This European Standard provides guidelines for improving the energy performance of historic buildings, i.e. historically, architecturally or culturally valuable buildings, and reducing associated greenhouse gas emissions while respecting their heritage significance. The use of this standard is not limited to buildings with statutory heritage protection, but applies to historic buildings of all types and ages. This European Standard presents a normative working procedure for selecting measures to improve energy performance, based on an investigation, analysis and documentation of the building and its heritage significance. The procedure assesses the impact of those measures in relation to preserving the character-defining elements of the building.