Crawl Space Ventilation: When to Open and Close Vents

Did you know that mold destroys more wood than fires and termites combined every year? Although mold is a slow killer, more raw materials become its victim.

The main cause of mold in outdoor and indoor air is moisture. If you have a crawl space area that is part of the foundation of your home, you might be familiar with how difficult it is to keep moisture out.

If your crawl space becomes the victim of mold, you’ll be risking irreplaceable home damage and a dangerous home environment. You can diminish this risk by optimizing your crawl space ventilation.

Read on to learn about crawl space vents and other methods for preventing moisture.

How Does Crawl Space Ventilation Work?

In order to optimize crawl space ventilation, you need to understand how the process works.

A foundation with a crawl space in it is more common in warm, moist climates. The advantage of raising the structure includes avoiding moisture.

When air rises in the home, it is carried from the air that was once in the crawl space. If moisture and mold spores were in the crawl space air, those airborne particles can make their way into your home.

The Most Destructive Element: Moisture

For crawl spaces, the most destructive element is moisture. Moisture bears responsibility for multiple problems that occur in a home such as different mold and mildew strains, and wood rot.

If moisture is not dealt with promptly, the house can come completely down in a short period of time. In fact, a leak or spread of the flood can happen within the first 24 hours.

If you leave water damage for too long, your insurance might not cover the damage it causes. Not only that, but the longer you leave water damage unattended, the more it will cost you to repair.

To combat the issue of moisture in the crawl space, it is best to use light, heat, and airflow. Promoting good airflow is your best bet as it is difficult to bring light and heat into a crawl space.

You can try DIY methods of crawl space lighting, but without professional help, it might be hard for your efforts to be successful.

Building codes require that crawl spaces be vented to avoid moisture damage that can cause rotting joists, beams, and flooring. Airflow to help keep the spaces under a home dry are provided by screened vents inserted into the foundation.

Types of Crawl Space Vents

There are standard requirements for ventilating crawl spaces, one including the types of crawl space vents that can be used. Each vent should be at least one square foot and made up of certain materials such as:

  • Sheet metal plates (expanded or perforated)
  • Cast-iron grating or grill
  • Extruded load-bearing brick vents
  • Hardware cloth
  • Corrosion-resistant wire mesh

A ground vapor barrier is another allowable option if the type has moveable louvers. If you don’t know the different types of crawl space vents or aren’t aware of the kind you have, a professional can take a look and let you know.

Unventilated Crawl Spaces

Although it is highly recommended to have vents on the side of the house, some provisions allow unventilated crawl spaces.

These provisions were put in place for homeowners who want to prevent thermal heat loss or prevent vermin and insects from getting into the crawl space. Builders can create non-vented crawl spaces through these procedures:

  • Mechanical circulation of the air
  • Use of an air-circulating device that will move at least 1 cubic foot of air per 50 square feet of the crawl space area
  • The crawl space floor area is completely sealed with a vapor-retarding material
  • Vapor retarder edges must be lapped against the inner walls of the foundation
  • Crawl space walls are insulated to the appropriate R-values for the surrounding area’s climate

If your house was built with these procedures in mind, you don’t have to worry about when to open and close crawl space vents. However, most homes find use in crawl space vents and should follow the advice below.

contractor conducting crawl space maintenance

Should Crawl Space Vents Be Opened or Closed?

The answer to, “should crawl space vents be opened or closed?”, depends on the season. During the summer, opening air vents can bring in heat to prevent moisture buildup that encourages rot and mildew.

Because the air is drier in the winter, should you open crawl space vents? Most people prefer to close vents in the winter so that the pipes in the crawl space don’t freeze.

If you have a dirt floor crawl space and keep your vents open throughout the year, the floor will become a never-ending source of moisture. Even if the surface of the dirt looks dry, a few inches down the Earth is moist.

How to Close Foundation Vents in the Winter

Closing foundation vents for the winter is simple if you plug them up from the outside with foam blocks. There are also crawl space vent covers for winter made specifically for this reason.

You’ll need to remove these plugs during mild spring weather to prepare for the summer season. During removal, ensure the vent screens are still intact so that insects cannot make a home under your house.

If you are asking yourself, “should I close crawl space vents?”, the answer is yes. How often you do it depends on the weather conditions in your area. Yet, keeping water out of the crawl space isn’t as simple as opening and closing vents

Additional Tips on Keeping Water Out of Your Crawl Space

Unfortunately, not all builders will consider the precautions necessary for keeping water out of a crawl space. Although ventilation can help with a majority of water problems that occur around the foundation, consider these tips as well:

  • Creating positive surface draining around the home
  • Opting for working gutters and downspouts
  • Installing generous eave overhangs

In addition to the things you can do on the outside of the house, focus on the inside as well. A persistent leak that started in the home can keep the crawl space wet enough to grow fungus or attract pests.

Although less likely, it is also possible for standing water to foster deadly microorganism growth. This is why having positive surface draining is so important.

You can also install a crawl space vent well to prevent water from getting into this area of the foundation.

When the crawl space is too warm or humid, fungus will start growing. This is more likely to occur if the surface of the crawl space is slightly dirty or porous.

Crawl Space Encapsulation

Although not stated in the crawl space ventilation requirements, some homeowners choose to encapsulate the crawl space. This involves adding air from the HVAC system.

If you have a duct system already installed, this method is inexpensive and easy to complete. The air from your HVAC system will help dry out the air in the crawl space area.

Some homeowners prefer to seal their crawl space vents throughout the year to allow heat and air conditioners from their HVAC system to seep in. If you plan to go with this option, it is best to be sure about it beforehand.

If you have a properly sized air conditioner, this method can work well in the summer. You’ll be able to keep the humidity relatively low. During other seasons, a home with an oversized air conditioner won’t work well with this method.

Dehumidifier Installation

Installing a dehumidifier in the crawl space only works after the space has been encapsulated.

The difference between a standalone humidifier and using your HVAC system is that the dehumidifier is controlled by the condition in the crawl space and not the house above it.

A few drawbacks of installing a dehumidifier include buying it as an additional piece of equipment and maintaining it. You’ll also run into problems if your drain fails because it can lead to bulk water in the crawl space.

However, the benefit of having dry air in your crawl space often outweighs the cons. This option tends to work better than a crawl space ventilation fan as well.

What Is the Best Solution for Your Crawl Space?

Crawl space ventilation is important but there are multiple ways to keep the air dry. The method that works for your home will depend on climate conditions and the details of your crawl space.

In drier climates, opening and closing vents can work throughout different seasons. Yet, crawl space encapsulation remains the most popular method, and for good reason.

Not sure what solution is best for your crawl space? Contact us for a detailed inspection. We go down there so you don’t have to!


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