Ventilating vs Sealing a Crawl Space

The crawl space is a deceptively important section of your house. The fact that it can be damp and unsightly leads a lot of people to avoid crawl space maintenance until it becomes a major issue. However, the crawl space affects the quality of life inside your home every day. There doesn’t need to be a major issue in order for your crawl space to impact your life.

Here’s a quick snapshot of why you should pay attention to the conditions down there: 40% of the air inside your home comes directly from your crawl space. So if your crawl space is musty, dirty, and contaminated with mold — so is your home.

One of the major debates in the world of crawl spaces these days is how to make use of the vents. The traditional line of thinking is – the vents should be open in the summer and closed in the winter. But there’s a newer approach that says the vents should be sealed shut at all times.

But which approach is right for your home? Ventilating Your Crawl Space OR Sealing Your Crawl Space? 

Let’s explore the pros and cons of both.

Pros and Cons for Ventilating Your Crawl Space:

You will see your crawl space vents along the outside of your home. The size of your home will dictate how many of these vents exist. They look like thin windows along the ground that you most likely won’t be able to see through. Perhaps they are surrounded by wells to avoid water flowing directly into them.

The vents are meant to ventilate the crawl space in order to prevent mold growth. A vent on one side allows a breeze to enter your crawl space and carry the stagnant air out through another open vent on the opposite side.

This became the go-to method of ventilating a crawl space around the 1950’s.


Many building codes call for ventilating the crawl space. All modifications to a home should be verified with local codes to ensure the home remains in alignment with local stipulations.

Ventilated crawl spaces are generally less expensive. This is especially true since many homes were constructed back when ventilating a crawl space was the norm, so there are zero modifications that need to be made if a home is purchased.


Areas such as Nashville, Savannah, Huntsville, and other southern cities are generally humid. This means the air that is supposed to clear out the crawl space in an open vent system is just as humid as the air it is supposed to be replacing. The inability to regulate this humidity creates moisture and can lead to mold growth in the crawl space.

The “stack effect” draws the air from your crawl space into your home. Think of the hot air escaping through your attic as pulling the air pressure in your home upward. This pulls the air from your crawl space through your floorboards and into your living space. If the air in your crawl space is humid and moldy, the air quality in your home will suffer.

Pros and Cons for Sealing Your Crawl Space:

Building codes are catching up to the new methods of sealing up the vents underneath a home. Benefits are being studied and recommendations are slowly changing to reflect this.

The first step to a closed system is dealing with any standing water issues. Crawl spaces are occasionally dug below the water line and are apt to flooding when heavy rains hit. Proper drainage is essential to eliminating this moisture.

Vapor seals are to be placed along the ground, around support beams, and along the walls. Insulation is then placed along the walls to keep out the elements.

Properly designing a closed system will vary depending on climate and design of the home.


Air quality drastically improves inside the home once the crawl space vents are sealed. We’ve discussed how air from the crawl space gets into the home and what can be brought along with it when that air is substandard.

Along with insulation, a sealed crawl space can give the homeowner around 18% in savings for heating and cooling costs.

The possibility of structural damage to the home is reduced as the risk of mold growth is reduced. This improves the longevity of the house and maintains the quality of wooden surfaces.

The floor is noticeably warmer in the winter when the crawl space is properly insulated.


Since many homes have had open crawl space systems for a long time, a conversion process will be necessary. This can be fairly expensive.

These systems will require basic crawl space maintenance to ensure everything is sealed and working as it should. Crawl space maintenance might be easier to ignore with an open system, but it is always a good idea to keep an eye on your crawl space.

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