Are Open Crawl Space Vents Bad?

Crawl space vents are fairly common in Northeast NC and were installed in homes that were built between 1950 and 1990 as a matter of best practice. This was done because industry specialists believed that crawl space ventilation would prevent dampness and humidity in a property by increasing airflow. Of course, later studies found that such vents do in fact increase airflow. Unfortunately, it is not a good thing.

The increased airflow has two main effects on a home. Firstly, it contributes to something called the stack effect. The stack effect, also called the chimney effect, is a process by which a channel of air runs from the bottom of a property to the top. This can cause issues in any home, and will be most pronounced in mid-summer and winter when your HVAC system is in full use. The stack effect is fueled by how air reacts to being heated or cooled. Since artificially-processed air rises or sinks, it will exit your home and draw in air from outside.

This causes a number of issues, the foremost being high relative humidity. The summers in Northeast NC can be muggy and humid, anyway, so keeping a property’s interior relatively arid can be a challenge. In a home that has exposed crawl space vents, it is almost impossible. Dampness, of course, has a number of negative side effects, including the increased risk of wood rot and mold formation. So, all in all, it is best to cover your vents where possible.