Establish systems thinking: heat, air, and moisture flows are coupled, so changing one often changes the others. This sets up the logic behind control layers and unintended consequences.
Builds on: P3 (loads) and P4 (failure mechanisms) · Leads to: P6-P11 · Cross-series: A5 House Size & Design
P/A bridge: Compact design reduces not only cost but also transition count, mechanical load, and failure risk.
| Tighten air barrier | Ventilation/pressure change; verify mechanical ventilation sized to new tightness |
| Add insulation | Colder sheathing; verify drying potential and condensation risk at new temperature profile |
| Add exhaust fans | Depressurization; verify makeup air path and combustion safety |
| Seal crawlspace/attic | Moisture/pollutant paths shift; verify new pressure boundary is complete |
In Northern Colorado: dry outdoor air does not eliminate condensation risk when air leakage reaches cold surfaces; smoke events make uncontrolled leakage an IAQ failure, not just an energy penalty.
Coupled-flow failure patterns: "warm air finds cold surface," "pressure does the damage," "drying path got blocked," "small leak + time."
1. Exfiltration into a cold roof zone
2. Basement/garage odor and humidity
3. "We sealed it up and now it's wet"