Caravan roofs made of fiberglass (GFK) are not glued on the right and left sides over the entire length of the roof for a width of 20 cm. Full-surface adhesion would lead to cracking noises, tensions, and tearing of furniture connections to the roof due to the material's tendency to expand. The expansion joint allows the material to expand freely. This can manifest as several individual bulges or as a continuous elongated bulge. This has no impact on quality and durability and does not constitute a defect.