Rigid extruded polystyrene board – 2 cm (20 mm)

The hardest insulation to replace is usually the layer buried around the house or under a finished floor. Match boards for foundations and loaded floors to their service conditions before the layers are covered. Extruded polystyrene combines thermal insulation, low water absorption and compressive strength in places where replacing a failed layer would mean extensive work.

The closed cells of XPS limit water uptake, making the material useful on foundation and basement walls. Below ground the insulation must retain its function in conditions quite different from a dry room. Low water absorption is an advantage here over products more susceptible to moisture. A suitable layer at the base of the building helps reduce heat flow between heated rooms and the ground.

Rigid boards can also shield the waterproofing from some mechanical damage. A separate waterproof layer remains necessary. The combination is particularly useful for a basement in regular use or a heated commercial space below ground. Choose the layers carefully while the foundation is exposed because inspection will be difficult after backfilling.

A suitable XPS grade carries the pressure imposed by the designed floor build-up. In a garage, store or utility room, check that the board is rated for the expected loads. Its behaviour over time matters as well as its short-term compressive strength. The right selection helps limit heat loss while allowing the floor to serve its purpose. In a workshop, for example, the design needs to account for daily traffic and the equipment that will stand on the floor.

Regular board sizes and different edge profiles help plan cuts and form a continuous layer. Rigid boards are straightforward to fit across flat areas and around their perimeter. Depending on the grade, XPS can also be used on inverted roofs and terraces, where moisture resistance and load capacity are both important. Specifying it for the actual conditions helps make practical use of these parts of the building.

At SteelProfil you can compare thicknesses and strengths for foundations or larger floor areas. Ask about stock, the grade available for the particular batch and current offers when costing your project.