Underfloor Insulation

What is Underfloor Insulation?

Underfloor insulation is any thermal insulation installed within or beneath a ground floor to slow the movement of heat out of the building. It's worth distinguishing it from underfloor heating insulation, which is designed specifically to sit beneath an underfloor heating system and reflect heat upward into the room rather than letting it escape into the floor structure.

The two products often work together because good floor insulation makes your underfloor heating system far more efficient.

The right approach depends entirely on your floor type. The two most common ground floors in UK homes are suspended timber floors and solid (concrete) floors, and each is insulated in a different way.

Suspended Timber Floors

Suspended timber floors are floorboards fixed to joists above a ventilated void. They’re more commonly found in UK homes built before the 2000s. The gap beneath them makes them a notable source of draughts and heat loss, but it also makes them relatively straightforward to insulate.

Insulation is fitted between the joists, typically using mineral wool slabs (which also add acoustic benefit) or rigid PIR boards cut to fit. Where access to the void is possible, this can often be tackled as a retrofit or DIY project.

Solid floors

Solid floors refers to a  concrete slab or screed laid on the ground. Concrete floor insulation is achieved by laying a layer of rigid insulation board over the slab, followed by a new floor build-up on top.  Because these boards carry the floor load, compressive strength and moisture resistance matter.

PIR boards are the popular high-performance choice, while XPS suits damp or below-ground conditions and EPS offers a cost-effective option for larger areas. This work is usually part of a renovation, extension or new build rather than a quick retrofit.

Benefits of Underfloor Insulation

• Reduces heat loss through the floor and lowers energy bills
• Eliminates draughts from suspended timber floors for a warmer, more comfortable home
• Improves the efficiency of underfloor heating systems
• Adds acoustic benefit when using mineral wool between joists
• Helps meet UK Building Regulations U-value targets for floors
• Suitable for both retrofit and new build projects

Why Choose Insulation UK?

• Competitive pricing on all floor insulation, with no minimum order value.
• Fast UK-Wide Delivery with free shipping available on qualifying orders.
• Expert Support from a team with over 50 years of industry experience to help you choose the right insulation for your floor.
• Bespoke Cutting Service to size boards for awkward joist spacings and last-minute adjustments.