The Inside Outside Guys: What's in your crawl space?

By Ken Calverley and Chuck Breidenstein
View Comments

Crawl space. The term conjures images of unknown creatures and the smell of molds.

Crawl space. That place below your floors that barely separates your home from the ground below.

Crawl spaces have a long history of being used where it was either too expensive or too difficult to dig a deeper foundation. The intention was to get the wooden floor of the home up off the ground, then provide fresh and constant air circulation through vents to minimize moisture build up and the molds that feed off wood and moisture.

It was a good idea 300 years ago.

Today it is a crazy notion to build a crawl space the way we, the industry, used to; no footing drains, no moisture or vapor barriers, constant outside air ventilation, no insulation, no conditioned air. A badly designed crawl space is often a source of contaminated, unhealthy, air in the home. It also creates cold floors in the winter and may contribute to damaging the floor frame.

A misplaced screen around a faucet provides an easy entrance for rodents to enter the crawl space beneath this home in Fort Worth, Texas, on Wednesday, September 23, 2009. (Ron T. Ennis/Fort Worth Star-Telegram/MCT)

The Guys like the concept of building a crawl space as you would a basement – just a little shorter. And there are still situations where a “short basement” makes sense. If you are building on a high water table and/or proximate to a large body of water, it may not make sense to dig deep. If you are expanding the house footprint, but don’t need more basement, a crawl space may make sense.

A properly designed crawl spacewill be at least “6 block”, meaning it will be at least 48” high on top of the footing. This provides enough “crawl” room to functionally install the house mechanicals like a furnace, ductwork, electrical items and plumbing pipes, while also getting the foundation deep enough to get below the frost line.

Historically, the main access to a crawl space may have been through a hinged section of floor – as such spaces were intended also to bring the “root cellar” directly under the home for easier access during cold winter months. Today we can enter the space through a “Bilco” type steel door system attached to the foundation. The Bilco system provides ease of entry and added security.

Footing drains leading to a city storm system or sump crock should be provided to intercept ground water.

Keeping with the “short basement” analogy, no vents will be installed in the crawl walls. Instead, the walls will be insulated and air sealed as will the exterior perimeter of the floor frame. The floor frame itself will not be insulated.

A good vapor barrier will be installed over the crawl floor and, if budget allows, a concrete floor will be placed in the space. Generally the minimum vapor barrier suggested is 6ml plastic, but far heavier materials will work even better and withstand some abuse over time if left exposed.

When all of these specifications are properly employed, the last step is to condition the air in the crawl. Conditioning the air accomplishes several things. Moving air through the space and combining that air with the rest of the conditioned air in the house minimizes the chances of high moisture in the crawl. It also reduces the chance of ever having molds grow in the space and having contaminated air in it.

A “comfort” benefit of properly constructing the crawl space is warmer floors while we also gain an “efficiency” benefit in heating and cooling costs.

Dale King from Foundation Systems of Michigan says it best; “ Encapsulating a crawl space provides lasting value for current and any future home owners.” The Guys agree.

For more home improvement advice listen to the Inside Outside Guys every Saturday and Sunday on WJR-AM 760  from 10 a.m. to noon or contact us at insideoutsideguys.com with your questions.

View Comments