Sewage smell in house

Hi, folks
Does anyone ran into a defect analysis inspection for a villa where the occupants complain from a bad sewage odor coming in and out every few days? It is not continuous but rather comes and go.

I went today and here are some facts that might give more insight:


  1. The smell always appearing in the Master bedroom/bathroom and it usually starts when they turn the AC on. Stays for 10 minutes then disappear.

  2. All water closets/fixtures are regularly used, so no dry traps

  3. The two sinks in the master bathroom doesn’t have P-Trap installed. It is a “Cup” style and the plumber that did the installation is arguing that they do not need a P-Trap as the floor drain has one?

  4. The vents pipes are extending well above roof surface and is way far from the exhaust fan pipe

  5. The basement “in the garage” has a room where the sewage manhole exist. When you open the door, you kind of smell the same odor.

Does this give any new insight o what can this be? Could the vent pipes be leaking somewhere into the walls? Will a smoke test help confirm that?

Any help is appreciated.

I’ll also post the same in the “general inspection” section to expand the ideas.

Thanks all

I encountered a similar situation recently. The smell occurred when I turned on the AC. The client noticed it as well. The homeowner mentioned he just paid $1200.00 to get the ducts and the evaporator cleaned.
(Showed me the invoice). After doing some investigation in the basement, I saw a small brown drip on the edge of the cold air return where the DWV pipe went though.(no, I didn’t do the lick test this time!)
I showed the homeowner and he got a pair of snips and opened up the return.

This was the problem. Homeowner got it repaired and I understand my client is purchasing the home.


Thanks, Joseph for sharing…Good catch.
In our case, the strange part is that the smell is not consistent. Sometimes they turn the AC on and there are no issue and sometimes the smell hits them. Not only that, but when the smell comes up, it usually stays for 10 min or so and then disappear ! Can’t ready put my hand on what could that be?

It seems AC related so I would check things like the condensate drain on the evaporator and anything that might affect supply air or return air to the master bedroom.

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this goes back over a decade on a 1 yr warranty & my reinspex weren’t cheap back then, made more on the reinspex than the original inspection

i am s stickler for closing door/off areas during insp

sewer gas smell @ laundry only occurred when the exhaust fan was on @ laundry & adjacent kitchen…yummy

i reported open the wall to thoroughly evaluate

gas leak detector (gld) identified leak @ cleanout/wall area

builder said loose cap @ cleanout, builder repaired w/tightening & Teflon tape

next week odor reoccurred

rechecked w/gld & odor was coming from the unsealed opening around cleanout, builder said we’ll repair w/caulk

next week odor reoccurred

reminded all of my original comment open the wall to thoroughly evaluate

oy, they finally complied & found an apparent brick tie fastener had penetrated/cracked the vent stack

weird shit happens

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