Sauna & Cabin Roof Insulation Calculator (Dew Point Check)
Calculate insulation requirements for heated cabins and saunas. Features a simplified dew point warning system to prevent internal roof condensation.
About
Small, detached heated structures like saunas or garden offices face a unique challenge: massive temperature differentials. When the interior is 80°C and the exterior is −10°C, the risk of condensation forming inside the roof layers is extremely high. This leads to mold, wood rot, and insulation failure.
This tool calculates the total thermal resistance (R-value) of your roof assembly and performs a check on the critical interface between insulation and the roof deck. It suggests whether a vapor barrier is strictly required and if the insulation thickness is sufficient to keep the dew point outside of the structural layers.
Formulas
The risk of condensation is estimated by calculating the temperature Tx at the interface between the insulation and the outer sheathing:
If Tx is lower than the Dew Point Temperature (Tdp), condensation will occur unless a perfect vapor barrier is present.
Reference Data
| Material | R-Value per inch | Vapor Permeability | Typical Use |
|---|---|---|---|
| Mineral Wool | 3.7 | High (Permeable) | Cavity Fill |
| PIR Board (Foil) | 6.5 | Zero (Barrier) | Under Rafters |
| EPS Foam | 3.8 | Low | General |
| Cellulose | 3.5 | High | Loose Fill |