The title of this post is a question we are regularly asked. Quite frequently the answer to the question actually lies underneath of the home. Something many people don’t realize is that approximately fifty percent of the air you breathe on the main floor of your house comes from the crawlspace. This is because of something known as stack effect (a great picture and explanation is available here), which basically means that as the heated air in your home rises and escapes, a vacuum is created that sucks cold air through the crawlspace. (It can also contribute to cold floor syndrome.) As that air circulates into your living area, any odors from rodents, moisture or garbage below could be to blame for your house’s unpleasant aroma.

Another source of a home’s bad odor can be the result of crawlspace pest infiltration. Once inside the space, rodents love to nest and tunnel through the home’s insulation. Not only do they destroy the insulation’s R-value by compressing it, but they also soak it in waste creating a very strong odor. If you look underneath your home and see droppings on the vapor barrier, it is a good indicator of infestation and a very likely source of malodor. Removing the soiled insulation and sanitizing the space as part of a crawlspace cleaning job would greatly improve the home’s scent. It should also be noted that rodents sometimes carry dangerous diseases like Hantavirus and King County Public Health Department has indicated that exposure to rodent waste can trigger asthma attacks. If your crawlspace needs cleaning, confirm that the professionals you hire can do the job in a safe and sanitary manner and ensure that they offer rodent exclusion to prevent the rodents from returning to your newly cleaned crawlspace.

In a previous post about insulating for warmth, we explained how most crawlspaces in the Pacific Northwest are vented to the outside of the home. The purpose of the vents is to move air in and out of the crawlspace, however temperature fluctuations can create moisture causing mold, fungus, and other toxins to grow, none of which contributes to a great smell indoors. The moisture can also be particularly problematic for people with mold allergies.

Finally, garbage and debris are often found in crawlspaces and are leftover from the structure’s original construction. This is problematic because it can collect mold and fungus creating its own aromas. Further, garbage and debris are attractive to rodents and wood destroying insects.

Obviously, not all odorous homes can look to the crawl space as the source of the problem. Our homes become unclean from daily activities like cooking, bathing, breathing, washing clothes, pets, trash, and bringing in toxins from outdoors (read about how your shoes could be making you sick in this post). Without regular cleaning and proper ventilation, your home is likely to be a honk. Regularly airing out your home as part of your cleaning routine can help get rid of stale air. Some green cleaning tips for common household smells is available on This Old House.