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Weather-Specific Region 4C Building Assembly:

Unvented Attic, 2x6 Wall with Exterior Insulation, Frost-Protected Shallow Foundation
IECC CZ 4C Map
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2021 IECC Climate Zone 4C: Unvented Attic, 2x6 Wall with Exterior Insulation, Frost-Protected Shallow Foundation

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2021 IECC Climate Zone 4C: Unvented Attic, 2x6 Wall with Exterior Insulation, Frost-Protected Shallow Foundation

Notes

IECC Climate Zone 4C: Unvented Attic, 2x6 Wall with Exterior Insulation, Frost-Protected Shallow Foundation

  • Provisions from Section R806.5 of the 2021 IRC should be followed to allow for the installation of an unvented attic, including considerations for vapor control, minimum thickness of air-impermeable insulation (by Climate Zone), and ignition barriers.
  • The water-resistive barrier (WRB) is shown installed between the continuous insulation and the wall sheathing. Alternatively, the WRB can be on the exterior of the continuous insulation. In either case, all flashing details must ensure water is directed to the outside of the WRB.
  • The R-5 rigid insulation on the exterior of the wall framing allows the wall to be constructed without an interior vapor barrier according to the provisions in Section R702.7 of the 2021 International Residential Code. To maximize drying potential in the wall assembly, the interior side of this wall assembly should not have a Class I vapor retarder.
  • Rim joist insulation should align with R-value requirements for above-grade exterior walls.
  • Exterior cladding fastening requirements should follow guidelines from cladding manufacturer or Section R703.15 of the 2021 IRC.
  • Backfill placement should prevent damage to exterior continuous insulation.
  • Exterior insulation should be protected above grade.
  • Provisions in Section R403.3 of the 2021 IRC should be followed to determine the R-value, depth, and placement of insulation to satisfy frost-protected shallow foundation requirements.
  • Horizontal sections of insulation should be installed in accordance with Table R403.3(1) of the 2021 IRC.
  • Unvented attics in locations with a ground snow load greater than 50 lbs/ft2 (293 kg/m2) require venting over the insulation layer. This can be achieved by creating a vented “over-roof” (not shown in this assembly drawing). The thermal resistance of deep snow can be high enough to allow the lower level of snow in contact with the roof to melt and cause ice damming unless the roof is vented.

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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.