Does a Crawl Space Need To Be Vented? (6 Reasons Not To)

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Recently, a heated argument arose about the natural ventilation of crawl spaces.

Some old-school construction workers still abide by the old rules. However, new construction trends and research advocate sealing all vents in crawl spaces.

So, does a crawl space need to be vented?

This article outlines both sides of the argument. It discusses the benefits of having unvented crawl space and explains the mechanisms of the automatic vents and the circulation fans.

Are Crawl Spaces Supposed to Be Vented?

What would you do when a room gets stuffy? Simple! Open the window; isn’t that your first reaction?

That’s the exact rationale behind installing vents into a crawling space. For a long time, people believed that vents would allow fresh air to enter and replace any stagnant or stuffy air.

Many construction builders advocated that natural ventilation would help prevent mold, odors, and other pollutants. Interestingly, this theory is no longer valid, thanks to the new trends in building science.

Scientists argue that vents in a crawling space aren’t the best option to clean up the air. On the contrary, the outside air is often unsuitable for venting crawling spaces.

6 Reasons You Shouldn’t Install Crawl Space Vents

Scientists have shown evidence that air circulation through vents doesn’t eliminate problems, such as mold and humidity. On the contrary, natural ventilation may be one of the causes of these problems.

They now believe that vents do more harm than good in crawling spaces. Here’s why:

1 – Increased Moisture and Humidity

Remember how the main reason for installing vents is to prevent the occurrence of mold? This thought turned out to be wrong.

Fresh air always carries moisture. In other words, vents will allow moist air into the crawling space. This increased humidity level is the primary cause of mold in crawl spaces.

2 – Unbalanced Heat

The temperature inside your crawling space is typically lower than that of the air outside, especially in summer.

Vents allow the hot air outside to roam freely within your crawling space. Such temperature variation causes mildew, mold, and even wood rot.

3 – Dust

With natural ventilation, you can’t control what enters your space with the air. By definition, crawling spaces are closer to the ground than any other part of the house.

In this sense, you should expect dust particles and other pollutants to enter your space with the air circulating through the vents.

4 – Radon

Originally, builders chose venting crawl spaces to reduce radon gas levels in the air. However, in most cases, these vents aren’t enough to get rid of radon.

Instead, experts recommend other more effective radon reduction systems that work best in sealed spaces.

5 – Unwelcome Guests

Vents in a crawling space can be an ideal space for rodents, pests, and insects to enter the house. After all, they can let in more than fresh air.

In fact, if left unscreened, these openings can be wide enough to fit a large rodent, which settles in your rarely-visited crawl space.

6 – Utility Bill

Unvented crawl spaces help you save up to 18% of your utility bill. Preventing the temperature fluctuation in your crawl space can decrease your energy use.

In addition, sealed unvented crawl spaces don’t allow air to leak into the house. That makes the temperature of the crawl space close to that of the house.

Do You Have to Vent a Crawl Space?

Not anymore! In the past, the International Residential Code (IRC) required venting your crawl space. However, now builders are given two options:

1 – Building Ventilated Crawl Spaces

Section R408.2 of the IRC regulates the installation of vents in your crawl space. The IRC states that each vent should be at least 1 square foot.

Moreover, every screening material requires a certain minimum thickness. For instance:

• Expanded sheet metal plates: 0.047 inches or more.
• The corrosion-resistant wire mesh: at least 1/8 inch thick.
• Perforated sheet metal plates: above 0.070 inches thick
• Hardware cloth wire: not less than 0.035 inches.

Other allowed materials include:

• Extruded load-bearing brick vents.
• Cast-iron grill or grating.

2 – Building Unventilated Crawl Spaces

The third section of the IRC (408.3) allows building an unventilated crawl space after performing specific procedures, including:

Mechanically Circulating Air

The IRC requires installing a mechanical device to circulate the air between the crawl space and the air-conditioned area above it.

This device should be able to circulate at least one cubic foot of air for every 50 square feet of your crawl space.

Sealing the Floors and Walls

The code also necessitates sealing the entire floor area of your crawl space with a vapor barrier.

In addition, it requires wrapping the edges of the vapor barrier around the crawl space’s inner walls.

You should seal the seams. Ensure lapping every separate sheet of barrier that overlaps with others for at least six inches.

As for the walls of your crawl space, you’re required to insulate them to suitable values according to your regional climate.

How Many Vents Are Needed in a Crawl Space?

If you opt for a ventilated crawl space, the IRC also dictates the number of vents according to the area of your space.

Chapter four of the code states that there should be at least one square foot of vent space for every 150 square feet of crawl space.

For instance, you should install about six feet of vent space in a crawl space of about 900 square feet.

Fortunately, you can divide this vent space anywhere you want. You can go with six different one-inch vents or three two-inch vents.

Vents for a Sealed Floor

If you’ve sealed the floor of your crawl space with an approved vapor barrier, the IRC requires you to install only one square foot of vent space for every 1500 square feet.

Where to Place the Vents?

According to the IRC, you should install at least one vent within three feet of every corner of your crawl space. This proximity of vents creates a cross-flow of air that circulates within the entire crawl space.

How Do Automatic Crawl Space Vents Work?

So, when to have the vents open and when to close them? Some people would open them in the summer and close them during winter to prevent the cold.

To make life easier, you can install automatic vents that open and shut according to the temperature.

They close whenever the temperature drops below 40 degrees to prevent the pipes from freezing. Later, they reopen automatically when the temperature reaches 70 degrees or above to allow the circulation of fresh air.

What Are Ventilation Fans?

Otherwise known as circulation fans, these mechanical devices control the moisture content in your crawl space. These fans are effective when installed as part of a functional ventilation system.

The catch here is not to install ventilation fans haphazardly. In other words, if your crawl space relies on natural ventilation, there’s no need to change the mechanism.

How to Overcome Crawl Space Issues?

You may face several problems in your crawl space. We recommend addressing them holistically. Here’s what you need to do:

• Start by solving any moisture problem in your crawl space. Pump all excess water out of the house.
• Encapsulate your crawl space by installing a vapor barrier on the walls and floor.
• To keep the level of humidity in check, use a humidifier. This device controls humidity levels all year long.

Final Thoughts

Does a crawl space need to be vented?

There’s a strong debate concerning this question. In the past, people generally advocated venting crawl spaces.

However, strong evidence has recently appeared to refute this idea. It turns out that vents aren’t the best option for several reasons.

Whether you install vents in your crawl space or not, you should abide by the rules set by the International Residential Code (IRC).

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