Flat roofs have a roof slope from 0 to maximum 7-10 degrees and thus a decisive disadvantage: precipitation will not be derived fast from the roof area. Rain water and in winter snow or ice remain longer on the roof than it is the case with pitched roofs. The outcome of this is a load impact that should not be underestimated, as well as the requirement of the waterproof sealing. That’s why flat roofs need a high diligence and high expertise, especially connections to walls or fixtures as well as longitudinal and transverse seams are often sources of leakage.