How much insulation for ground floor?

Ground floors often have some resistance from the slab and perimeter details, but the target U-value still drives the insulation thickness.

Best for

Worked example

How much insulation is needed to reach 0.20 W/m²K?

Ground floor calculations should include the resistance already provided by the slab and any underfloor layers.

Example build-up

Target U-value 0.20 W/m²K, existing floor resistance 1.10 m2K/W, insulation lambda 0.035 W/mK.

Result

Required insulation thickness is approximately 11.6 cm.

Floor notes

Ground contact changes the effective thermal path compared with a suspended floor.

Edges and junctions can matter a lot on ground-contact floors.

Underfloor insulation has to fit the overall floor depth available in the project.

Open the calculator for a custom floor build-up.

Read the floor-specific thickness guide.

Compare with the general floor target-U page.