How to Vent a Crawl Space (An In-Depth Guide)

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Are you worried that there’s too much moisture in your crawl space that it might attract mold? If so, you’re probably wondering how to vent it.

Venting a crawl space is a three-step process. First, the vent space area needs to be calculated. Then, homeowners should decide on a vent type to use that complies with IRC regulations. The final step is to decide on the optimal ventilation method to adopt.

Read on to learn more about what you need to consider when venting your crawl space. We’ve also outlined why doing so may not be the best idea.

Why Do You Need to Vent Your Crawl Space?

Venting your crawl space is crucial because excessively humid conditions can lead to the floor joists holding it up getting damaged.

The humidity encourages mold to develop on the wood. This causes it to rot, and may ultimately lead it to break, and broken floor joists don’t bode well for your home’s structural integrity!

Venting your crawl space allows you to eliminate moisture, which, in turn, helps you avoid all of the above-mentioned problems.

Venting Your Crawl Space: Considerations and Requirements

There are a lot of factors to consider when venting your crawl space.

First off, you need to know how big an area requires ventilation. Once you’ve figured that out, your next step is to settle on a type of vents to use.

Finally, you want to make the right choice when deciding which ventilation method to go for.

Here’s an outline of these steps in more detail:

Calculating the Area You Need to Vent

As we’ve all learned in school, you can calculate the area of a rectangular space by multiplying its length and width.

You can use this formula to determine the total area of your crawl space. This is only the first step in calculating the actual ventilation area required, though.

Next, you need to divide your crawl space’s total area by 150 to determine the vent space area. Once you’ve done so, proceed to divide the vent space area by two to calculate the soffit vent area.

The final step is to multiply the soffit vent area by 144. This converts it to inches, which is in line with the vent specifications most manufacturers use.

Here’s a quick example of these calculations for a crawl space with dimensions of 30 by 40 feet:

1. Crawl space area = 30 x 40 = 1200 square feet
2. Vent space area = 1200 / 150 = 8 square feet
3. Soffit vent area = 8 / 2 = 4 square feet
4. Manufacturer specifications = 4 x 144 = 488 square inches

So, you would need 244 inches of exhaust vent area and 244 inches of intake vent area for a crawl space of the aforementioned dimensions.

Determine the Vent Type You’re Going to Use

Your choice of vent type to use for your crawl space is governed by International Residential Code (IRC). This is the authority that sets the rules for building requirements for one and two-family dwellings that are up to three stories tall.

Here are some of the vent types allowed by the IRC:

• Cast-iron grating
• Hardware cloth (0.035+ inch wire)
• Expanded metal sheet plates (0.047+ inch thickness)
• Corrosion-resistant wire mesh (0.125+ inch thickness)

IRC regulations also dictate that each vent needs to have a minimum area of one square foot.

Choose Your Ventilation Method

Have you figured out the vent space area you’ll need and the type of vents you’ll use?

Now it’s time to settle on a ventilation method to go with.

Here are some of your options:

Release Crawl Space Air to Outside

Using an exhaust fan to release air to the outside is the simplest crawl space ventilation method.

It allows you to free your crawl space from the humid air and moisture that can lead to mold and other complications.

Make sure to place the fan in a suitable spot to get the best results.

Intake Outside Air

You can also get the air flowing through your crawl space by using intake vents to bring in fresh air from the outside.

However, be noted that this method isn’t advised if you live in an area with high humidity. This is because the humid outside air will do more harm than good to your crawl space.

Hook Up Your Crawl Space to the HVAC System

Instead of exposing your crawl space to the outdoors (either to intake or exhaust air), you can alternatively use your HVAC system for ventilation.

Conditioned air from your HVAC system is quite dry. This is optimum for maintaining a low humidity level in your crawl space.

If you already have an HVAC system installed, we highly recommend this method.

How High Should Crawl Space Vents Be?

The recommended height for your crawl space vents depends on one main factor: the height and spacing of the floor joists holding your crawl space above the house’s foundation.

However, the typical crawl space vent should be around 11 inches above the ground.

How Do Crawl Space Vents Work?

There are two types of crawl space vents: manual and automatic.

Manual crawl space vents require you to open and close them yourself. When you should do so depends on the temperature outside. When it’s less than 40℉, you should close your crawl space vents.

However, you should make sure not to have the vents closed more than necessary. Failing to do so can have a reverse effect and make your crawl space more humid.

On the other hand, automatic crawl space vents have built-in sensors that allow them to open and close themselves as the temperature goes above and below the aforementioned threshold.

This is pretty convenient, but there’s a catch! Automatic crawl space vents have been known to be unreliable and not durable. Therefore, we recommend that you keep a close eye on them to avoid moisture build-up in your crawl space.

Is Venting Your Crawl Space a Good Idea?

Although venting your crawl space does have its benefits, it also has some downsides.

This is especially true for homeowners living in humid areas. Exposing their crawl space to the outside via vents can actually lead to a higher humidity level in there.

Another issue with venting crawl spaces is that it opens them up for pests such as termites. Once such pests grab a hold of your crawl space, there’s very little you can do to combat this. They’ll start chewing through the wooden structures and wreak havoc on your home.

Finally, you don’t have much control over the quality of air entering your crawl space through vents. In turn, these vents can bring harmful gases that can damage your health and that of your family members.

Final Thoughts

To summarize how to vent a crawl space, the first thing you need to consider is the size of the crawl space area to be vented.

Next, you’ll need to decide which type of vents you want to use. Finally, you’ll need to decide whether you want to let air into your crawl space or expel it.

Use the tips in this guide to keep your crawl space in tip-top shape for years to come!

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