Introduce bulk water, air, vapor, and thermal control as the core taxonomy. Continuity and verification are central to performance - a layer that stops at a transition isn't a layer.
Builds on: P5 (system interactions) · Leads to: P7-P10 (specific control layers and assemblies) · Cross-series: A6 Materials & Labor
P/A bridge: Which control-layer details are most likely to fail because the labor sequence is unrealistic?
Core Concepts
Each control layer has a distinct function. Can label each layer in common assemblies.
Continuity beats material selection. Can prioritize connections at transitions and penetrations.
Verification differs by control type. Can plan testing/inspection appropriate to each layer.
What Good Looks Like
Clear definition of each layer: water control, air control, vapor control, thermal control.
Continuity of each layer around the whole building (not just in the "field" of the wall).
Alignment so layers support each other instead of creating traps.
Buildability: details people can execute consistently.
Control-Layer Mapping Template
For any assembly or transition, fill in each layer. If you can't name it, that's the risk.
Water control layer
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Air control layer
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Vapor control layer
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Thermal control layer
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Most likely continuity break
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Where Things Go Wrong
1. Window opening with great WRB but leaky air barrier
Bulk water stays out, but air leakage drives moisture into the opening; comfort complaints and hidden condensation
Layer miss: air control discontinuity; Check: blower door with smoke at window perimeter
2. Slab edge: "warm floor" isn't just comfort
Missing thermal control at the slab edge creates cold surfaces, condensation risk, and discomfort - often read as "drafty"
Layer miss: thermal discontinuity; Check: thermal scan slab perimeter in heating season