5 Reasons Why Crawl Spaces Need Vents

Giovanni Valle is a licensed architect and LEED-accredited professional and is certified by the National Council of Architectural Registration Boards (NCARB). He is the author and managing editor of various digital publications, including BuilderSpace, Your Own Architect, and Interiors Place.

A crawl space is a narrow opening between a building’s first floor and the earth below. When it comes to your home’s structure and the people living inside, ventilating your crawl space is necessary and can have many benefits.

Here are 5 reasons why crawl spaces need vents:

Building codes in many cities require crawl space vents.
Crawl space vents improve the building’s air quality.
Having no crawl space vents can damage a building’s frame.
Vents prevent pipes from freezing in the winter.
Vents prevent moisture build-up and rot in the summer.

This article will discuss the reasons crawl spaces need vents.

1. Building Codes in Many Cities Require Crawl Space Vents

According to section R408.1 of the IRC (International Residential Code), all buildings must have a minimum of 1 square foot (0.09 sq. m) of ventilation for every 150 square feet (13.94 sq. m) of crawl space. This regulation is applicable unless your city or state has overridden it.

Some cities don’t require crawl spaces to be ventilated, while others (such as Washington state) have a variation of this regulation. In Washington state, crawl spaces should have 1 square foot (0.09 sq. m) of ventilation for every 300 square feet (27.87 sq. m) of crawl space.

The chances are that your local authority requires ventilated crawl space for all buildings. If you’re unsure whether they do, it’s worthwhile to check the laws to ensure that you are meeting legal requirements.

2. Crawl Space Vents Improve the Building’s Air Quality

Approximately 40% of a building’s air comes from the underlying crawl space.

Moisture can quickly build up in an unventilated crawl space during the summer, resulting in excess humidity. Over time, these conditions can result in mold, fungus, and mildew formation, intensifying as long as the crawl space is unventilated.

As the air warms up, the water vapor from the crawl space is drawn into your home through the vents. This is known as the stacking effect, and mold and mildew from the crawl space will eventually reach the air inside your home. They will then be breathed in by anyone inside the property.

The CDC (Centers for Disease Control and Prevention) states that mold and mildew can cause numerous health problems, including allergies, asthma, skin problems, and more.

Therefore, venting your crawl space can help prevent poor air quality and resulting health issues in your home.

3. Having No Crawl Space Vents Can Damage a Building’s Frame

A crawl space functions as protection for a building against the damaging effects of the earth below it.

Air can move freely in and out of the crawl space when properly ventilated, preventing moisture, mold, and mildew build-up.

Many homes and buildings have wooden frames and, since wood is a porous material, it’s prone to damage when humidity levels are high and may rot if left unchecked.

An unventilated crawl space will likely accumulate high levels of moisture during the summer (especially if your area experiences hot and humid summers). The resulting mold and mildew build-up affect the building’s air quality and the integrity of the building’s frame.

Over time, prolonged exposure to these conditions can cause the building’s wooden frame to rot, resulting in expensive and unnecessary repairs.

With the proper care, your home’s wooden structure can last for several decades. A ventilated crawl space forms part of a good wood maintenance plan as it promotes light and excellent airflow.

When continuously exposed to moisture, it can be almost impossible for wood to dry out. Wood with a moisture content of 20% or more attracts wood-boring insects, including Deathwatch Beetles, Wood Boring Weevils, and House Longhorn Beetles. Over time, these insects can slowly eat away at your building’s frame.

In addition, since the vents in a crawl space are slotted when open and contain screens, they can prevent animals (such as rodents, possums, skunks, and snakes) from making a home there.

Animals that live in a crawl space can tear up the building’s insulation, create holes in the foundation, and damage the floor above. They’ll also defecate and urinate in the crawl space, which can have a negative impact on your home’s air quality and smell.

Small animals can also bring ticks and fleas into the crawl space, causing a possible infestation in your home.

In addition, if an animal dies in your crawl space, it’ll attract bacteria as it decomposes. This creates a health hazard, as well as a terrible smell.

4. Vents Prevent Pipes From Freezing in the Winter

Ventilating your crawl space has the advantage of allowing you to decide when to open and close the vents.

When temperatures are below freezing point in the winter, the sewage and plumbing pipes in your home are susceptible to freezing. Most people don’t enjoy not having hot water, and an effective way to prevent this is by closing the vents in your crawl space.

Some homeowners take the extra step of plugging their crawl space vents with foam blocks if they don’t have automatic crawl space vents.

During the winter, the air is typically dry and cold. This means that it’s unlikely that moisture, mold, and mildew will accumulate. Thus, they will be unable to negatively affect your home’s air quality and damage the wooden frame.

5. Vents Prevent Moisture Build-Up and Rot in the Summer

During the summer, many areas experience heat and humidity, which can cause unwanted moisture, mold, fungus, and mildew build-up in the crawl space.

With a ventilated crawl space, vents can be left open during the warmer months to promote air circulation and keep the crawl space’s air dry and fresh.

If your crawl space has a dirt floor, you might want to lay down plastic sheeting to prevent moisture build-up further. This is also known as a vapor barrier, and it’s widely available at most DIY stores. If you don’t mind squeezing into your crawl space, you can install it yourself.

If you live in a very humid area, you could also consider including a dehumidifier in your ventilated crawl space for added peace of mind. It’s best to let a professional install a crawl space dehumidifier.