Insulated ground floor slab, SOPRATHERM GA4000
Concrete slab, 100 mm PIR board over it, and a 65 mm screed — insulation above the structure, under the finish.
Layers, outside to inside
| Layer | Thickness | W/(m·K) | R |
|---|---|---|---|
| Reinforced concrete (generic) | 150 mm | λ 2.3 | 0.07 |
| SOPRATHERM GA4000 | 100 mm | λD 0.022 | 4.55 |
| Screed (generic) | 65 mm | λ 1.4 | 0.05 |
Where this fits
Insulating above the slab puts the screed inside the thermal envelope, which warms up quickly and suits underfloor heating; insulating below it instead gives the room the slab's thermal mass, which evens out temperature swings but takes far longer to respond. Either is defensible — decide by how the room is heated and used, not by U-value alone. Perimeter upstand insulation at the slab edge matters more than the last 20 mm of thickness here.
What the calculation assumes
Series calculation only. Ground floor heat loss properly depends on the floor's shape and exposed perimeter (ISO 13370), which this does not model, so treat the figure as indicative of the build-up rather than of the floor. Surface resistances are the EN ISO 6946 defaults for this element. This is an indicative figure for comparing constructions, not a compliance calculation.
Sources
- SOPRATHERM GA4000 — declared data · checked 2026-08-25
Change it, or use it
Open it in the calculator to swap a layer, change a thickness or solve for a target U-value — the result keeps its own URL, so a build-up you have altered is still something you can send to someone. Or take this one straight into the editor, where it arrives as a named wall type you can assign to the walls you have drawn: the thickness follows and the U-value comes with it. Nothing is assigned until you say so.