The cost of land continues to rise and space on sites is increasingly constrained, especially in densely populated areas. It’s little surprise, therefore, that designs for new buildings, and extensions in particular, are as likely to consider going down into the ground as they are to go ‘up’ or ‘out’.

Any usable floor space that sits below ground level is classed as a basement. The entire space can be underground or, due to varying levels or a sloping site, part of the space may be at ground level and part may be below ground.

The effect of the ground, particularly its thermal capacity, changes the heat loss characteristics of walls and floors below ground level and influences how insulation is specified. Choosing whether to position insulation on the inside or outside of the basement structure also depends on the material’s capability to resist the static pressure of the soil, and its tolerance or wet environments.

Enclosing the basement structure within the thermal envelope helps to reduce linear thermal bridging at junctions between construction elements, and achieves a greater level of building performance, comfort and energy efficiency. The superior load-bearing performance of extruded polystyrene (XPS) means it is capable of resisting the significant loads placed on insulation below basement floor slabs and external to basement walls.

Polyfoam XPS Ltd is a leading manufacturer of closed cell, extruded polystyrene insulation. The Polyfoam range is lightweight, strong, moisture resistant and easy to cut and shape, providing thermal performance and strength for the lifetime of the building. Recommended Polyfoam XPS products for basement applications are: