How is my Crawl Space affecting my Indoor Air Quality?

According to the National Association of Home Builders, 65% of new homes in 2020 were built on slab foundations, 22% had a full or partial basement, and 12% had a crawl space.  From their statistics since 2000, it’s clear that slab foundations are increasing, while basements and crawl spaces are decreasing.  From an indoor air quality perspective, we have to admit that’s a good thing!  We found a lot of other pros and cons about slab foundations, and if you are building or buying a home and have a choice, you should investigate the differences.

Slab foundations became popular in the 1950’s; before that, most homes were “raised” with a crawlspace or set over a basement.  Crawl spaces did their job to keep the main living area “off the ground”, ie. not in direct contact with the earth, and they accommodate floor plan renovations more easily than slabs because of easier access to plumbing.  However, crawl spaces typically are partially sealed off, and very contaminated with dust, mold, bacteria and stale air.  What you did not know about crawl spaces may be the most harmful of all: “Approximately 50% of air on the first floor of your home comes from your crawl space.” (  How can this happen?  Due to the stack effect which affects virtually every building on the planet, warm air rises through the house and is replaced by cooler air from outside, through leaks in the lowest parts of the home.  If you have a crawl space that is partially open to the outside, you may even place a pinwheel or light tissue in the crawlspace opening on a still (non-windy) day, and see if the air currents are blowing into the crawlspace of your raised home.  Fresh air from outside will be drawn into the crawlspace, pick up dust, mold and bacteria (not to mention musty or animal smells), and infiltrate your home through leaks in the flooring.  Gross!

If you can’t or won’t investigate the condition of your crawl space first hand, find a foundation expert and ask them to conduct a thorough inspection (with photos).  Knowledge is the first step to preventing or remediating the problem!  Here’s what they may find:

  • Flooding.  Just like any other ground that floods, if water enters your crawlspace, it can pool and remain for weeks or months, depending on the environment and soil composition.  How about living over a stagnant puddle?
  • Moisture damage.  Moldy and rotten timbers are a consequence of constant water contact and high humidity.
  • Insect damage.  Termites can thrive in even lower moisture zones, and without proper termite prevention like physical barriers, they can do a lot of damage.  The shredded wood creates even more dust under the house.
  • Animals and animal damage.  There are several harmful aspects of animals living in the crawl space under the house.  For one, their feces can carry virulent diseases like hantavirus (from rodents).  Then, unfortunately they may die under the house, with accompanying death smells and a bacteria-laden carcass… Third, they may actually undermine the foundation with burrows.  Did you know that groundhogs can seriously impact your home’s foundation, causing sagging floors and major structural problems?
  • Damaged and missing insulation.  Exposure to water, insects and animals all results in deterioration of insulation on pipes, ducts and subfloor, so that the essential systems and floor itself are exposed.  

If you have a crawl space and want to improve indoor air quality, don’t miss this opportunity to take a step in the right direction by hiring a trusted professional to do an inspection, and then get several bids for remediation.  Most foundation companies will recommend a combination of the following to resolve these issues (from

  • Encapsulation is a method of sealing off the crawl space from the surrounding elements.  It involves closing crawl space vents, installing a vapor barrier so that moisture from the ground does not intrude, and installing a dehumidifier.
  • Insulation is important to prevent condensation and resulting mold issues.  Damaged insulation should be replaced and missing insulation should be installed.
  • Sump pumps are necessary if standing water has been a problem in the past, and to remove condensate from the dehumidifier.  
  • Repair of sagging and damaged joists and supports.

It may seem like a daunting task, and these tend to get postponed until things get really bad.  If you don’t know the condition of your crawl space, we want to encourage you to take a first step of inspection, which many companies do for free.  If remediation is required, call several more companies for inspections and quotes, and research their work.  When the work is completed, you will have the comfort of protecting your largest investment (your home) and increasing your air quality at the same time.  It’s hard to overestimate the cost of a less humid, healthier, fresher home!