Floor insulation is a layer of thermally resistant material installed in or under a floor to prevent heat loss to the ground or unheated spaces below. It is a key component of an energy-efficient building envelope.
Why Floor Insulation Matters
An uninsulated ground floor can account for up to 15 percent of a building’s total heat loss. Insulating the floor reduces energy consumption, lowers heating bills, and improves comfort by eliminating cold surfaces underfoot.
Types of Floor Insulation
- Rigid foam boards — polystyrene (EPS or XPS) or polyisocyanurate (PIR) panels placed below or above the floor slab
- Mineral wool — glass or stone wool batts fitted between timber joists in suspended floors
- Spray foam — applied to the underside of suspended timber floors for complete coverage
- Loose-fill insulation — granular materials blown into the space beneath raised floors
Installation Methods
- Below the slab — insulation boards are laid on a sand-blinded base before pouring the concrete slab, common in new construction
- Above the slab — boards are placed on top of an existing slab, with a screed or floating floor laid over them
- Between joists — batts or spray foam are fitted in the cavities of suspended timber floors, often from the underside via a crawl space
Application
Floor insulation is used in residential homes, commercial buildings, and renovations. It is especially important for:
- Ground-floor rooms over unheated crawl spaces or cellars
- New builds that must meet modern energy performance standards
- Retrofit projects to improve an older building’s thermal envelope
- Reducing condensation risk and moisture problems at floor level
Proper installation includes a vapour barrier where needed and attention to thermal bridging at wall-floor junctions.
Related Terms
- Thermal bridging
- Crawl space ventilation
- U-value
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