What Is a Vapor-Open Wall Assembly?
Vapor-open assemblies (the drying — the both directions; the >10 perms) let the moisture escape (the built-in — the construction's; the incidental — the leaks') — the assemblies without the interior vapor retarder (the mild climates' — the drying). The design: the materials' (the perms' — the outward-increasing), the climate's (the drying's — the potential), and the verification (the WUFI's — the modeled). The wall's — the breathing.
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How open assemblies work
The drying (the outward — the vapor's; the inward — the summer's; the both), the materials (the mineral wool — the open; the wood fiber — the hygroscopic; the membranes' — the variable), and the sequence (the perms' — the outward-increasing; the trapping's — the avoided).
When to use
The mild (the marine — the drying's; the Zone 4C's), the retrofits (the existing — the drying's needed; the safe), the mass (the masonry's — the reservoir's; the drying), and the new (the high-performance — the modeled).
Vs. the retarder
The cold (the retarder's — the required; the Zone 6+'), the mixed (the smart's — the variable; the forgiving), the air (the barrier's — the still required; the vapor's — the distinct), and the WUFI (the verification — the climate's; the assembly's). The open is the drying — the retarder is the blocking.
The bottom line
Use vapor-open assemblies (>10 perms, outward-increasing) in mild/marine climates and drying-needed retrofits — always maintain the air barrier; verify with WUFI.
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