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Vented Vs Unvented Crawl Space

With winter just around the corner, you may be considering getting a head start in keeping your home safe and comfortable.

Some homeowners prefer sealing off crawl space vents all year to prevent elements in the summer, heat loss in the winter, and moisture build-up that could lead to mold growth.

Others, however, prefer opening and closing the crawl space vents with seasons. But is there such a thing as a “right or wrong answer” when it comes to vented vs. unvented crawl space?

Vented Vs Unvented Crawl Space

Crawl Spaces Explained

As air rises in your home, it moves together with the air that was previously in the crawlspace. This includes moisture, mold spores, and anything else that may be airborne down there.

As this air moves upwards, replacement air is drawn through the vents. This replacement air consists of unconditioned air that enters through vents and other leaks. The resultant natural upward air movement is referred to as the stack effect- just like how a chimney works.

That means whatever is in the air at the lowest point of your home eventually streams up into the living space. Nearly half of the air homeowners breathe on the first floor comes from the crawl spaces.

Consequently, a dirt crawl space with open crawl space vents is a never-ending source of moisture. Even when the dirt surface appears to be dry, digging down a couple of inches uncovers moist air which is constantly released into the crawl space.

Moisture leads to mold growth, musty odors, and eventually structural damage, not forgetting that insects and elements love moist environments. Moisture also leads to increased energy costs as it ruins houses by creating a hospitable environment for mold and insects and other fungi.

Three things that destroy organic materials such as wood or insulation are water/high relative humidity, heat, and ultra radiation. Among these, water is said to be the most damaging.

Seal Off Crawl Space vents

With that being said, properly sealing your crawl space and removing the moisture from the ground and air can be an effective solution that helps maintain a mold-free and insect-free zone. This can lead to a more energy-efficient and healthier home.

Note that to avoid moisture’s adverse effects, a crawlspace should be completely sealed and isolated from the ground as well as the humid outside air. One effective method to lower crawl space humidity is by installing a proper crawl space vapor barrier system.

This generally involves installing a 20-mil 7-ply sandwich of high and low-density polyethylene with polyester-cord reinforcement on the dirt floor that is extended and fastened to the wall. The reinforcement lining should be treated with an antimicrobial finish that combat mold and mildew growth under the crawl space liner.

In other cases, a high-performance dehumidifier air filtration unit might be necessary for the crawl space to make sure humidity levels stay under 50%. It’s always best to consult your HVAC contractor to make sure crawl space venting is sufficient.

Open and Closed Crawl Space Vents Seasonably

The next option is to open and close crawlspace vents seasonably. Building codes usually require working vents in the crawlspace so that outside air can circulate under the floor in the summer to prevent moisture build-up.

During winter when the air is drier, the vents are closed to minimize the chances that the pipes in the crawlspace might freeze. So another answer is to open and close the crawl space seasonably, rather than sealing off the vents altogether.

How to Open and Close Crawlspace Vents

If you choose to not seal off crawl space vents year-round, the easiest way to close your crawl space vents for the winters is to plug them from the outside with foam blocks made purposely for crawl spaces. Then remember to remove the plugs when the weather turns milder in the spring.

As you do so, make sure that the crawl space vents screens are intact to prevent insects and rodents from making nests under your home. You could also decide to go with automatic vents, which are meant to work without electricity. These types of vents open at approximately 70 degrees and close at about 40 degrees.

Vented to Unvented Crawl Space Crawl Space

When converting a vented crawl space to an unvented crawl space, all of the vent openings, air sealing as well as insulation are installed at the exterior walls rather than at the outside of the floor above.

That means the crawl space becomes part of the conditioned space of the home. This creates a temperature space for heating and cooling equipment and even ductwork located in the crawl space. That means it will last longer and operate more efficiently.

As mentioned before, sealing off the vents, insulating the walls, and covering the ground with a vapor barrier that extends to the wall also helps to reduce potential moisture problems by keeping out humid outside air as well as moisture vapor from the ground.

How to Deal with Moisture or Mold in the Crawlspace

If you’re experiencing mold in your crawlspace, there are various approaches you can look into for dealing with the problem. Some of these solutions are as simple as installing a crawl space vapor barrier, maintaining the grade of your landscaping, or properly guttering rainwater away from the property.

Besides, there are different types of insulation you can consider. For instance, you can insulate your unvented encapsulated crawl space with closed cell spray foam. It performs as a moisture barrier when applied to at least 1-1 ½” thickness.

You can also go with fiberglass insulation, which is suitable largely for vented crawl spaces. Fiberglass batt or roll insulation is the most traditional method, but it’s a cost-effective way to insulate your property. Having that said, a crawl space service expert may be necessary to help fix the issue.