Wall calculator
External walls
Dedicated page for layered wall assemblies, with build-up guidance, typical materials, and U-value logic.
Common wall build-ups and practical decision points for external walls.
Masonry + insulation
The most common build-up for cavity walls and retrofit insulation.
Timber frame wall
Needs careful attention to thermal bridges, vapour control, and insulation thickness.
ETICS system
Lightweight insulation layer, adhesive, mesh, and render as a complete facade system.
Cavity wall
A durable option with a facing leaf and an insulated cavity.
1. Choose the wall type
Pick masonry, timber frame, cavity wall, or ETICS as the starting point.
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.
How wall insulation should be designed and installed for reliable thermal performance.
Good wall insulation is not only about choosing a low lambda material. The complete wall build-up must be continuous, airtight where needed, and free of weak points at junctions, openings, and structural connections.
1. Keep insulation continuous
Insulation should cover the wall surface without gaps, compression, or repeated interruptions. Continuous layers perform better than patchy local additions.
2. Reduce thermal bridges
Pay attention to corners, floor slabs, window reveals, lintels, and balcony connections. These zones can weaken the effective U-value if they are not insulated properly.
3. Match the vapour strategy
The wall should allow moisture to be controlled in a way that suits the assembly. Vapour control, windtightness, and drying direction must be considered together.
4. Verify the result
After setting the layers, use the calculator to check the final U-value, adjust thickness where needed, and compare materials if you want better performance.
Small details often decide whether the wall performs as designed.
Openings and reveals
Window and door reveals should be insulated carefully so the edge zones do not become weak thermal bridges.
Junctions with slabs and roofs
The wall insulation should connect cleanly to floor slabs and roof layers. Gaps at junctions can undermine the calculated U-value.
Moisture and drying
Choose a layer sequence that allows the wall to dry in the intended direction and avoids trapping moisture in sensitive layers.
In practice, the best wall build-up is the one that combines continuous insulation, controlled vapour movement, and careful detailing at every junction.
The most frequent reasons why a wall performs worse than expected.
1. Ignoring junctions
A wall can have a good calculated U-value and still lose performance if the edges, corners, and interfaces are not insulated correctly.
2. Choosing thickness without checking the system
Thicker insulation is not always better if it causes build-up conflicts, moisture issues, or installation problems around openings and fixings.
3. Mixing incompatible layers
The sequence of materials should make sense as one system. A good wall needs compatible structural, vapour control, insulation, and finishing layers.
4. Skipping final verification
Always recheck the full wall assembly after changes. Small adjustments in lambda or thickness can noticeably change the final result.
A quick check before you freeze the wall build-up.
- Continuous insulation covers the full area.
- Openings, reveals, and junctions are detailed.
- Vapour and wind control match the assembly.
- The target U-value has been verified in the calculator.
- Material lambda values were checked against technical data.
Common wall questions
Which materials are best for walls?
It depends on the target, but low lambda and the right insulation thickness usually improve U-value the most.
Can I calculate single-layer walls?
Yes. Add one structural layer and check the result without extra insulation.
Does this page calculate only walls?
No. The main calculator also handles roofs, floors, and other layered assemblies.