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2021 IECC Climate Zone 3A: Vented Attic, 2x6 Wall, Basement with Interior Insulation

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2021 IECC Climate Zone 3A: Vented Attic, 2x6 Wall, Basement with Interior Insulation
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Notes

IECC CZ 3A: Vented Attic, 2x6 Wall, Basement with Interior Insulation

  • 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 rigid insulation where the basement concrete slab intersects the exterior concrete basement wall has two lines of continuous sealant. The first seals the concrete slab edge to the interior surface of the insulation. The second seals the back surface of the rigid insulation to the concrete foundation wall. The two seals provide air control layer continuity between the concrete slab and the concrete wall to control radon and other soil gases.
  • The removable unfaced batt insulation installed in the band joist should be cut to fill the entire perimeter cavity for the full width of the foundation wall. This avoids significant thermal bridging through the foundation wall and sill plate. It should be removable to allow for termite inspections.

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