Is It Advisable to Close Crawl Space Vents in Winter?

Sealing off the crawl space and blocking vents will help you beat back moisture that threatens to damage this functional space.

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If homeowners knew what effect the bitter winter cold and moisture have on their crawl spaces, they would block vents and seal up this area. A lot of homeowners overlook this to their detriment. The ugly truth is that vents aren’t useful in controlling moisture. While the cold winter air carries less moisture, it can still cause problems if airflow goes unabated. 

When winter arrives in Moberly, MO, you want to make sure the crawl space is well-protected against moisture and freezing temperatures. We’ll show you how, but first, let’s look at how venting contributes to crawl space issues and problems around the home. 

close and cover crawl space vents

Downsides of Crawl Space Vents 

By failing to seal your vents in winter, you’re setting the stage for these problems. 

  • Frozen/burst pipes. When temperatures drop, water in your supply lines will freeze. You can avoid this scenario by blocking vents and insulating the pipes. 
  • Higher heating costs. Since cold air flows unabated, your heater will be forced to work extra hard to create favorable conditions. The extra hours will translate into higher utility costs and less energy efficiency
  • Crawl space condensation. Contrasting outdoor and indoor temperatures cause the air to give up its moisture. Water droplets will form on your insulation and masonry block walls. 
  • Mold growth. If the winter is extremely wet, you’ll start seeing rapid mold growth and fungal spread. These organisms are harmful to your health. 
  • Stack effect. With air flowing unabated, the cold outside air will displace the warm inside air. And this cycle continues causing your home to cool off eventually. The stack effect also introduces dust, bacteria, and other pollutants in the crawl to the rest of your home. 
  • Wood rot. Your floor joists and beams will start soaking water from the air and attract wet rot spores. These microorganisms will attack your wooden beams and joists and weaken them. 
  • Musty odors. Mildew, decaying wood, and mold spores will release pungent smells in the crawl space, and these odors can move up to your home through the stack effect. 
  • Insect infestation. Termites are drawn to warm and wet crawl space. Moisture from the outside will be enough motivation to breed in the crawl space. 
  • Water damage. During winter, water freezes and expands, exerting pressure on the supply pipes running in the crawl space. Water may start leaking through joints or pour out via raptured sections in the pipe. 

Are Vents Useful in the Crawl Space? 

Numerous studies show that vents are actually detrimental to your crawl space health. These fixtures invite moisture, insects, and pollutants from the outside. However, some homeowners have been closing their vents in summer and opening them in winter. This approach doesn’t yield positive results. 

Some homeowners also think they can beat moisture by installing crawl space dehumidifiers. While these devices can reduce humidity, they won’t eliminate moisture completely, and that’s because the vents are open. Without proper covers, your efforts to dehumidify the crawl space will come to nothing. 

Block Airflow to Your Crawl Space 

You can avert moisture-related problems by closing up the vents using durable plastic vent covers. They’re easy to install, maintenance-free, and fitted with foam weatherstripping. Once in place, these covers create an airtight seal around the vents. What’s more, these rugged plastic vents are properly sized to find standard crawl space vent holes. And they’re resistant to moisture. Your home will stay fully protected from pests, humidity, and outside temperatures. 

Isolating the Crawl Space 

Once you block vents, go ahead and seal up the crawl space by covering the walls and floor with a heavy-duty 20-mil plastic vapor barrier liner. What this does is separate the crawl space from the cold and humid outside conditions. Waterproofing and insulating the crawl space also is a good idea to keep it safe and healthy. Be sure to schedule a free crawl space inspection and repair quote with the expert team at Foundation Recovery Systems before you embark on any sealing or waterproofing exercise. Our experts will check the crawl space and tell you what needs to be fixed or resolved before sealing up this space. We have the tools, experience, and expertise to do a flawless job.