Understructure is made of specially hardened expanded polystyrene with its own name KLINARYT. In the upper part, called the head, a BG1 class expansion tape is glued and grooves for glue-sealant paths are marked. The head is milled with fasteners and closely fitted to a specific threshold. This is crucial for proper sealing.

A very important element is the hard PVC hitching strip integrated with the entire lower part understructure . It enables a permanent connection to the ground with steel anchors. The base is manufactured in basic dimensions with a height of Understructure mm (in 10 mm increments).