An installation for detection and measurement of stratification around drains/outlets (1) on building roofs for drainage of liquids, in particular environmentally induced stratification (6, 7) such as water and/or ice, comprising at least one sensor and at least one control and measuring system (23). The piezoelectric transducers (2) transmit acoustic waves into the formed layers (6, 7) via a suitable contact medium (5) and a suitable sealing compound (4). Each of the piezoelectric transducers (2) with sealing compound (4) may alternatively be encapsulated into a protection case (3), which again is mounted/installed underneath the contact medium (5). By measuring reflection coefficients and time delays between the transmitted acoustic waves and their reflections from interfaces and surfaces of the stratifications, layer information such as detection, identification and thicknesses may be achieved. The installation may preferably also comprise at least one weight system to complement said layer information, give additional information such as amount of snow (8, 34) and detect undesirable intrusion of foreign matters (10). A preferred embodiment is to integrate a heating system (26) with the said installation, where engagements and disengagements of said system (26) depend on the measurement results from the transducers (2) and the weight systems (9, 35).