Planned exterior rigid insulation meets unexpected poly sheets
Hi all. I’m starting an addition/renovation on my 1920’s home in Ohio (Climate Zone 5). First bump – unexpected poly abutting the drywall in some of the walls. I’d previously encountered cellulose when coring the walls to install bathroom vents. Operating under the assumption that the insulation would be consistent (the house was renovated in the 90’s and again, in part, in the 00’s), I planned on removing the exterior siding, air sealing and installing a 1.5″ layer of polyiso board on the exterior of the house, including the new framing (2×4 walls; FWIW the wall assembly is attached). I removed the trim on the windows this past weekend and discovered that a large portion of the house appears to be batt insulation with poly sheeting abutting the drywall. I’ll pause to acknowledge what happens when you assume and what happens to best laid plans (Dana had even led me to sourcing reclaimed polyiso nearby). So…now what. Moving forward with the polyiso board would result in large sections of the walls having no pathway for drying, which feels like a pretty terrible idea. It seems like one option is to shift to 1.25″ or 2″ of Rockwool Comfortboard since that would allow drying to the exterior. Unfortunately, the Comfortboard is much higher cost than reclaimed polyiso. Another alternative would be to let sleeping dogs lie, not mess with exterior insulation and flip to 2×6 walls on the addition with either cellulose or open cell spray foam. I’d then turn my energy to air sealing as best I could on the addition and existing house. Any other ideas or glaringly obvious things I’m missing? Thanks.
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