Ground floor – insulation above slab (floating floor)

Ground floor – insulation above concrete slab

Thermal insulation is positioned above a ground floor slab when the building’s heating is used intermittently – like in many homes, where it is often switched on in the morning and again in the evening.

When insulation is installed above a concrete slab, the screed or flooring board that receives the final floor finish is not attached to the building structure, and is therefore considered to be ‘floating’. Compared to insulation installed below the concrete slab, there is little or no thermal mass and therefore the rooms warm up and cool down more quickly.

What Polyfoam XPS products are suitable above a concrete floor slab?

In domestic properties, insulation installed above the concrete slab is the most common ground floor construction type. Due to the relatively low loads imposed on these floors, Polyfoam Floorboard Standard is the perfect choice.
For larger domestic-type buildings, as well as office and commercial developments, Polyfoam Floorboard Extra offers the same thermal efficiency, and a higher compressive strength to bear the load of a denser screed and a more intensive building use.

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. Product benefits include:

  • High compressive strength and protects the damp proof membrane from damage.
  • Highly resistant to water absorption.
  • Robust and can tolerate traffic from following trades.
  • British Board of Agrément certificate.
  • Environmental Product Declaration.
  • BES 6001: Responsible Sourcing of Construction Products.

Why should I consider extruded polystyrene (XPS) for a floating floor?

The standard method of construction is to install the concrete slab and damp proof membrane (DPM) on the prepared ground. The layer of thermal insulation follows, then a polythene separating layer/vapour control layer (VCL) and floating floor covering.
As long as it offers sufficient compressive strength, almost any type of rigid insulation can therefore be considered, because it is surrounded by two membrane layers, protecting it from ground water, and moisture and alkalis in the concrete slabs and screeds.

Installation errors are surprisingly common, however. The most commonly encountered error is installing only a single membrane layer, placing the DPM above the insulation and exposing the boards to potentially harmful conditions that degrade their performance.

Extruded polystyrene (XPS) insulation is unique in its tolerance of damp or wet environments – so if an error is made, its thermal performance will not suffer and the floor will continue to achieve the intended U-value. XPS insulation provides a flat, strong and dimensionally stable base for the floating screed or flooring board, reducing the likelihood of defects in the floor covering or finish.

Recommended Polyfoam XPS products for above floor slab applications are: