Hello "Mottenhausen". This question is not easy to answer. It depends on the roughness of the surface and ultimately also on the surface protection itself. That means: with a tile covering, a steeper slope would be necessary due to the joints than with a smooth surface protection such as sealing or synthetic resin coating. In the professional field, we assume approximately 1.5% slope for smooth surfaces and approximately 2.5% for rough surface structures if surface water is to be drained automatically. However, this must be planned in height according to the length of the garage, because with a length of 6m, assumed here purely theoretically, the height loss at the rear part of the garage would be 9cm. There is no binding requirement for garages that a general slope must be formed in the floor. The condition that no "counter slope" leading to the wall surfaces or (depending on the architecture) to the residential building may exist must definitely be observed. If a drainage channel in the garage floor has already been structurally neglected, the surface water can only be drained outwards, thus towards the garage door. A drainage channel must be provided running parallel in front of the door so that in all cases no rainwater can penetrate the building through the garage driveway. Regards: KlaRa