It is not easy to solve the entire envelope of a building, both façade and roof, with a continuous mantle of slopes varying from 0% to 100%. Tightness in the façade plane, where gravity acts in our favour, has been entrusted to geometry and drainage. However, this solution is not possible on the roof. The changes of slope in a topography of rounded ridges generates practically zero slope planes, which can only be resolved with absolutely waterproof materials.
