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2021 IECC Climate Zone 3A: Spray-foamed Roof, 2x6 Wall, and Floor on Pier Foundation

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2021 IECC Climate Zone 3A: Spray-foamed Roof, 2x6 Wall, and Floor on Pier Foundation
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Notes

IECC CZ 3A: Spray-foamed Roof, 2x6 Wall, and Floor on Pier Foundation

  • The attic insulation in this unvented attic is located on the underside of the roof sheathing. To prevent moisture issues at the roof deck, one or more of the following vapor-control approaches can be used:
    • Use air-impermeable insulation such as spray polyurethane foam (open cell or closed cell).
    • Install airtight vapor diffusion ports, allowing air-permeable insulation such as cellulose or fiberglass to be used. 
    • Install minimum R-5 air-impermeable insulation against the roof deck, allowing air-permeable insulation such as cellulose or fiberglass to be used to make up the rest of the total R-value requirement of R-49. The air-impermeable insulation can be spray polyurethane foam or rigid foam board (with joints sealed), installed against the underside of the roof decking or on the exterior side of the roof decking.
    • Install a vapor-permeable roof underlayment and vapor-permeable roofing (such as tile), allowing air-permeable insulation such as cellulose or fiberglass to be used.
    • Install dehumidification in the attic space.
  • Unvented attics are more resistant to wind uplift under hurricane conditions.
  • If a raised-heel roof truss is used to allow R-38 attic insulation over the full width of the exterior wall, then R-38 can be used throughout the attic rather than R-49. See Section R402.2.1 of the 2021 IECC for additional information.
  • A class III vapor retarder is used on the interior surface of the walls and ceiling instead of a vapor barrier. This allows drying to the interior. Avoid vinyl wallpaper and oil-based paint or coatings in Climate Zone 3. These wall coverings are vapor impermeable and increase the risk of condensation within the wall.
  • The protection board under the floor prevents animals from damaging the assembly.

Disclaimer

This content is a work created with funding provided by the United States Department of Energy under Contract no DE-AC05-076RL01830 for the operation of Pacific Northwest National Laboratory. The information and guidance provided by Pacific Northwest National Laboratory (PNNL) in the content are intended solely for educational purposes only and do not constitute formal training or certification. It is provided with the explicit understanding that neither the United States Government nor the United States Department of Energy, nor the Contractor, nor any or their employees, nor any jurisdiction or organization that has cooperated in the development of these materials, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness or any information, apparatus, product, software, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof, or Battelle Memorial Institute. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof. Viewers assumes full responsibility for all actions that they may take from information provided in this content including ensuring the safety, code compliance, and proper functionality of any products they choose to install. Installation and use of such products should be performed in accordance with local regulations and manufacturer instructions.