In the last part of our three-part series, we will discuss insulation materials and summarize what we have learned about destructive elements that can cause deterioration of materials and failure of building assemblies. There are four different physical mechanisms that can cause moisture to affect surface temperature. We will address the fourth of them in this tip.

4. Moisture detection through increased conductivity

Absorbent insulation materials which have taken on water will have an increase in thermal conductivity (decrease in R-value). If there is a temperature difference of at least 10 degrees Celsius across the enclosure this change in thermal conductivity can often be detected.  This does require steady-state thermal conditions (unlike thermal capacitance which requires changing conditions and does not work under steady-state). The thermal conductive method of detection, therefore, works best in summer or winter on cloudy overcast days, or in the late evening/ early morning or any time of day on north-facing walls.

Summary

Thermography can play a significant role as a non-destructive and rapid screening tool to identify potential moisture related anomalies in buildings, but only if the thermodynamic conditions are right. Building thermographers who want to do moisture inspections effectively and thoroughly need to choose multiple inspection times best suited to different conditions.

Inspectors can apply a thermal camera in a limited scope for free-air detection of evaporative cooling of water-related anomalies, so long as they have the proper knowledge, have a specific procedure detailing the method and conditions necessary for doing so and a means (e.g., a moisture detector) for immediate field confirmation of any suspected anomaly. They should document in their report the limitations of the technology, particularly the suitability (or lack thereof) of the conditions at the time for the detection of non-evaporative detection of moisture, particularly in exterior walls and roofs.

IR cameras suitable for building investigations are now inexpensive, lightweight, and easy to use. There are, however, cameras available which do not even come close to meeting the requirements for the detection of moisture anomalies. The use of infrared imaging requires training and understanding of not just the camera and infrared detection principles, but more importantly knowledge of building construction, thermal performance, and sound building science principles.  The proliferation of readily available low-cost cameras used by unqualified persons unaware of the underlying thermodynamic principles, appropriate methods, and limitations however could jeopardize the legitimate value of thermography as a valuable tool for the building diagnostic industry.

Moisture may be detected by: increased conductivity in steady-state heat transfer (figure 1); increased thermal capacitance when undergoing transient heat transfer (figure 2); and through release or absorption of latent heat once undergoing a phase change. In this case (figure 3) evaporative cooling when relative humidity is low.

We hope you have enjoyed this 3-part series. Expand your infrared knowledge with one of The Snell Group’s training courses. We also offer Level 1 Thermographic Applications, Infrared for Building Inspections, and Infrared for Roofing Inspections online on-demand.