Long-term degradation of U-values: A dataset of experimental evidence and energy performance consequences

This dataset contains experimental U-value measurements collected over a three-year period (2022-2025) for various building envelope components, including front and back external walls, internal partitions, and roofs. The data reflects real-world degradation in thermal performance due to ageing and material changes. Each component is documented through raw CSV data, detailing the experimental setup, environmental conditions, and measurement duration. The dataset is intended to support research in building energy performance, retrofit evaluation, and the development of predictive models for thermal ageing in construction materials.