Is there value in flash and batt with today’s IECC requirements?
I’m asking that question as a homeowner, not builder or sales rep. Also, specific to new construction homes. I am building a new 4000sf, two-zoned heat pump all electric house in Maryland (zone 4A). I am using a spec home builder, and my options don’t include exterior insulation. The one option they have been pushing me toward is flash and batt on the above grade walls only, and maybe the garage ceiling under living spaces. The typical walls are vinyl siding, house wrap, either plywood or OSB (haven’t asked to confirm), 2×6, R19 batt, and drywall.
So, I am new to this site and FHB, but I have crammed many houses reading and listening and came away with a few observations. Exterior insulation is best, but I don’t have that option here. Due to the studs, the increase in whole wall R-value I get with 1 inch of closed cell spray isn’t much. 1 inch is fine for my climate zone with regard to condensation though.
My jurisdiction is pretty strict about blower door testing to verify the required 3ACH50 requirement. The upgrade cost to flash and batt will add about $50 to my monthly mortgage. If the base house cost already includes air sealing enough to get below 3ACH50, will I really get any benefit from the optional flash and batt? Would the answer be different if I were to fill the cavities with open cell instead?
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