Abstract: An assembly for installing building systems engineering units includes a housing, which comprises a control device for carrying out an electronic function, and a base module which is designed for fastening the housing for a pre-determined installation situation. The housing and the base module are designed for fixed but removable connection so that the housing can be connected to a base module adapted to the respective installation situation in dependence on the installation situation. The modular sub-division of an installation unit into a base module and a housing, which comprises the control device for carrying out a defined function, can significantly reduce the diversity of variants.