building envelope, hot box, quantitative thermography technique, thermal bridging
Heat losses through thermal bridges substantially influence the thermal standard of a building envelope. At design stage, these losses, expressed in terms of the linear thermal transmittance or Ψ-value, can be estimated from tabulated values for standard building details or from numerical modelling. However, these approaches are not applicable for existing building envelopes with unknown internal structure. In these cases, in-situ measurement of the Ψ-value is necessary. In this study, a methodology to measure the actual thermal bridging performance is developed. The methodology is based on a quantitative infrared thermography technique (ITT), which is easy-to-use and implementable on any existing thermal bridge. To ensure high accuracy, temperature-dependent surface heat transfer coefficients are evaluated using the surface temperatures recorded by the infrared camera. The methodology has been validated in a steady state in a hot box device with excellent agreement.