Airtightness Failure After Drywall in a Phius CORE Project
A 40-unit, five-story Phius CORE project in Denver (climate zone 5B) is nearing completion. The third-party rater's blower-door test reports 1.1 ACH50, well above the 0.6 ACH50 limit. Drywall is finished and painted. The general contractor proposes a 'seal-and-retest' campaign: spray foam around outlets and top plates, seal penetrations, and retest in two weeks. The owner has a certificate-of-occupancy inspection in three weeks and a Phius certification deadline in six weeks. The design team's model assumed 0.6 ACH50. The rater notes that the test was done before elevator-shaft fire caulking and before ERV commissioning; several dryer vents were open, and one unit's patio door was not yet weatherstripped. The contractor wants to test a 10% sample of units and average the results to save time.
1. Diagnose the most likely leakage paths and evaluate the contractor's seal-and-retest plan.
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The 1.1 ACH50 result is a system failure, not a cosmetic one. Likely paths include top plates and rim joists, mechanical and electrical penetrations, recessed lights, elevator-shaft and stairwell interfaces, party-wall and floor-slab junctions, dryer vents, and incomplete weatherstripping at patio doors. The rater's own notes identify incomplete work: elevator-shaft fire caulking, ERV commissioning, open dryer vents, and a missing door seal. That means the first test is not a valid final test, but it is still useful as a diagnostic. The contractor's plan to spray foam around outlets and top plates may help, but it is not targeted. It should begin with a smoke or infrared survey to locate leaks, then seal the identified paths, then retest. Averaging a 10% sample is not acceptable as a substitute for the required whole-building or unit-by-unit protocol unless the certification program explicitly allows sampling; averaging can hide a failing unit and does not prove the building meets the limit. The team should also confirm test conditions and that temporary sealing is documented and removed.
2. Recommend a remediation and verification plan that protects the certification deadline.
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Treat the next two weeks as a diagnostic and repair window, not a single retest. First, complete the missing scope: fire-caulk the elevator shaft, weatherstrip the patio door, close and seal dryer vents, and commission the ERVs. Then run a diagnostic blower-door test with smoke or infrared scanning to map leaks by floor and unit. Prioritize air-barrier continuity at floor slabs, party walls, penetrations, and window openings. Use durable sealants and backer materials, not temporary tape. After repairs, retest the whole building or follow the program's unit-by-unit protocol. If the result is close to 0.6 ACH50, do a second targeted scan and repair before the final test. Keep the certifier informed and document every repair with photos and a leak log. The six-week certification deadline is tight but workable if the team stops guessing and uses the first test as data. A failed final test would be far more costly than a one-week diagnostic delay.
3. What are the Phius QA and certification implications if the final test remains above 0.6 ACH50?
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Airtightness is a mandatory requirement, not a tradeable metric. If the final verified test remains above 0.6 ACH50, the project cannot be certified as Phius CORE on that basis, and the design team cannot substitute a modeled infiltration rate for the measured result. The certifier should require a root-cause report, a repair plan, and a new test. If the building is occupied or drywall is closed, remediation may require opening selected cavities, which is disruptive and expensive. The project team should also revisit the WUFI Passive model: if the as-built airtightness is worse than assumed, heating demand, peak load, and moisture risk change. The owner should be told that the certificate-of-occupancy schedule and the Phius deadline are at risk. The QA file should include all test reports, the leak log, repair photos, and the final passing test. Do not accept a sample average or a test with temporary sealing as proof of compliance.