Supporting · Floor insulation
Solid floor insulation explained
What solid floor insulation means and how it differs from suspended timber floors.
In short
Solid floor means a concrete slab sitting directly on the ground, with no void underneath. Common in post-1950s UK homes. To insulate, you lay rigid insulation boards on top of the slab, then new screed or floating floor. Cost: £2,500 to £6,000 for a whole floor.1
Solid vs suspended floors
- Solid floor: Concrete slab on the ground. No void. To tell: tap the floor (sounds solid), lift carpet (you see concrete or screed).
- Suspended floor: Timber floorboards over joists, with a void underneath. To tell: tap the floor (sounds hollow), look for air bricks in external walls.
How to insulate a solid floor
Two methods:
- Overlay: Lay insulation boards on top of existing floor, then new screed. Raises floor level by 120mm to 180mm.
- Dig-out: Lift existing floor, dig down, lay insulation, pour new screed. Keeps floor level but more expensive.
Materials
- EPS boards (100mm to 150mm): Cheap (£20 to £30 per m²).
- PIR boards (80mm to 120mm): Thinner, more expensive (£35 to £50 per m²).
When is it worth it?
Only during major renovation. Payback is 25 to 40 years, so prioritize loft and walls first.1
Related reading
Sources
- Energy Saving Trust (2026). Floor Insulation. energysavingtrust.org.uk/advice/floor-insulation/. Accessed May 2026.