Field Testing and Diagnostic Evaluation of Air Barrier Systems
Field testing answers two different questions: how leaky is the system, and where is it leaking? Quantitative tests - whole-building fan pressurization per ASTM E779 or E1827, zone or compartment testing, and field air leakage of installed fenestration per ASTM E783 - produce numbers comparable to a threshold. Qualitative diagnostics per ASTM E1186, including smoke tracers, infrared thermography, theatrical fog, and tracer gas, locate the paths.
Good practice requires a stable baseline, recorded indoor-outdoor temperature and wind, and awareness that gusty or stack-driven conditions bias results. Run at a defined reference pressure, commonly 50 Pa for whole buildings, and normalize so results compare: air changes per hour at 50 Pa, cfm per ft² of envelope, or cfm per ft² of floor area. Report the basis; a bare cfm50 figure is not a result.
Trap: testing before the boundary is complete and closed, or leaving interior doors open so the measured zone is not the intended zone. Another trap: counting duct leakage, combustion appliance zone depressurization, or open exterior doors as envelope leakage. Multi-zone testing requires adjacent zones to be controlled, otherwise the reading reflects the path of least resistance.
Worked example: a 12,000 ft³ building measured at 3,000 cfm50 gives ACH50 = 3,000 × 60 ÷ 12,000 = 15. If the same building has 6,000 ft² of envelope, that is 0.5 cfm/ft² at 50 Pa - a very different framing of the same measurement, and the one a specification may actually limit.