There are a number of reasons why sewer gases can enter a home. Perhaps one of the most common reasons is that plumbing fixtures and traps start to dry out. Plumbing traps have water barriers to stop sewer gases from escaping back into the home. If this dries out, there is no barrier to prevent those gases from entering the home. You could find this happening with periods of dry weather or with bathrooms that are not used often.
Some other reasons for sewer gas leaks are cracks forming in plumbing drains, foundations and ventilation pipes. If plumbing vents have been placed too close to air intakes, this can also cause sewer gases to enter the home. You might even find that the smell of sewer gas in the home is caused simply by the air flow around the building.
While these are some of the reasons why you might be smelling sewer gas in your home, is it something you should be concerned about? Depending on the levels of sewer gas in your home, this can cause a number of dangers. There is a danger of fire, explosion or even risk of asphyxiation from sewer gases displacing the homes oxygen. There is also the risk of hydrogen sulfide poisoning which could be lethal. Then there is the smell which is difficult to cope with. If you are worried about sewer gas in your house, its best to have the cause of the problem identified by a professional. The health and well-being of the homes occupants always comes first.
Devereaux Van Dyne, Certified Professional Home Inspector