Worked Example · Ground Floor (floating)
Ground Floor (Floating) U-Value Worked Example
An insulated ground-bearing concrete slab, assessed with the ISO 13370 simplified method and checked against the Approved Document L (2021) limit of 0.11 W/m²K for ground floors.
Build-up layers
| # | Layer | Thickness (mm) | λ (W/m·K) | R (m²K/W) |
|---|---|---|---|---|
| — | External surface resistance (Rse) | — | — | 1.459 |
| 1 | Screed | 65 | 0.410 | 0.159 |
| 2 | PIR insulation | 200 | 0.022 | 9.091 |
| 3 | Concrete slab | 150 | 2.000 | 0.075 |
| — | Internal surface resistance (Rsi) | — | — | 0.170 |
Perimeter/area ratio: P/A = 40/100 = 0.40 m⁻¹
Calculated U-value
0.091 W/m²K
Total resistance R = 10.953 m²K/W
ADL 2021 limit
0.11 W/m²K
England — Approved Document L (2021), new dwellings
PASS
The calculated U-value of 0.091 W/m²K is at or below the 0.11 W/m²K limit — compliant with ADL 2021.
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