Demystifying Crawl Spaces: Crawl Space Choices in Southern Appalachia

If you are confused about the best method to control moisture and humidity in your crawl space, you are not alone.

We recently visited Marcus’ 84- year-old independent father, Helmut. It quickly became apparent that there was a substantial mold issue in his home, as his baseboards and back bedroom closets had some decent growth.

A trip to his crawl space unveiled the obvious culprit: not only had he blocked off his vents with fiberglass insulation, he had a decent plumbing leak. His home is only 12 years old.

A pair of curious neighbors came over to see what was up. Helmut told them that we were discussing options for controlling the humidity, since he had sealed off his crawl space vents. The neighbors made eye contact with us.

“Helmut, those vents are designed to open and close with the seasons; they are not meant to be sealed shut,” they offered. We nodded in agreement. Helmut replied, “Oh, no, not anymore, the new code says that you are supposed to seal the vents permanently.” We shook our heads, signaling to the neighbors that they should not heed his advice.

Encapsulated crawl space. HARPER ROBINSON PHOTO

By the way, Helmut was a mechanical engineer for 40 years and his son owns a company that encapsulates crawl spaces — i.e. he is someone with knowledge and resources that could have helped him make a better decision. But he had read somewhere that code now requires that the vents are sealed, and so crawled down there one day to do the job, unbeknownst to us.

The takeaway of this story is that a lot of people are confused about their crawl spaces and misinformation is easily passed along that can lead to damage to a home.

So, crawl spaces are confusing and some of them have frustrating mold and moisture issues. Also, some of them are haunted. OK, we are kidding on that last part (actually, no, we’re not).

The good news is that there are ways to control and eliminate moisture problems, so the space is less problematic. (Note: if your crawl space is haunted, don’t call us.)

Whether you do the work yourself or hire a professional, here are some notes to consider, so that results do not do more harm than good.

Crawl spaces generally fall into two categories: vented and unvented.

Vented crawl spaces — the traditional method — use foundation vents to allow moisture to escape the crawl space. The foundation vents should be opened in the summer and closed in the winter. The current building code allows this method of crawl space as long as there is a vapor barrier, which is just thin plastic on the floor. Oftentimes, homeowners in this climate discover that this method is not effective in eliminating humidity issues and can actually make the humidity worse. Studies have shown that open vents in the summer allow more moisture in then out due to high humidity in the Southeast region. Humidity can lead to mold, other funguses, wood decay and poor indoor air quality. (And ghosts … just kidding.)

Unvented crawl spaces are often called “conditioned,” “sealed,” or “encapsulated” crawl spaces. We like to use “encapsulated” because we think it has the nicest ring to it. The current building code also allows for this second variation of the crawl space. This method eliminates or blocks foundation vents; blocks out ground moisture with a heavy-duty, thick, plastic, sealed membrane; and incorporates a way to dry the air with either a dehumidifier or an HVAC supply vent or indoor air supply. A professional-grade dehumidifier is most commonly used. The building-performance industry has determined that this is the best method to address a new or existing crawl space in our region.

We’ve really got you on the edge of your seat right now, eh?

So, back to Helmut. He only sealed his vents, which trapped moisture in the crawl space. He did not control the ground moisture or condition the air with a dehumidifier, so he was on the right track to an encapsulated crawl space but missing two very important parts.

There are many ways to encapsulate a crawl space and many companies that do it. The basic tenants are: stop outdoor air from entering the crawl space; install a strong, sealed, vapor retardant membrane on the floor, walls and support piers of the interior of the crawl space; and condition the air so that it is dry enough to not support mold or fungal growth. There are lots of YouTube videos that will give you a good visual idea of what the finished product will look like.

There are a couple of final tidbits to consider.

If your only issue is humidity, an encapsulation will do the trick. However, if there is standing water in your crawl space, you will need to take further measures to address this. Make sure that your gutters are not overflowing and are diverted away from your house. Still have water intrusion? Is the slope around your home directing water toward the foundation? If so, exterior landscape grading may be needed. Darn, there is still standing water? As the final touch, you may need to install a sump pump that collects any excess water and pumps it outside.

It’s also important to note that once you have encapsulated, you can’t just close the door and forget about it. Routine maintenance is a must to make sure the dehumidifier, monitoring equipment, and sump pump are functioning properly, and that the sealed membrane is intact.

Oh, and don’t worry about Helmut. The plumbing leak is fixed, and we have since encapsulated his crawl space, properly sealed his vents and installed a dehumidifier down there to control the humidity and prevent mold.

Sara Sabol and Marcus Renner own Conservation Pros, an energy-efficiency retrofitting firm in Asheville. They have been encapsulating crawl spaces and improving the efficiency of homes and businesses since 2007. Connect with Sara and Marcus at

You can also view this article as it was originally published on page 55 in the 2019-2020 edition of the directory.