A tenant on the fourth floor of a 40,000-square-foot office building in Auburn Hills filed a complaint that had nothing to do with temperature. They wanted proof the system was actually pulling in fresh outdoor air throughout the workday. The property manager pulled the original mechanical drawings, saw the rooftop unit had been sized correctly when the building went up, and figured that settled it. When we measured airflow at the intake three weeks later, the unit was delivering 165 cubic feet per minute (CFM) of outdoor air to a suite that Standard 62.1 from the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) requires 292 CFM for. A 43 percent shortfall had built up slowly enough that nobody noticed it happening.

How the Standard Sets Its Numbers

ASHRAE Standard 62.1, Ventilation for Acceptable Indoor Air Quality, sets minimum outdoor air ventilation rates for commercial buildings based on space type and occupancy. It has been the reference standard adopted into building codes across most of the country, including Michigan, for decades, and the Auburn Hills shortfall didn’t come from a new rule nobody had heard of. What changed after 2020 is how much attention building owners and tenants started paying to whether a building actually meets a standard that had been sitting in the code the whole time.

The standard sets ventilation rates as a combination of outdoor air per person and outdoor air per square foot of floor area, varying by space type, since an office, a classroom, and a gym have very different occupancy densities and pollutant sources. For a typical office space, that combination works out to 5 CFM per person plus 0.06 CFM per square foot of floor area. The Auburn Hills suite has 20 employees across 3,200 square feet, which is where the 292 CFM benchmark came from: 100 CFM for the people (20 times 5) and 192 CFM for the floor area (3,200 times 0.06). Meeting 62.1 means a system has to deliver that combined minimum continuously, under real occupancy, a bar few owners have actually measured their building against.

What Changed After 2020

ASHRAE published guidance during the pandemic recommending buildings increase outdoor air ventilation and upgrade filtration above minimum code requirements where systems could handle it. That guidance was framed as risk mitigation for airborne pathogen transmission, sitting on top of a baseline code standard that stayed the same. In 2023, ASHRAE released Standard 241, Control of Infectious Aerosols, which established a separate framework building owners can adopt for infection risk mitigation during public health emergencies. It sits on top of the 62.1 baseline as an added layer, and the baseline itself still has to be met underneath it.

That distinction matters. Meeting 62.1 is the legal minimum most Michigan commercial buildings must hit. Standard 241 is a separate, optional framework some owners are adopting proactively, often for tenant reassurance in office leasing or healthcare-adjacent spaces.

Why Most Buildings Do Not Know Where They Stand

Ventilation compliance is not something a building owner can eyeball. It requires knowing your system’s actual outdoor air intake rate under current operating conditions, which drifts over time as dampers stick, filters load up, and building occupancy or layout changes from what the system was originally designed around. A building that met 62.1 at installation ten years ago is not guaranteed to still meet it today if nobody has re-verified the outdoor air rate since.

Measuring the Intake Directly

A real ventilation assessment measures airflow at the outdoor air intake directly, using a calibrated instrument on site. That number reflects current operating conditions; the original construction drawings only describe what the system was designed to do on day one. The assessment then compares the measured rate against the occupancy and space type calculation the standard requires for the building as it’s actually used today. Where the measured rate falls short, the assessment identifies whether the shortfall comes from a mechanical issue, like a stuck damper or an undersized fan, or a design issue, like a system that was never sized to meet current occupancy in the first place.

Getting a Real Number for Your Building

Build an outdoor air ventilation assessment into your next major service visit. Delivered airflow drifts from the original design over years, the way it did in Auburn Hills, and an assessment is the only way to know where a building actually stands. The Auburn Hills fix turned out to be a stuck outdoor air damper and a fan speed adjustment, a $2,600 repair once the actual shortfall had a number attached to it. If you are fielding tenant questions about air quality, the answer they actually want is a hard number from a calibrated instrument: how much outdoor air is reaching their space per person. That is a conversation worth having with your contractor before a tenant brings it up first.

Common Questions

Does upgrading filtration alone satisfy tenant air quality concerns? No. Filtration and ventilation solve different problems: higher filtration removes particles from air that is already circulating, while ventilation brings in fresh outdoor air to dilute contaminants and replace stale indoor air. A tenant’s concern is usually better addressed by confirming both systems are working correctly.

How often should ventilation rates be reassessed? There’s no universal legal requirement dictating a schedule. In practice, we recommend checking outdoor air rates whenever occupancy or space use changes significantly, and folding a check into the periodic maintenance review otherwise. Dampers and controls drift gradually over years of operation, and a reassessment is the only way to catch that before a tenant does.

Is Standard 241 required for our building? It only becomes a legal requirement where a local jurisdiction has specifically adopted it, or where a building type carries its own public health mandate. Most Michigan commercial buildings fall into neither category, which means the answer is usually no. Adopting it stays a discretionary choice sitting outside what 62.1 compliance already requires.

Sources

ASHRAE: Standard 62.1, Ventilation for Acceptable Indoor Air Quality

ASHRAE: Standard 241, Control of Infectious Aerosols