Abstract: The installation for determining the thermal resistance of a wall comprises a first measuring unit applicable to the inner side, respectively the warm side of the building element, the unit comprising a measuring plate made of heat conducting material having a given thermal resistance of which one face is intended to be applied to the building element and of which the other face is in thermal contact with an adjustable plane heating body. The measuring plate provides by means of thermocouples arranged on either face a reference signal corresponding to the heat flow through the measuring plate to an electronic control and calculating unit. Furthermore a second measuring unit arranged on the outer side or cold side of the building element comprises at least one contact plate made of heat conductor material covering the measured area and connected to the control and circulation unit by at least another thermocouple.