Concrete floor insulation: how to insulate a solid slab floor

How do you insulate a concrete floor?

Solid concrete floors sit directly on the ground with no void. To insulate, you either:

• Overlay method: Lay insulation boards on top of the existing floor, then new screed or floating floor on top. This raises the floor level by 120mm to 180mm, which can cause problems with door heights and steps.
• Dig-out method: Lift the existing floor, dig down, lay insulation boards, pour new screed. Keeps the floor level the same but much more disruptive and expensive.

Materials and cost

Typical materials:

• EPS boards (100mm to 150mm): Cheap (£20 to £30 per m²), good compressive strength.
• PIR boards: Thinner (80mm to 120mm for the same U-value), more expensive (£35 to £50 per m²).

Cost: £2,500 to £6,000 for a whole ground floor (overlay method). Dig-out method: £4,000 to £10,000.

When is it worth it?

Concrete floor insulation is only worth it if:

• You're doing major renovation (new kitchen, bathroom, complete refurb).
• You've already insulated loft and walls (do those first, faster payback).
• Your floor is noticeably cold (you can feel the cold through your feet).

Payback is 25 to 40 years, so this is low priority unless you're renovating anyway.¹

Related reading

• Is floor insulation worth it?
• Suspended floor insulation guide
• Solid floor insulation explained