This document specifies a test method for the in situ measurement of the thermal performance of buildings, both newly built and existing. This document specifies the data to be collected during and after the test. NOTE The analysis of the data and the reporting format for the analysis are referred to in prEN 17887-2:2022 Thermal performance of buildings In situ testing of completed buildings Part 2: Steady-state data analysis for aggregate heat loss test. This document is applicable to domestic scale detached buildings and attached domestic scale buildings, such as semi-detached houses, terraced houses and apartments.