Internitant sewer gas odors in commercial building

Received a call from a Realtor I work with on intermittent sewer gases in parts of their building but not the third floor of three floor structure. Here is the dilemma:

  1. Can smell sewer gases in the lower floor (1/2 below grade, like English basement) sometimes during summer months and floor above. Never in the third floor.
  2. Can smell the odor in the lower floor but not the floor above at times, mostly in summer months.
  3. Can smell odor in lower floor only, more in summer months.
  4. City has been contacted, ran lines to check out sewer nothing blocking and traps appear clean. Not their problem says the City.
  5. Plumbers have been called with same results, nothing found.
    I mentioned that blocked vent piping could be a cause but the Realtor could not remember if the plumbers checked this.

What could be the cause? Any and all help is appreciated.

I have had similar occurrences in commercial buildings with restroom floor drain traps that have dried out allowing sewer gases to enter. Try pouring 3-4 cups of water in all restroom floor drains, wait a day and see if that helps. If so, teach the cleaning crews to do this once a week or so.

I did some work in a commercial building and saw the plumber attach a AAV for a bathroom vent and it got buried in the wall behind the Sheetrock.
I asked him what happens if the valve fails and he just shrugged his shoulders and said he’d be long gone by then.

I’m wondering if a thermal scan would locate any pipes that may be in the wall??

Need to do a smoke test to locate the sewer gas source unless something obvious such as a dried out trap can be found.

I’ve found a variety of sources using smoke, including nails driven though pipes, ABS joints never glued, corroded out or rusted through pipes, you name it.
One time a house had been converted to an office and they just sheet rocked over the bath tub, leaving the faucet and drain untouched.

Never had a plugged vent cause an odor.

One of the vent stacks may be cracked inside the wall. I had this problem about 20 years ago in a resturaunt i owned. We found it by pouring cinamon extract down the stacks up on the roof. Pour some down, if you can smell it, you have a cracked pipe somewhere.

dry floor drains is is very common in comm bldngs.

Dennis, follow instruction given by Michael, most likely dried out traps . . . out here in the desert it’s very common.

The problem is now intermittent due to pressure changes in the building due to wind, mechanical ventilation and stack effect all changing the pressure regimes constantly. The smell may ocur when a negative pressure occurs in the area where the problem plumbing is located.

Use a blower door to depressurize the area of the buildig where the smell is and you should be able to locate the source pretty quickly if its from an open/cracked DWV pipe.