a year of installation and, typically as a result of the trapped moisture, they degrade and about ten years later they are replaced!

The costs of this situation are astronomical! Not only can there be damage to the contents of the building, but there is also the cost of the reduced roof life. If you can double the serviceable life of a roof, the economics are staggering. As they degrade, the cost to repair or replace many roofs ends up increasing dramatically.

The fact that many roofs—the ones that are well designed, installed and maintained—can last two or three times longer suggests we are paying too much for roofs over their lives. The bottom line is: keep a roof dry and it can last twenty or more years!

Thermography allows us to locate the wet insulation in a low-slope roof. In fact, it is the only technology that, when conditions are right, allows us to view the entire roof. With that information, repairs can be made to stop the leak and, more importantly, replace the damaged insulation—keeping the roof dry.

How can we find the wet insulation? Typically we are looking for differences between the wet and dry insulation related to either thermal capacitance or conductivity. There are several ways this can be accomplished—more on that next week.

An ASTM standard (C-1153, Standard Practice for Location of Wet Insulation in Roofing Systems Using Infrared Imaging) describes how to conduct a roof moisture inspection and is recommended reading for anyone doing this work.

As mentioned earlier, we’ll talk about how to conduct a roof moisture inspection safely and effectively using thermal imaging in next week’s post.

Thinking Thermally,

John Snell—The Snell Group, a Fluke Thermal Imaging Blog content partner

4 comments to Roof Moisture and Infrared Thermography

  • CK


    One thing I like to know is, when doing roof inpsection, do you inspect the roof from the roof top, or do you inspect the roof, from inside the building and using a thermal imager looking up at the roof? (assuming that there is no insulation inside the roof).

  • Fluke Thermography

    Hi CK,

    While roofs can be inspected from either side, the most common–by far–is from the roof top. There, you are seeing the thermal signature of the wet insulation as warmer. This is due to either capacitance (wet insulation holds the heat longer) or conduction (more heat transfers from the building). Inspecting the underside of the roof deck is very problematic and often impossible. If you can see the deck from below and if it is painted metal, you may be able to see the wet insulation as more conductive (either hot or cold). Thanks for your great question.


  • we have to get a new roof

  • Fluke Thermography

    Have you done a thermal roof inspection on your place already?

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