Ground floor – insulation below slab

Ground floor – insulation below slab

For the hard-wearing, non-decorative floors of industrial buildings and some commercial buildings, the concrete slab often acts as the floor finish as well as load bearing element. Thermal insulation can therefore only be installed below the slab.

In other ground floor constructions, featuring floor coverings and floor finishes, there is a choice whether to install the insulation layer above the slab or below the slab. The building’s heating regime usually dictates the choice; insulation placed below a floor slab typically suits a system of continuous, low-level heating, where the thermal mass of the concrete will not be repeatedly warmed and allowed to cool.

Many insulation products, when installed below the ground floor slab, must be laid above the damp proof membrane (DPM) to protect them from ground water. A separating layer is then required over the insulation layer to protect it from the concrete slab.

Extruded polystyrene (XPS) is unique among widely-available thermal insulation materials for its tolerance of damp or wet environments. That means it can be laid directly on prepared ground, with the DPM laid over it also acting as the separating layer between insulation and concrete – a saving of both time and membrane material.

The superior load-bearing performance of XPS lends itself to the demands of storage/racking and vehicle movements in warehousing and other industrial environments. It can also be used below raft slabs in residential and other low-rise buildings, offering the opportunity to enclose the entire fabric within the thermal envelope, reduce linear thermal bridging at junctions between construction elements, and achieve a greater level of building performance, comfort and energy efficiency.

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 below floor slab applications are: