Ubakus-Style U-Value Calculator
Estimate the thermal transmittance (U-value) of a wall or roof assembly by entering up to four material layers. This is a simplified educational calculator inspired by the Ubakus workflow.
Layers (inside → outside)
Default surface resistances used: Rsi = 0.13 and Rse = 0.04 m²K/W.
What Is an “Ubakus Rechner”?
The phrase ubakus rechner usually refers to an online building-physics calculator used to evaluate wall, roof, and floor assemblies. In practice, people use this kind of tool to estimate key values such as thermal resistance, U-value, and potential heat loss through a component.
While professional planning still requires complete calculations and local code checks, a Ubakus-style calculator is excellent for early-stage decision-making. It helps homeowners, builders, and energy consultants compare material options quickly.
How This Calculator Works
1) Thermal Resistance Per Layer
Each layer contributes thermal resistance based on:
R = d / λ
- d = thickness in meters
- λ = thermal conductivity in W/m·K
2) Total Resistance and U-Value
We add up all layer resistances and include interior/exterior surface resistance. The U-value is then:
U = 1 / Rtotal
Lower U-values generally mean better insulation performance and lower heating/cooling demand.
3) Heat Flow Estimate
The calculator also estimates instantaneous heat loss:
Q = U × A × ΔT
- A = area in m²
- ΔT = indoor-outdoor temperature difference
How to Use It for Better Envelope Design
- Compare insulation thickness options before purchasing material.
- Test different lambda values (for example, mineral wool vs. wood fiber).
- Identify weak assemblies with high U-values and prioritize upgrades.
- Use output as a screening step before a full hygrothermal check.
Best Practices and Limitations
A simplified ubakus rechner is very useful, but it does not replace full building-physics design. Real projects should also account for:
- Thermal bridges at studs, beams, and junctions
- Air tightness and convective heat losses
- Moisture transport, condensation risk, and drying potential
- Climate zone assumptions and code-specific requirements
For permit-level work, always confirm results with a qualified professional and local regulations.
Quick Interpretation Guide
- U > 0.40 W/m²K: Typically weak insulation, likely improvement needed.
- 0.20–0.40 W/m²K: Moderate performance, often acceptable in retrofits.
- < 0.20 W/m²K: Strong thermal performance, common in high-efficiency envelopes.
Use the calculator repeatedly with small changes in thickness and material properties to find a cost-performance sweet spot for your assembly.