The butyl tape serves to ensure watertightness of joints subjected to temperature expansion up to 105oC. The section of the tape is U-shaped.
The butyl tape compensates for small movements between the parts, while keeping water out. These properties make it suitable for sealing, for example, between windows on the facade, fittings, exits for communications and the overlaps of the roof panels.
The most important role is played by the roof panels where they overlap. Freezes in winter form water "basins" and thus increase the water level, and this leads to the transfer of water over the corrugation of the roof panel. In some cases, due to the very small gaps between the overlapping sheets, we also have hygroscopic return as the water climbs back up the slope thanks to its surface tension.