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2021 IECC Climate Zone 2B: Vented Attic, Block Wall, Slab on Grade

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2021 IECC Climate Zone 2B: Vented Attic, Block Wall, Slab on Grade
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Notes

Drawing 2B.4: IECC CZ 2B:  Vented Attic, Block Wall, Slab on Grade

  • 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.
  • The block wall is framed on the interior with wood framing to facilitate installation of electrical services. The framing cavities are insulated with cellulose, fiberglass, or mineral wool. Although it is feasible to install the minimum-required R-6 insulation in the 2x4 wall cavity, fire code may require the entire cavity to be filled, likely resulting in a higher R-value.
  • A class III vapor retarder (latex paint) 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 2. These wall coverings are vapor impermeable and increase the risk of condensation within the wall.
  • The polyethylene vapor barrier under the concrete slab extends over the top of the CMU stem wall to act as a capillary break. 
  • Portions of the CMU wall may need to be filled solid to meet structural requirements or to accommodate anchor bolts for a sill plate.
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