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How To Properly Ventilate Your Crawl Space

Sam Smith Foundation Repair Consultant

Ventilation is necessary to maintain a healthy crawl space air quality

Looking for accurate cost information related to crawl space ventilation?

Perfect, you’re in the right spot. In this guide, you’ll learn:

  • How does crawl space ventilation work?
  • Why should crawl spaces be ventilated?
  • What are some downsides to crawl space venting?
  • Can you ventilate your crawl space yourself?
  • How can you save money on crawl space ventilation?

Crawl spaces are often damp, musty areas of a house that many homeowners neglect. They can easily trap moisture in the air from the surrounding soil, creating numerous problems in the under-home area and the living space above.

Crawl space ventilation is a bit of a heated topic regarding how ventilation is most adequately done. Regardless of the method, ventilation of some kind is necessary to maintain a healthy crawl space air quality, regulate the temperature and humidity in your upper floors, and prevent property and water damage.

Below, I’m going to go over how crawl space ventilation works, why the area under your home needs to be ventilated, and the pros and cons of adequate ventilation. We’ll also offer some tips on how to save money when installing crawl space ventilation.

How Does Crawl Space Ventilation Work?

Crawl space ventilation is similar in theory to the ventilation of any otherwise enclosed space. The idea behind ventilating the area under your home is to help prevent mold growth and mildew formation and to limit the buildup of crawl space moisture.

There are two primary forms of crawl space ventilation: open ventilation and closed ventilation.

Open ventilation provides airflow into and out of the area through openings in the crawl space walls. Open vents are covered with a metal mesh to prevent liquid water, rodents, and other pests from getting into your home.

Closed ventilation systems – also called unvented crawl spaces – are now allowed according to the international residential code (IRC).

These systems require full crawl space encapsulation. Once an airtight seal is created around the crawl space floor, walls, ceiling, and any openings in your crawl space walls with a vapor barrier, ventilation is provided in one of three ways.

a crawl space with air mover to dry out the structure

Homeowners can choose to move some conditioned air in from the living space above via their ductwork, move stagnant air out through an exhaust fan, or couple an air intake system with a dehumidifier and sump pump to remove moisture from the air.

Closed ventilation systems are referred to as “unvented crawl spaces” even though there is some form of ventilation at work.

Unvented crawl spaces have the added benefit of being able to stop radon from entering your living space, as the vapor retarder often acts as a radon barrier as well.

Why Should You Ventilate Your Crawl Space?

Foundation Repair Cost In San Antonio-3

Crawl space ventilation is essential because it helps manage the relative humidity and temperature of the area under your home.

Moisture buildup in your crawl space is detrimental because it can wood rot on beams, floor joists, and other construction material. It can even warp the flooring or the wall studs of your home’s first-floor area if it is severe enough.


Moisture also leads to the growth of mold spores and mildew formation and attracts termites and other insects. Proper ventilation can lead to drier, safer air in your crawl space.

Humid air in your crawl space can seep up into your living space as well in a process called the stack effect. It can make your home hotter in the summer and colder in the winter, making your home less comfortable and increasing your energy bills.

Compensating with your heating system or air conditioning can put undue stress on your equipment and lead to failure and necessitate repairs.

Adequately ventilating your crawl space will make your home more comfortable, can offer advanced energy efficiency, and can help prevent problems with your HVAC system.

Are There Any Problems With Ventilating Your Crawl Space?

There are some issues with both open and closed ventilation systems.

Open vents are more likely to allow liquid water in, which can contribute to problems with moisture control. They also don’t allow you to regulate your crawl space temperature effectively, given that they are open to the outside air.

As such, crawl spaces with open ventilation can still lead to a slightly colder home in the winter and a warmer home in the summer.

Closed or encapsulated crawl spaces still require some forced ventilation and humidity control via air pumps or dehumidifiers, and these systems can be costly to install and maintain.

Closed ventilation is not suitable for areas with high water tables or where liquid water getting into your crawl space is a common problem.

Crawl Space Ventilation vs. Unvented Crawl Spaces

Vented crawl spaces with open vents aren’t temperature controlled, so there is more of a chance of heat loss from your living space to the area under your home.

Open vents are suitable for areas prone to flooding, but they are also more likely to let in small amounts of rainwater and moisture from the surrounding soil. They are generally more prone to interior moisture problems and mold growth.

Unvented crawl spaces that are encapsulated and vented via an air pump or conditioned with indoor air or a dehumidifier are better at resisting moisture buildup under your home.

They are better for regulating indoor air quality and temperature, and they rarely have mold or mildew issues. However, they’re far more expensive to install and more costly in ongoing maintenance.

Can You DIY Crawl Space Ventilation?

Many homeowners wonder if there are DIY solutions for crawl space ventilation to save on labor costs, especially because the job doesn’t need to be cosmetically perfect.

If your crawl space has open vents installed already, removing and replacing them is a simple DIY project if you’re looking to keep an open ventilation system.

You would simply need to purchase new vents of the appropriate thickness and replace the current vents in your foundation walls. Most crawl space vents have standard dimensions, but make sure you get the same size vent to fit your current wall openings.

Crawl Space Freezing Pipes

If you’re looking to seal your currently open crawl space, we strongly recommend having a professional do the work for you.

Crawl space encapsulation needs to be done correctly to get a good seal from the outside moisture and temperature conditions. There are numerous ways to install an encapsulation improperly that can lead to failed seals, additional moisture problems, and the eventual professional fix.

Additionally, the air in a sealed system must be treated with outdoor air, indoor air, or a dehumidifier. Installing air pumps or dehumidifiers can be tricky and potentially dangerous, so I recommend letting a professional do this work as well.

This is why we highly recommend reaching out to one of our professionals to evaluate your unique situation and help you resolve it properly.

How To Save Money On Crawl Space Ventilation?

The average cost of encapsulating and installing a dehumidifier is around $7,500 per 1,000 square feet of crawl space, so many homeowners look for ways to save money during the process.

The best way to save money is to have a closed ventilation system installed if the building code in your area permits it.

Closed ventilation systems are generally considered superior to open ventilation because they improve the temperature and humidity in your living space, decrease the associated strain on your HVAC equipment, and lower your energy bills more than an open system.

If your crawl space already has open foundation vents and you’re looking to replace them, you can save money by replacing them yourself and saving on the labor costs that come along with hiring a professional. Just ensure that the vents you purchase are the same size as the old ones to prevent having to cut new openings in your foundation wall.

Conversely, you can save money on installing closed crawl space ventilation by having a professional do the work for you. Installing a vapor-barrier material is challenging and must be done correctly to get a good seal. Setting up equipment to control the air quality in your newly enclosed crawl space can also be challenging.

There are numerous errors inexperienced homeowners can make when attempting to install a closed ventilation system themselves.

You’ll pay more for professional installation, but you’re less likely to have problems with the system that will require future costly repairs.

We recommend paying a professional to do it the first time around and avoiding potential property damage from an ineffective DIY solution.

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Sam Smith Foundation Repair Consultant
SHORT BIO: Hey, I'm Sam Smith. I'm one of our service techs here at Regional Foundation Repair. I'm here to help you learn more about your home's foundation. I've been doing this for a while, so I have a few insider tips and tricks to share!

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