Infrared thermal image of building facade. Image credit: iRed. Retrofit starts with identifying where and how the building is wasting energy. Infrared thermography offers a powerful solution, making the unseen visible and enabling early intervention. Many of these issues — such as heat loss, air leakage and moisture ingress — are invisible to the naked eye. ISO 6781-1:2023 - Performance of buildings — Detection of heat, air and moisture irregularities in buildings by infrared methods  establishes the standard for using infrared thermography in building diagnostics, ensuring consistent and reliable assessments.  These three simple physical concepts — heat , air and moisture — form a powerful foundation for understanding how qualitative infrared thermography reveals hidden building defects. Heat loss Temperature variations within a building can reveal much about its thermal performance. Infrared thermography detects heat loss caused by settled cavity wall insulation, thermal bridges and other structural inefficiencies. These issues create temperature gradients, often resulting in thermal discomfort. To compensate, residents may increase heating levels, driving up energy consumption and costs. Beyond financial implications, these cold spots can lead to condensation when surface temperatures fall below the dew point. This moisture accumulation significantly increases the risk of mould growth, which can have serious health consequences. Identifying and addressing these thermal inefficiencies is key to improving indoor comfort while reducing energy waste. Air leakage Draughts are a common but often overlooked source of energy inefficiency. Infrared thermography can detect air infiltration and exfiltration points, from defects in dot and dab wall construction to gaps around doors and windows. These leaks enhance convective heat transfer, leading to unwanted heat loss and temperature fluctuations. Addressing air leaks through effective draught-proofing is one of the simplest and most cost-effective ways to enhance a building’s energy efficiency. Sealing these gaps not only prevents unnecessary heat loss but also improves overall indoor comfort, reducing reliance on heating systems and lowering energy bills. Moisture intrusion Water damage can be one of the most destructive forces in a building, yet early-stage moisture issues often go undetected until significant damage occurs. Infrared thermography is instrumental in identifying moisture ingress from sources such as breached damp-proof courses, roof leaks or plumbing failures. Unchecked moisture creates an ideal environment for mould growth, which is linked to respiratory illnesses and other health problems. By identifying moisture intrusion before visible damage appears, infrared thermography enables proactive maintenance, preserving both property value and occupant health. Things to remember It’s important to understand that these issues remain undetectable through standard visual inspections or RGB cameras. Infrared thermography provides an advanced diagnostic method , revealing surface temperature patterns that indicate underlying issues.  Problems such as moisture ingress may begin subtly and worsen over time. By identifying and addressing these issues early, building owners and contractors can improve energy efficiency, enhance thermal comfort and reduce health risks. Infrared thermography drives informed decisions about energy efficiency improvements and preventative maintenance strategies. In upcoming posts, we’ll explore these issues in the context of retrofit projects, particularly in pre- and post-retrofit assessments and long-term performance monitoring.

High-resolution infrared thermal images capture qualitative details. Image credit: iRed. Infrared thermography (IRT) is a widely used technique for assessing buildings, helping to identify issues related to heat loss, insulation and air leakage. However, not all thermal imaging methods are the same. Two distinct approaches — qualitative and quantitative thermography — serve different purposes. Understanding their differences is essential for interpreting thermal data accurately. Qualitative thermography: expert-led building diagnostics Qualitative thermography is a diagnostic tool that relies on the skill and expertise of the operator  to interpret thermal images. This approach identifies patterns, temperature differences and anomalies  that indicate potential issues . It is particularly valuable for: Detecting insulation defects  and thermal bridging Pinpointing air leakage  that contributes to energy inefficiency Identifying moisture infiltration , which can lead to mould and structural damage Assessing retrofit effectiveness  and construction quality assurance Why operator expertise matters Qualitative thermography requires an experienced operator who understands the context, physics and limitations of thermal imaging. A trained thermographer must consider: Environmental factors  such as wind, solar gain and recent weather conditions that may influence surface temperatures Building materials  and how different surfaces absorb and emit infrared radiation The time of day  and temperature differences required for an effective survey Common misinterpretations , such as reflections, which can distort thermal images With the right expertise, qualitative thermography transforms raw images into actionable insights. In inexperienced hands, however, anomalies can be easily misinterpreted — leading to incorrect conclusions. The role of quantitative thermography Quantitative thermography attempts to measure absolute temperatures and compute precise thermal properties (like U-values). It requires carefully controlled conditions and is typically used for: Laboratory testing of building materials Scientific research into thermal resistance (R-values) and heat flow Certain industrial and medical contexts where exact temperature metrics are critical What makes it quantitative? To produce trustworthy temperature or heat-flow measurements, quantitative surveys need: Calibrated cameras  with verified accuracy Steady-state conditions  indoors and outdoors Accurate knowledge of material properties , including emissivity Additional instruments  like heat flux plates to measure actual heat flow In everyday, real-world building surveys — particularly external ones — these conditions are rarely met. Temperature fluctuations, wind and solar gain introduce large uncertainties, making truly quantitative results difficult to validate. The key takeaway When it comes to practical building surveys, qualitative thermography  is typically the go-to method. In skilled hands, it quickly locates problem areas and provides visual evidence that can guide repairs or retrofits. While quantitative thermography  has its place in controlled environments (e.g., labs and specialised research settings), attempting to apply it casually to everyday building surveys often leads to misleading data. By recognising these differences, building professionals can select the right approach for their needs — whether it’s an expert-led qualitative scan to pinpoint problem areas or a carefully controlled quantitative study for precise heat-flow measurements. Further reading Husein, H. A. (2022). Thermal Imaging for Improving Energy Conservation Behaviors: An Infrared Thermography Survey for Residential Buildings. International Transaction Journal of Engineering, Management, & Applied Sciences & Technologies, 13(9), 13A9L, 1-17. Retrieved from  https://tuengr.com/V13/13A9L.pdf   Ferreira, A. T. V., Ferreira, P., & Santos, M. M. (2024). A qualitative analysis using thermography for characterization of the built environment. Eng, 5(1), 477-494.  https://doi.org/10.3390/eng5010026   Al-Habaibeh A., ALLINSON, D, Redgate, JS and Medjdoub, B , 2006. The application of infrared thermography for energy conservation in buildings. In: Proceedings of The Joint International Conference on Construction Culture, Innovation and Management, Dubai.