Determining thickness is an engineering calculation based on:
- Local Building Code Requirements: Codes mandate minimum R-values or maximum U-values (thermal transmittance) for roofs, walls, and floors based on climate zone.
- Desired R-Value: Calculate using the formula: Required R-Value = Target R-Value – R-Value of other assembly materials.
- XPS’s R-Value per Inch: Divide the required R-value by the LTTR R-value per inch of your chosen XPS product (e.g., R-20 needed / R-5 per in = 4 inches thick).
- Other Factors: Consider moisture control, dew point location (to prevent condensation inside the wall), and space constraints. For specialized projects like cold storage, a detailed heat load calculation is performed by an engineer, considering internal temperature, external climate, and acceptable energy loss.
