Explainers: where commercial odors come from and what to do

A floor drain that nobody uses can lose its water seal and let sewer gas into an office, shop or warehouse. Here is how to confirm it, how to keep it from happening again, and when the problem is bigger than a dry trap.

Sometimes every trap is full and the plumbing is sound, yet a suite still smells like sewer gas. On single-story commercial buildings the source can be a vent pipe on the roof sitting too close to the outside-air intake of a heating and cooling unit.

Most single-story commercial suites in the north metro are heated and cooled by a packaged rooftop unit. When the supply air smells wrong, the type of smell narrows down where to look and which trade to call.

In many multi-tenant buildings the wall between two suites stops at the ceiling grid. Above it, air, smoke and cooking odor move freely. Understanding that hidden space is the first step toward proving where an odor comes from.

Second-generation space, a suite left with the previous tenant's improvements, can save months of buildout. It can also carry years of cooking, smoke or chemical odor in ceilings, ducts and floors. Deal with that before the lease is signed.

Responsibility for a commercial odor usually follows the source: inside the suite, in a shared system, or in the building structure. The lease language decides the rest, so read it before arguing about it.

Cooking smell in a neighboring suite almost always has a path: a rooftop exhaust, a shared ceiling space or a pressure imbalance. Mapping the path comes before any cleaning or treatment.

A cooling coil removes moisture from the air, and that water has to leave through a pan and drain. When it sits, the smell reaches every room the unit serves.

Food-service drains collect fats and food solids that sour quickly. When an interceptor or line is overdue for service, the smell can reach neighboring suites and the parking area.

Fitness spaces combine heat, humidity and porous floors and mats. Persistent smell usually means moisture or residue is staying put, not that the room needs more fragrance.

Clinical spaces have drains, chemicals and waste rooms that can all smell. Because patients and staff are present, the first question is whether the odor is a nuisance or a possible health or safety concern.

Child care rooms have frequent spills, laundry, food and cleaning, so odor can come from many places. Because children are present, product choices and timing deserve more caution than in an office.

Smoke leaves a sticky film that works its way into porous finishes and the air system. Painting over it rarely holds, so the usual path is clean, replace what cannot be cleaned, then seal and ventilate.

Hail and heavy storms can open small leaks that wet insulation, tiles and drywall out of sight. Odor follows the moisture, so dry out the building first and treat the smell last.

Flex buildings mix offices, light manufacturing and storage under one roof. A chemical smell can come from a neighbor's process, a shared exhaust or stored materials, and needs a safety check before cleanup.

Fresh finishes release vapors as they cure. Planning ventilation and sequencing before staff move in usually matters more than any treatment applied afterward.

Cleaning, filtration, fogging and oxidizing methods solve different problems. Matching the method to the source and to who is in the building matters more than which one sounds strongest.

When a smell shows up after the building has been closed, the cause often lies in air handling schedules and dry fixtures, not in what staff did. Reading the timing helps find which.