Final answer:
Typically, the polyisocyanurate insulation is installed first because of its higher R-value, followed by EPS which counters moisture. However, installation order can vary by project specifications.
Step-by-step explanation:
When constructing well-insulated buildings, the order in which different types of insulation are installed can affect performance. If both IKO Polyisocyanurate (a type of polyisocyanurate insulation) and Expanded Polystyrene (EPS) are used within the same system, typically the polyisocyanurate insulation should be installed first. This is because polyisocyanurate has a higher R-value per inch compared to EPS and is often used as the main thermal barrier due to this property.
Polyisocyanurate is excellent at reducing heat transmission through a building's envelope and performs exceptionally well in higher temperature ranges. The EPS could then follow as it provides good insulation while also being resistant to moisture, mold, and mildew, adding those properties to the insulation system. However, the actual order may vary depending on specific building requirements and codes, and it's always best to consult the project specifications or a professional before installation.