The aims formulated nationwide and internationally to the climate protection can be achieved by combining of the energy-efficient construction and rehabilitation of the existing buildings. Knowledge about the construction and the material identity values of the warmth-transferring outside components is a condition for the energetic balance of buildings. The essential information to this can frequently be no more taken from the construction documents particularly for older buildings since they are no longer traceable or incomplete. At the example by univalve and bivalve out-wall construction it is shown that the thermophysical qualities can be determined with the help of in-situ measuring procedures and FE-simulation calculations without destruction. © Ernst & Sohn Verlag für Architektur und technische Wissenschaften GmbH & Co. KG.