The thermal behaviour of a building is often underestimated or neglected during its construction and operation stages. In recent years, the heat flux meter (HFM) method has been commonly used to determine the U-value, a key parameter for assessing the thermal quality of the building envelope in steady-state conditions. However, this non-invasive test takes at least 72 h to execute, the accuracy is\ud 14–28%, and it is not reliable for non-homogeneous building elements. An alternative technique is based on infrared thermography (IRT). Although it is generally used for qualitative analysis, quantitative internal IRT methods may also be adopted for in-situ measurement of the U-value. This research presents\ud a method for determining in-situ U-values using quantitative internal IRT with a deviation of 1–2% for single-leaf walls and 3–4% for multi-leaf walls. It takes 2–3 h and can be used to provide information about the building envelope for the future refurbishment of existing buildings or to check the thermal behaviour of new building façades according to their design parameters.Peer ReviewedPostprint (author's final draft

Exceptional pandemic lockdown measures enabled singular experiments such as analysing the energy consumption of vacant buildings. This paper assesses the impact of the COVID-19 lockdown on the energy use of academic buildings. For this purpose, weather-adjusted energy use was compared before and during the lockdown, including different levels of lockdown restrictions. Results obtained for the 83 academic buildings of Universitat Politècnica de Catalunya - Barcelona Tech (UPC) reveal that the avoided energy consumption amounted to over 4.3 GWh during the post-pandemic year. However, the results indicate that academic buildings were still using approximately 46.9% of their typical energy consumption during strict lockdown. This revelation emphasizes the high environmental burden of buildings, regardless of whether they are occupied.