This article demonstrates that foam plastic insulation (polyiso board and spray polyurethane foam) can be used in code-approvable wall assemblies that work in cold, warm, marine and humid climates. Architects will be able to create alternatives to vapor permeable wall assemblies that address three main concerns: NFPA 285 flame spread tests, mitigating moisture retention within walls, and delivering higher insulating performance with greater levels of comfort.

As buildings use less and less energy to heat and cool by owner demand, HVAC systems offer increasingly less assistance in drying out walls. The HVAC systems are no longer designed to take on additional loads caused by moisture in walls that needs to be removed. However, energy bills may increase beyond expectations to address wall moisture issues with no discernable benefit to the occupants if moisture in walls is not addressed.


Learning Objectives

  • Examine NFPA 285 approved wall assemblies that use foam plastic insulation in cavity walls and rain screens.
  • Understand how insulation manufacturers can assist architects in attempting to secure approval from code officials without first performing time consuming NFPA 285 tests on the wall assembly proposed for their project.
  • Describe the importance of using continuous insulation in wall assemblies.
  • Find alternative wall designs that might provide better insulating performance and better prevention of moisture penetration/accumulation than vapor permeable wall designs.