The German Institute for Construction Technology (Deutsches Institut für Bautechnik), Berlin has given its official approval to multiple layers of BASF's Styrodur® 3035 CS, Styrodur 4000 CS and Styrodur 5000 CS used under the foundation slab. As per the company, this extends the use of the green extruded polystyrene rigid foam panels (XPS) to two or three layers as load-bearing thermal insulation under the foundation slab. The multiple layers of high compressive strength Styrodur C can provide a simpler and less expensive solution in demanding construction applications with stringent thermal insulation requirements, for example passive houses.
The thickness of each sheet can be up to 120 mm, the total thickness of the insulation layer can be up to 300 mm. The three grades are approved for areas subject to prolonged or continuous pressure generated by water, e.g. ground water. The maximum immersion depth of the sheets in these applications is 3.5 meters. For multilayer use, the approved long-term pressure value is set at 100 kPa for Styrodur 3035 CS, while for Styrodur 4000 CS it is 180 kPa and for Styrodur 5000 CS it is 250 kPa. BASF was the first and is still the only company to offer exclusively XPS panels that are free of chlorofluorocarbons (CFC), halogenated chlorofluorocarbons (HCFC) or halogenated fluorocarbons (HFC).