Help! We have built 30 houses total in the same subdivision and 2 houses have turned up with a bad sewer gas odor. They are not near each other and were built at different times of the year. The odor is only noticeable during warm weather when the windows are open. We have cleaned out chimneys,ductwork (looking for critters), and have done a smoke test. We don’t know the cause or what to do. Plumber has never had this problem before.