In most buildings with a cellar, garage or rooms below ground, earth-retaining walls are those that dissipate most heat due to the low temperatures of the ground that comes into contact with the wall. Moreover, below-ground rooms are being used increasingly to make them more livable. Thermal insulation is extremely important and extruded polystyrene is especially recommended for this type of application not only because of the excellent thermal insulation values, but also because of the great compressive strength. In this application, the pressure exerted by the ground on the thermal insulation requires the use of insulation with high compressive strength.

Laying:walls need to be duly protected and waterproofed. The X-FOAM^® HBT 500 insulation layer can then be laid making sure to fit them together closely. The panels are applied dry and by points starting from the bottom. The insulating layer is to be protected by a waterproof sheath. The last step is to fill the wall's extrados making sure to apply a filtering fabric on the insulating layer and a layer of gravel between the fabric and the ground to allow filtering so that the ground does not ruin the insulation panels.