U-value Calculator
The insulation thickness divided by the thermal conductivity gives the resistance of the panel; adding the two surface resistances and taking the reciprocal gives U. The method is EN ISO 6946, and the surface temperature and mould check EN ISO 13788.
The thermal resistance of the steel sheets is neglected; for 0.5 mm steel R = 0.00001 m²K/W against a total resistance between 2 and 9. EN 14509 accepts that omission.
The surface is 8.6 K above the dew point. The mould limit is met as well.
The critical surface humidity is taken as 80%; the standard gives this where there is no national value. For corrosion, 60% is used. The internal surface resistance in the surface calculation is 0.25 m²K/W, not the 0.13 used for U: this allows for corners, furniture and suspended ceilings. The result belongs to the single condition entered, not to the worst month of the year.
Fastener correction The number and type of screws belong to the project
Because screws pass from sheet to sheet, they carry heat around the insulation and raise U. Annex F of EN ISO 6946 gives a correction for this, but its inputs belong to the project rather than to the panel: the number of screws comes from the structural calculation and the type from the corrosion category. Where the correction stays below 3% of U, the standard does not require it to be applied.
The U-value for the selected application; the small grey figure is the R value at the same thickness. The thicknesses listed are the ones produced, and an empty cell means that core is not produced at that thickness.
| CORE | λ | 20 | 30 | 40 | 42 | 50 | 60 | 70 | 80 | 100 | 120 | 130 | 150 | 160 | 180 | 200 |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| PIR | 0.022 | 0.930.91 | 0.651.36 | 0.501.82 | 0.481.91 | 0.412.27 | 0.352.73 | 0.303.18 | 0.263.64 | 0.214.55 | 0.185.45 | · | 0.146.82 | 0.137.27 | 0.128.18 | 0.119.09 |
| PU | 0.022 | 0.930.91 | 0.651.36 | 0.501.82 | 0.481.91 | 0.412.27 | 0.352.73 | 0.303.18 | 0.263.64 | 0.214.55 | 0.185.45 | · | 0.146.82 | 0.137.27 | 0.128.18 | 0.119.09 |
| Rock wool | 0.045 | · | · | 0.940.89 | · | 0.781.11 | 0.671.33 | 0.581.56 | 0.511.78 | 0.422.22 | 0.352.67 | 0.332.89 | 0.293.33 | · | 0.244.00 | 0.224.44 |
| Hybrid | 0.045 | · | · | 0.940.89 | · | 0.781.11 | 0.671.33 | 0.581.56 | 0.511.78 | 0.422.22 | 0.352.67 | 0.332.89 | 0.293.33 | · | 0.244.00 | 0.224.44 |
| EPS | 0.038 | · | 1.040.79 | 0.821.05 | · | 0.671.32 | 0.571.58 | 0.501.84 | 0.442.11 | 0.362.63 | 0.303.16 | · | 0.243.95 | · | 0.204.74 | 0.185.26 |
U = 1 / (Rsi + d/λ + Rse). The surface resistances come from Table 9 of EN ISO 6946 according to the direction of heat flow: 0.10 upwards, 0.13 horizontal, 0.17 downwards, and 0.04 externally in all three. The single U-value printed for a product in the catalogue is calculated for horizontal flow; the standard uses the horizontal values for a declaration independent of direction.
The value given is the value of the panel itself. Thermal bridges from joints, the structure and the installation are not included; the effect of the fasteners is calculated separately in an optional step.
The λ values come from one place, by core material. The result is directly proportional to λ: if λ changes, every figure on the page changes.
