I recently (2 months ago) purchased one home in a brand new 2 story duplex in Houston, TX. The master bathroom is on the second floor and has a separate room for the toilet. On a good day, the room will have a very strong mildew smell. On a bad day (maybe 1 day in 3 or 4), the room will have a strong stench of sewer that will often spread to other parts of the bathroom and master bedroom.

On occasion, we will notice similar odors in the downstairs portion of the home. The odor is faintly noticeable in very specific parts of a room (i.e. if you move to the right or left by a pace or two, the odor is not noticeable).

The builder’s recommended plumber has visited the house twice (unfortunately, the smell was not present at that time) without success. In addition, the builder’s pest control expert has confirmed that the smell is not the result of pest infestation. The HVAC folks have confirmed that the source of the smell is not the AC / heating system.

The builder himself has come to the house and smelled the smell. His carpenters removed portions of the bathroom wall (and also an adjacent closet wall). The smell was present behind the wall, but not source of smell was readily identifiable. Two toilets were removed and reseated with new wax rings (again this did not stop the smell).

Can anyone offer suggestions for locating the source of this periodic, but unpleasant smell? I have heard of smoke tests. Are these effective?