Calculate the U-value of your wall, roof or basement ceiling layer by layer, check the German legal limit and subsidy eligibility, and estimate your home's heat load.
Guidance, not a certificate
The U-value applies to homogeneous layers under EN ISO 6946; rafters, studs and thermal bridges are not included and there is no condensation check. The heat load is an estimate. Sizing a heat pump requires a room-by-room heat load calculation to EN 12831-1, and the subsidy requires confirmation by an accredited energy efficiency expert.
Enter the layers from inside to outside
Layers (inside → outside)
↑ inside
↓ outside
0.22 W/(m²K)
U = 1 / R = 1 / 4.553 m²K/W
Total thickness
41.0 cm
Inner surface temperature
19.1 °C
Heat flux
6.8 W/m²
≤ 0.24 W/(m²K) · met
Missing insulation (λ 0.035): none
GModG Annex 7 no. 1a/1b
≤ 0.20 W/(m²K) · not met
Missing insulation (λ 0.035): + 2 cm
BEG EM TMA no. 1.1 "external wall"
Temperature profile at 20.0 °C inside and -11.1 °C outside (design outdoor temperature of the chosen location).
| Layer | d [cm] | λ | R [m²K/W] | Share |
|---|---|---|---|---|
| Internal surface resistance (Rsi) | 0.13 | 3 % | ||
| 1. Lime/lime-cement plaster | 1.50 | 1.00 | 0.015 | 0 % |
| 2. Solid brick (ρ 1600, old building) | 24 | 0.68 | 0.353 | 8 % |
| 3. Mineral wool λ 0.035 | 14 | 0.035 | 4.000 | 88 % |
| 4. Lime/lime-cement plaster | 1.50 | 1.00 | 0.015 | 0 % |
| External surface resistance (Rse) | 0.04 | 1 % | ||
| Total R | 41.0 | 4.553 | 100 % |
The maximum applies when you renew, replace or install the element for the first time and more than 10% of the area of that element group is affected (§ 36 GModG). If the insulation thickness is technically limited, the thickest possible layer with λ 0.035 is sufficient (λ 0.045 for blown-in or renewable insulation).
A single measure is only eligible for the subsidy if the U-value meets the technical minimum requirement. New funding guidelines apply since 17 Aug 2026 — the values shown come from the BEG EM technical annex of 21 Dec 2023 and must be checked before applying.
A rough figure for the whole house
11.5 kW
Building (space heating): 10.9 kW · Hot water allowance: 0.6 kW
Specific heat load
78 W/m²
Design outdoor temperature
-11.1 °C
Temperature difference
31.1 K
For sizing a heat pump this figure is only a starting point. A room-by-room heat load calculation to EN 12831-1 is the basis for sizing, hydronic balancing and the subsidy application.
Assumptions: typical values per construction period at 20 °C inside and −12 °C outside, scaled to your temperature difference. Envelope method with a thermal bridge allowance of 0.10 W/(m²K), factor 0.6 for elements against ground/basement, air volume = living area × 2.5 m. Hot water: 0.2 kW per person (rule of thumb).
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