<p>The thermal insulation layer (1) has recyclable insulating boards arranged side by side, where the thermal insulation layer is arranged between a building-ground (6) and a base plate (4) and is formed by the insulating boards. The insulating boards are provided along plate sides that are attached corresponding to each other, and the interlocking devices include the plate sides. The interlocking devices are formed as a groove-clip-dovetail connection and include grooves and clips on the plate sides. The insulating board is formed by heat insulating material i.e. light-weight concrete.</p>
