Occupied Clinic Moisture and Commissioning Failure
Summit Builders is renovating a 4,000-square-foot occupied medical clinic in Omaha in three phases. Phase 1 replaces exterior windows and adds a new 25-ton rooftop unit; phase 2 builds two exam rooms; phase 3 replaces ceiling tiles and flooring. The clinic stays open, with immune-compromised patients in adjacent suites. During a 15°F cold snap, staff report condensation on the new double-pane windows, a musty odor in exam room 2, and ceiling stains near a new supply duct. A hygrometer reads 68% RH indoors; the new RTU is set to 72°F and 20% outdoor air. The contractor has not commissioned the RTU; the duct joints above the ceiling are taped but not sealed. The window installer used low-expansion foam at the rough opening but no sill pan. The owner wants to open phase 2 in two weeks.
1. Diagnose the likely moisture and IAQ problems and rank them by urgency.
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The immediate priority is the musty odor in the occupied clinic, because it suggests microbial growth or a ventilation defect near immune-compromised patients. The 68% indoor RH during a cold snap is high; the new RTU is providing only 20% outdoor air and may not be dehumidifying, and the duct joints above the ceiling are not sealed, so humid air can condense on cold surfaces. The ceiling stains near the supply duct point to condensation or a duct leak, not necessarily a roof leak. The window condensation is likely a combination of high indoor humidity and a missing sill pan or air leakage at the rough opening; low-expansion foam alone does not flash the sill. The sequence should be: isolate and dry the affected area, sample or inspect for mold, correct the duct sealing and RTU operation, verify outdoor-air and dehumidification, and repair the window flashing. Do not open phase 2 until the source is controlled and the clinic has been monitored for several days.
2. What commissioning, infection-control, and owner-communication steps should Summit take before phase 2?
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Summit should commission the RTU before occupancy, including airflow, refrigerant charge, economizer, condensate drainage, and controls calibration. It should verify that the building pressure is slightly positive and that outdoor air meets the design; 20% may be a design value, but it must be confirmed. Duct joints should be sealed and tested, and ceiling tiles should not be replaced until the plenum is clean and dry. Infection control should include negative pressure in the work zone, HEPA filtration, daily cleaning, and coordination with clinic staff; the musty room should be closed until cleared. The owner should receive a written corrective-action plan with dates, a mold assessment if visible growth is found, and a schedule impact notice. The two-week phase 2 opening is at risk; the contractor should not promise turnover until commissioning and moisture readings are acceptable. Document all communications because the owner may later claim delay damages.