Two Occupied Floors and a Two-Week Flush-Out

Do the arithmetic first - it is the whole conversation.

Flush-out path: deliver 14,000 ft³ of outdoor air per ft² of floor area before occupancy.

• 60,000 ft² × 14,000 ft³/ft² = 840 million ft³.
• At a delivered 50,000 cfm of outdoor air, that is 840,000,000 ÷ 50,000 = 16,800 minutes ≈ 280 hours ≈ 11.7 days of continuous 24/7 operation, if the system actually delivers the design outdoor air rate.

Air-testing path: a shorter pre-occupancy flush of 3,500 ft³/ft², then test.

• 3,500 × 60,000 = 210 million ft³ ÷ 50,000 cfm = 4,200 minutes ≈ 70 hours ≈ 3 days, then sampling for the target contaminant limits (formaldehyde, TVOC, particulate, CO2, ozone, and the relevant others per the credit table).

So the flush-out is roughly four times the duration and, in winter, much more than four times the energy cost - bringing in 50,000 cfm of cold outdoor air requires preheat, and possibly humidification, for nearly two weeks.

Recommendation: pursue air testing, but only with the risks managed:

• Go/no-go on formaldehyde. The new casework and carpet are the failure risk. Specify low-emitting products first; air testing is not a substitute for buying better materials.
• Budget and schedule for a possible failure. A failed test means re-flush and retest - a second lab fee and a week of schedule.
• Do not run either path in winter if it can be avoided. Sequence the scrub as late as possible or into a shoulder season so the flush uses operable conditions rather than 100% preheated outdoor air.
• Both paths require the HVAC to be fully operational, which means the controls must be verified first - coordinate with the commissioning schedule or the flush is theater.

The credit is earned by a plan that is followed, not one that is written. Develop it against SMACNA's IAQ Guidelines for Occupied Buildings under Construction and organize it around the five control measures:

1. HVAC protection. Cap every duct opening; store duct on racks off the floor, not in the parking garage where it collects exhaust and moisture. If the existing HVAC serves both occupied and work floors, isolate it - new duct and any temporary air handling must be separate from the occupied system.
2. Source control. Adhesives, sealants, paints, and carpet must meet the credit's VOC content and emission requirements regardless of which flush-out path is chosen. The schedule trap is procurement: if the subcontractor buys on price before the specification requirement is enforced, the documentation cannot be recovered and both the low-emitting materials credit and the flush-out narrative are compromised. Require submittals before purchase.
3. Pathway interruption. Sealed barriers at every penetration between work and occupied space, maintained under negative pressure relative to the occupied floors, with pressure monitoring and a daily log. Demolition dust and silica from the gut is the dominant exposure here.
4. Housekeeping. Daily wet sweeping or HEPA vacuuming; no dry sweeping of demolition debris; walk-off mats at every boundary.
5. Scheduling. Sequence the dustiest work before or after the occupied floors' peak hours; coordinate with the tenant.

Point implications: the plan is a credit, but the practice also protects the prerequisite-level requirement to protect the building's indoor air during construction. A plan that exists on paper and is contradicted by the site log is worse than no plan.

Temporary heat: a gas-fired unit heater vents combustion products into the work area and adds water vapor. It must be vented to the exterior, placed so it does not draw from or exhaust toward the occupied floors, and never operated in a space that shares air with them. Combustion moisture in a gutted building also wets materials that will later be enclosed.

Rule set:

1. Building dry before materials. No gypsum board, carpet, or casework until the envelope is closed, the roof is watertight, and the interior is dry - verified by moisture content readings against a documented baseline, not by visual inspection.
2. Porous materials stored off the floor and off the slab, covered, on dunnage, in a conditioned and dry space. The parking garage is not a warehouse: it is unconditioned, humid, and full of vehicle exhaust.
3. Cold-weather protection. Do not run the temporary heater to dry a wet building; it adds combustion moisture and creates a temperature gradient that drives condensation inside wall assemblies. Heat the space properly and ventilate to remove moisture.
4. Wet trades before dry trades, and any wet work gets a documented dry-out period before enclosure.
5. Photograph and log the readings at each stage - the documentation is what separates a claim from an assertion.

Why this matters beyond the flush-out: the flush-out test is the moment of truth for volatile emissions, but moisture failures are structural and biological. A wall assembly enclosed wet grows mold that no amount of 14,000 ft³/ft² of outdoor air will fix, and the remediation will be done with the tenant in place. The owner's real exposure is not a failed air test - it is a two-year mold claim on two occupied floors.

Frame it for the contractor: early material delivery that has to be re-purchased because it was stored wet is not schedule savings; it is a change order with a delay attached.