Everything You Need to Know About Crawl Space Ventilation

By Shelley Frost

November 15, 2024

To ventilate or not to ventilate — when it comes to your crawl space, do you know which is better?

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Traditional practices encourage adding vents to crawl spaces to let outside air dry the space and keep moisture issues under control. However, traditional vents might cause more problems than good.

Does a Crawl Space Need to Be Vented?

Crawl space ventilation is up for debate among many builders, with some saying you need it and others saying you don't. The idea behind vents is to increase air circulation to prevent moisture buildup. The building codes in your area could determine if you need to install vents — some areas require vents in crawl spaces.

The problem with regular vents is that the outside air that enters your crawl space through the vents still contains moisture, regardless of whether it feels humid outside. Even though the ventilation system provides circulation, the humidity in the air could still allow mold growth, corrosion and rotting wood. It's often even worse if you live in a humid climate, and seasonal humidity changes also affect the situation. For example, many areas experience increased humidity in the summer.

Crawl space ventilation can also cause other problems. The vents could affect the heating and cooling in your home if there isn't good insulation between the crawl space and your main living area. Ductwork often runs through a crawl space. In the summer, hot air moves through the ventssurroundings the ductwork andcand warm up the air your AC has already cooled. In the winter, the cold outside air can cool down the heated air running through the ductwork. Your HVAC system may need to work harder to achieve your ideal temperature.

Is It Better to Encapsulate or Ventilate a Crawl Space?

An alternative to crawl space ventilation is encapsulating or sealing the area. Encapsulation is usually a more effective option for controlling the environment in a crawl space. Sealing the space can cut down on dust, pests and other debris you don't want inside your home. It also helps insulate the crawl space, creating a more consistent temperature. This cuts down on moisture in your crawl space, making the rest of the home feel hotter in the summer and cooler in the winter.

To encapsulate a crawl space, you seal up the vents and any other gaps or cracks that create air leaks. The crawl space receives insulation and a vapor barrier on the floor. This process is designed to keep moisture out of the crawl space and provide some temperature control in a space that isn't connected to the HVAC system.

How Does a Crawl Space Ventilation System Work?

In a traditional crawl space ventilation system, the builder adds vents to the walls of the space that lead outdoors. Regular vents don't have any mechanical components to them. They simply allow the air from outside to flow through the crawl space. However, they can also let other things in, including moisture, water and pests.

Some crawl space ventilation systems also incorporate exhaust fans to circulate air. Instead of relying on natural airflow, these systems pull in more outside air with the help of the fan. They also help push the old air out of the crawl space to keep the airflow moving.

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Is It Bad to Block Crawl Space Vents?

When deciding how to ventilate a crawl space, you might wonder whether blocking the vents is a good idea. Blocking crawl space vents could be harmful if you don't do anything to protect against moisture. With the vents blocked, no air moves through the space, which can allow more moisture to build up.

However, if you decide to encapsulate your crawl space, part of the process is blocking off the vents. In that case, closing off the vents is a good thing and a necessary part of the process. When you block the vents to encapsulate, you're also taking the additional steps of insulating the space and installing a vapor barrier.

Why Is Crawl Space Moisture Control Important?

Even though you don't spend time in your crawl space, you should still care about ventilation because the space has a significant impact on your home. Warm, humid summer air can cause moisture to settle into the crawl space, which can cause wood structures to rot. Rotten wood could cause a termite or carpenter ant infestation, which adds to the structural damage.

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