Q, For the past two weeks, a strong foul odor has permeated our guest bedroom. We were sure an animal had died under the house, but the subarea has been thoroughly inspected and nothing was found. Each day, the smell seems to grow worse and soon will be unbearable. If nothing can be found in the house, beneath the structure, or in the surrounding shrubbery, what can we do?
A. Detecting the source of an elusive building odor can be challenging and perplexing. The best approach is to fully examine the immediate area while considering all potential causes.
A common source of noxious odors in homes is faulty venting of the drainpipes. Wastewater pipes are required to be vented to the outside of the building, usually above the roof, to prevent sewer gases from entering the house. When there are problems with wastewater venting, sewer gas odors inside the home can be very offensive. However, because you compare the stench in your guest bedroom to that of a dead animal, sewer gas may not be the problem.
If the cause, in fact, is a dead animal, and you haven’t been able to find the source in visible areas of the building, your next step is to consider all of the concealed spaces within the immediate construction. These would include the attic area, cavities within the walls, and the insulation between the floor joists under the house, assuming your floor is insulated. Rodents of various types often inhabit these areas, and odors can be intense when they die.
The attics in many homes contain rodent traps or poisons that were placed there recently or in years past. When mice or rats are killed by either means and are left to decay, terrible odors often result. Therefore, a careful search of the attic would be a good first step. In some cases, birds manage to enter an attic and are unable to find their way out, finally dying and decaying inside the building.
There are also instances of rodents dying inside the wall cavities, When this occurs, locating the problem by visual inspection is usually impossible. In those cases, it is helpful to find a home inspector who uses a thermal imaging camera. If the decay process is still taking place, thermal imaging can often be successful.
Another possibility is rodent nests in the floor insulation. Insulation provides an inviting habitation for mice, rats and other small creatures. If one of these has died, that could be the source of the odor. To explore this possibility, someone will have to crawl under the building, and thermal imaging again could make the difference.
Finally, there is another possibility, getting us back to the attic. A common inhabitant of that part of a building is bats. If you have never smelled the odor they can create without even dying, you don’t know what you’re missing. It’s enough to drive you out of your house.
Those are some of the most common answers to your odor mystery. So resume your search, and good luck.
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