Existing brick over 1″ foil-faced EPS in zone 5A: Plans for air-sealing & re-insulating from the interior
Thank you for the opportunity to benefit from the GBA community’s experience. My project is a 1950s ranch with 2×4 walls sheathed with horizontal 1×6 and 15# felt. An addition was added in 1985 with 2×4 walls sheathed with 1″ EPS foam with steel let-in bracing. No wood sheathing. The foam has a mechanically-perforated aluminum foil on a thin cardboard facer. The same EPS foam was applied to the entire original structure over the felt and 1×6 at the time of the addition, then T-111 wood siding over all. EPS seams have overlapping facer-flanges but were not taped. The T-111 was stripped in 2007, the entire structure wrapped in thoroughly-taped Tyvek and bricked.
Submitted for your criticism and comments is the proposed air-sealing and insulating plan intended to be implemented entirely from the interior:
Original 1950 Structure Walls: Roll on a silica-based fluid-applied membrane air barrier (Sto Gold Coat, >10 perms for two 10-mil coats) onto the 1×6 to air seal the many tiny cracks and splits, then embed vapor-open fabric (Sto Fabric) over the larger gaps between the 1x6s. Ring each stud bay with a 3/8″ fillet of low voc silyl-terminated polyether (BASF NP150) to air-seal the 1×6 to the studs. Install foaming shells around electrical boxes (BoxShells). Insulate with unfaced (to enable full 6-sided cavity contact and allow use of drywall adhesive) R-15 fiberglass batts. Glue and screw drywall (Denarco gaskets or Dow drywall gasket in a can). Prime with vapor retarder primer (0.6 perm, Sherwin Williams). Inject latex foam into BoxShells.
1985 Addition Walls: No Sto Gold Coat. Air seal by ringing each stud bay with ProClima Contega HF sealant (adheres well to EPS and has low modulus to tolerate the expansion coefficient difference between wood and EPS). Seal electrical, insulate and drywall per above.
1985 Addition Wall with Shower: Two stud bays on a NW wall will receive a solid surface (Swanstone) shower cladding over paperless gypsum tile backer board (Denshield) and will not be able to dry inward. These bays will sealed with Contega HF, and then receive 3-1/2″ of tightly-fitted cut-and-cobble XPS foam to mitigate inward vapor drive and to increase the shower wall temperature for comfort. The XPS will be air-sealed by taping to the face of the studs using ProClima Vana tape to which drywall adhesive will adhere.
1.) I did not see any difference in the total perms calculation for all the materials in the 1×6 walls with and without Sto Gold coat. It appears to be dominated by the lower perm materials. Am I overlooking a downside to the Sto Gold Coat?
2.) Is this air sealing and insulating plan acceptable in my climate zone for these three example walls? I prefer to stay with a DIY approach using R-15 fiberglass batts for their workability and ability to easily cut down larger sizes to fit old, irregular stud bays that are sometimes up to 17″ wide.
3.) Does anyone have any experience with the Dow drywall gasket in a can versus the Denarco gaskets for air-tight drywall?
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