10/06/2026
COMMERCIAL MOLD BRIEF — Oct 5, 2026
When the HVAC is the leak
THE SUBSTANCE
Two public buildings in the news this September traced their mold back to the ventilation system itself, not a roof or a pipe. In both, humid outdoor air was coming in without being dried enough first.
- Platte City, MO City Hall (opened Nov 2023). Manually controlled outdoor-air dampers sat high above the drop ceiling, and staff didn't know they existed. Too much outside air came in, causing high humidity and condensation on the HVAC ducts. Summer 2025 brought stained ceiling tiles; summer 2026 brought visible mold. The city has spent $80,578 so far (testing, duct cleaning/replacement, antimicrobial treatment, sealing the dampers, portable dehumidifiers). Two permanent dehumidifiers for the incoming air are on order, follow-up testing is estimated at another $2,000 to $3,000, and the contractor recommended a $42,950 digital HVAC control system the city hasn't decided on yet.
- Chattanooga Police Services building (about 60 years old). Closed for nearly a year. The police chief told council that someone changed a system setting from 52-54 degrees to 72 degrees, so outside air was brought in without being cooled enough to pull the moisture out, then spread through the building. The Belfor remediation lead said there was three-quarters of an inch of mold in the ductwork, built up over decades, and that the rooftop make-up air system was, in his opinion, never properly installed. Employees reported severe allergic reactions. Council is weighing options from $9 million to $36 million.
- The standard behind it: ASHRAE 62.1 (since the 2022 edition, carried into 2025) tells designers to provide equipment and controls that keep indoor dew point at or below 60 F, in both occupied and unoccupied modes.
PLAIN SPEAK
Outdoor air in a humid summer is basically a wet sponge. A commercial system's job is to cool that air enough (supply air in the low 50s) to wring the water out before it reaches the rooms. Let too much of it in, or bump the setting up to 72, and the system just circulates muggy air everywhere, including inside the ducts. And the first warning signs are boring: a stained ceiling tile, a sweaty duct, a damp smell. Those are easy to swap out and forget, right up until they aren't.
WHY IT MATTERS FOR US
These are clients who don't think they have a leak, so they don't think to call a mold company. A property manager seeing ceiling-tile stains with no roof leak above them, or condensation on ducts and diffusers, needs someone who'll look past the drywall to where the moisture is actually coming from, test to define the extent, coordinate with their mechanical contractor, and verify afterward. Platte City shows the cost curve: small signs left for a year, then $80K and counting. It also shows a brand-new building isn't immune.
INTERNAL TALKING POINTS
1. "Any stained ceiling tiles where there's no roof leak overhead?"
2. "Do you know where your outdoor-air dampers are, and who's allowed to change setpoints with your HVAC vendor?"
3. "Does your building system log humidity or dew point, especially nights and weekends?" (62.1's limit applies in unoccupied mode too.)
4. Post-remediation verification is part of the job; Platte City budgeted follow-up testing before calling it done.
SOFT LINKEDIN DRAFT
Not every mold problem starts with a leak.
Two public buildings in the news this fall traced theirs to the ventilation system. In one, outdoor-air dampers nobody knew about let in more humid air than the system could handle. In the other, a setting change meant outside air was coming in without being cooled enough to pull the moisture out.
The early clues in both were ordinary: stained ceiling tiles, sweating ducts.
If you manage a building and you're seeing those with no roof leak overhead, it's worth asking where the moisture is really coming from. Happy to talk it through anytime.
SOURCES
Platte County Landmark, Sept 25, 2026: https://plattecountylandmark.com/2026/09/25/mold-cleanup-at-city-hall-tops-80000/
NewsChannel 9 (Chattanooga), Sept 29, 2026: https://newschannel9.com/news/local/safety-walkthroughs-not-complete-in-mold-infested-chattanooga-police-service-building
ASHRAE 62.1 Addendum e (60 F dew point limit, Section 5.12):https://www.ashrae.org/file%20library/technical%20resources/standards%20and%20guidelines/standards%20addenda/62_1_2022_e_20220930.pdf
Platte City has spent more than $80,000 addressing a mold problem at city hall that officials say was caused by excessive humidity and condensation from the building’s HVAC system.
