Floor calculator
Floors
Dedicated page for ground floors, slabs, and intermediate floors with typical build-ups and guidance.
Common floor build-ups and practical decision points.
Ground floor slab
Requires insulation beneath the slab or below the screed, depending on the design.
Intermediate floor
Often driven by thermal, acoustic, and fire requirements together.
Lightweight floor
A modern retrofit option with leveling and insulating layers.
Foundation slab
Needs careful edge detailing to limit thermal bridges and heat loss.
1. Choose the floor type
Pick a ground floor, slab, intermediate floor, or retrofit build-up.
2. Build the layer stack
Use the main calculator to add layers, set thickness, and edit lambda values.
3. Check the U-value
Compare the result against the target and export the report if needed.
A floor is more than a U-value number. The build-up has to fit the structure, the moisture conditions, and the way the space will be used.
In practice, floor insulation is about balancing heat loss, structural build-up, moisture behaviour, and the need for a comfortable finish. Ground floors are usually designed differently from intermediate floors, because the performance targets and constraints are not the same.
Ground floors
For slabs on grade, insulation is often placed below the slab, below the screed, or as part of a perimeter and slab-edge strategy. The edge zone matters as much as the centre area.
Intermediate floors
These floors are often driven by acoustic comfort, fire resistance, and vibration control as much as by thermal performance. The thermal layer still matters, but it is only one part of the whole design.
Retrofit floors
When floors are upgraded in existing buildings, the available height is limited. That makes material choice, load capacity, and careful detailing especially important.
A well-designed floor build-up should feel straightforward when you look at it as a sequence of layers: support, insulation, moisture protection, service layers, and the finished surface.
The floor usually fails at the edge, at the junction, or when the layer sequence is not realistic.
Perimeter and slab edge
The slab edge is often the coldest part of the assembly. Perimeter insulation and careful junction design help keep the heat flow under control.
Load and thickness limits
Floor assemblies must carry loads and still leave enough room for finishes, levelling, services, and insulation. A good thermal solution must also be buildable.
Moisture and ground conditions
For floors on ground, the layer sequence should account for moisture, capillary rise, and the need to protect sensitive materials from damp conditions.
The best floor build-up is usually the one that solves the thermal target without making the rest of the construction awkward, fragile, or hard to build on site.
A floor can look simple on paper and still perform badly if the details are rushed.
1. Forgetting the edge zone
A floor that is well insulated in the centre but weak at the perimeter will not behave like the calculator result suggests.
2. Building up thickness without planning the finish
Extra insulation can create issues with thresholds, doors, stairs, and service routing if the finished floor level is not planned in advance.
3. Mixing thermal and acoustic layers without checking compatibility
Intermediate floors often need both thermal and acoustic performance. The layers should work together instead of fighting each other.
4. Not verifying the whole assembly
Even a small change in material or thickness can alter the final U-value, so the full structure should always be rechecked after edits.
A quick final check before you freeze the floor build-up.
- The insulation is continuous where the floor needs it most.
- The slab edge or perimeter zone has been addressed.
- Moisture, load, and finish height have been considered together.
- The target U-value was checked in the calculator.
- Lambda values were checked against the technical data sheets.
Common floor questions
Can I calculate ground floors?
Yes. Add layers from the soil side to the finished surface and check the overall U-value.
Can I calculate intermediate floors?
Yes. Model the real layer build-up and compare insulation options.
Are floors calculated the same way as walls?
Yes. It uses the same thermal model, but with floor-specific layers and assumptions.