Infrared Thermography Provides Non-Destructive Evaluation of Structures
Dilip Choudhuri, P.E.
Walter P Moore
Xing Shi, Ph.D.
Level I Thermographer
Engineers, architects and other consultants are successfully using a unique method to support the assessment and mitigation of building envelope-related failures. Infrared thermography is a state-of-the-art technique that measures infrared radiation and generates thermal images that show thermal patterns of objects under observation. With an understanding of typical temperature signatures, problem areas can be detected as they typically show up as thermal anomalies in the acquired image. In the field of forensics, infrared thermography has become a powerful, non-destructive method to identify hidden problems in existing buildings.
Infrared thermography is the use of a non-contact thermal imaging device called an infrared thermal camera to acquire and analyze thermal signatures. An infrared thermal camera works similar to the human eye, with one important difference in its application to building envelope science. The human eyes see objects in the visible light spectrum; the advantage of the infrared camera is its ability to see objects in the infrared light spectrum (see Figure 1 below). An infrared thermal camera can detect, measure, and analyze the infrared light and generate thermal images of the objects being viewed. Thermal images can reveal hidden problems within the building envelope, making the camera an extremely useful forensic tool.
Infrared thermography is a non-contact, fast, responsive and accurate technique. Its typical applications include but are not limited to:
- Detecting hidden moisture in the building envelope - roofs, walls, and floors
- Detecting air leakage through windows, doors, and other parts of the building envelope
- Detecting mold, mildew and termite damage in buildings
- Detecting lack of insulation in walls and roofs, lack of mortar pilaster in masonry walls, blister in fiber reinforced polymer (FRP) application, etc.
The modern infrared thermal camera is portable and user-friendly, allowing the consultant to assess areas of distress in an efficient manner. However, a trained consultant knowledgeable about infrared thermal science is a pre-requisite to ensure that the data is collected and interpreted correctly.
Here are a few guidelines for using this technique for building envelope consulting:
- Detecting hidden moisture within the building envelope is one of the most common applications of infrared thermography. The best time to perform an infrared thermographic evaluation is soon after sunrise or after sunset. Areas of the building that contain hidden moisture get heated or cooled slower than dry areas of the building. This difference shows up as a thermal anomaly in the infrared thermal image.
- Every building material has an emissivity (E-value) that determines its ability to radiate infrared energy. Most infrared thermal cameras measure infrared radiation and convert it to temperature by assuming that the E-value of the building material is close to 1. This is true for most building materials such as brick, wood, steel, and concrete. However, if the object under observation has a very low E-value such as aluminum, it poses particular challenges to thermographic evaluation. Under these circumstances, special calibration needs to be performed to generate an information rich thermal image.
- To identify the problematic area that often appears as a thermal anomaly in the thermal image, heat sources are needed. The most powerful and common heat source is the sun. In some situations when it is not bright and sunny, use manmade heat sources, such as a heat gun or even a hair dryer, to heat up the object locally for infrared thermal scanning. Be creative!
- In building envelope assessments, using the infrared thermal camera to obtain the thermal images is only the first step. Proper interpretation of the thermal images is the next step towards identifying the problem. Developing repair solutions require a good understanding of infrared thermal science and relevant forensic engineering expertise.
Walter P Moore performed an investigation of a hidden water leakage problem in a large-scale students housing complex. A large number of units needed to be reviewed in a very short time: more than 1000 students housing units over a three-day spring break period. Building envelope consultants from the Structural Diagnostics Services Group that specialize in the performance of existing structures discussed this challenging project with the client and developed a plan of action. Three crews were formed, each equipped with an infrared thermal camera and moisture meters to embark on the evaluation. Each room was first scanned using the infrared thermal camera to locate thermal anomalies (Figure 2 above). Moisture content meters were then used to confirm the presence of wet spots caused by possible internal water leaks of plumbing or breaches in the building envelope.
This protocol for rapid evaluation of the student housing complex was very successful. Infrared thermography enabled Walter P Moore to rapidly scan each room and identify suspicious spots with potential internal water leakage. The evaluation of 1,000 units was completed within the deadline requested by the client.
Infrared thermography is a powerful tool for engineers, architects and consultants for use in evaluating existing buildings and structures. Infrared thermography is a fast and reliable tool to assist in identifying potential problems in existing buildings. A good understanding of infrared thermal science and relevant expertise in forensics are needed to develop a comprehensive mitigation plan.
About the authors: Xing Shi, Ph.D., has an expertise in building science and is a certified Level I Thermographer. Dr. Shi can be reached at email@example.com. Dilip Choudhuri, P.E., has expertise in the area of the performance of existing structures. Mr. Choudhuri is a Principal at Walter P Moore. He can be reached at firstname.lastname@example.org. Both are part of the Structural Diagnostics Services Group of Walter P Moore.