Caravan and motorhome roofs with GRP are not glued on the right and left on a width of 20 cm over the entire roof length. A full-surface bonding would - due to the material's tendency to expand - lead to cracking noises, tensions and tearing of furniture joints to the roof. The expansion joint gives the material room to expand unhindered. This can take the form of several individual elevations as well as one continuous elongated elevation. This has no effect on quality and durability and does not constitute a defect.