Is a Crawl Space Vent Really Useful in Cooling the Home?

Do not vent your crawl space

Crawl spaces are a common feature in many St. Louis, MO, homes as they’re cheaper to install than full basements, yet more functional than slab foundations. Unfortunately, these spaces can foster moisture problems.

Building codes and conventional wisdom require crawl spaces to be ventilated from the outside to control moisture buildup and reduce damage within the space. On the contrary, recent studies show venting the crawl space just does the opposite.

The History of Crawl Space Vents

Should I vent the crawl space or not? Before we can answer this highly debated question, you need to understand why crawl spaces have vents in the first place. Before the discovery of fiberglass insulation and air conditioning, homes (especially those with crawl spaces) used to get really hot and humid during summer.

Venting was fronted as a way of encouraging air circulation in the crawl space. During the hot summer months, homeowners would open up their vents to let in fresh, cooler air from outside to circulate in the crawl space, ultimately cooling the rest of the house. 

Are Crawl Space Vents Effective?

Although crawl space vents are mandatory in many areas, and the intentions behind them are good, the logic behind vented crawl spaces is faulty. The air inside your crawl space is cooler and more humid than air from the outdoors. So, if you open your vents, the warmer, more humid air outside gets into the crawl space and introduces moisture. 

Cons of Venting Your Crawl Space

Various tests and studies conducted by building scientists show that ventilated crawl spaces do little to keep out moisture. Instead, they do the opposite, which is draw in more moisture and raise humidity. This results in various unpleasant issues such as: 

Water Damage

When outdoor air enters your crawl space, it raises humidity levels, causing condensation on surfaces like your floor joists, pipes, and ductwork. Over time, this consistent moisture buildup leads to water damage, wood rot, and mold growth. 

Poor Air Quality

Naturally, the air from your crawl space flows into the living areas of your home. And it carries with it mold spores, moisture, and anything else that is airborne into your home. This natural upward movement of air is known as the stack effect. Home Energy Magazine estimates 40% of the air you breathe originates from the crawl space. A ventilated crawl space causes the stack effect, a continuous cycle that can cause myriad problems for your household. 

High Energy Consumption

When outdoor air gets into the crawl space, it not only bumps up high humidity levels but it also significantly increases your home’s energy costs. A study by Advanced Energy shows closed crawl spaces (insulated spaces without vents to the outside) can significantly improve moisture control and bolster energy savings

Sealed Crawl Space Vents

While the IRC allows people to create unventilated crawl spaces, it does so on the condition that homebuilders mechanically circulate air between the upper conditioned area and the crawl space. To nip moisture issues in the bud, we encourage you to seal the crawl space properly.

One common way of doing this is encapsulating the crawl space with a plastic vapor barrier. Done properly, this waterproofing method locks out moisture from the crawl space. Some of the products your contractor might use to bolster waterproofing include water removal devices like interior drainage and sump pumps.

 Once you seal up your crawl space, you’ll enjoy the following benefits:

The benefits of encapsulating your crawl space far outweigh the costs. So it’s well worth the effort. If you’d like to know how your local crawl space contractor in St. Louis, MO, will deal with moisture, schedule a free crawl-space inspection today!


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