Why Do Crawl Spaces Have Vents?

Having a crawl space vent brings about many problems in a home, so why are crawl spaces built with them? Many years ago, crawl spaces were built with vents because it was believed they would prevent humidity problems.  

• Misconceptions 

When a room has a nasty smell or when it’s incredibly humid, what does one usually do? Airing out a room is a great way to get rid of smells and humidity, which is why rooms have vents; to make sure the air doesn’t become stagnant and harmful to breathe in. This is why crawl spaces have vents—because it was believed that crawl spaces wouldn’t become humid as long as they had ventilation. 

However, ventilation doesn’t work well in a crawl space. First, a crawl space is too small and enclosed for the humidity to be aired out properly. Second, wood, concrete, soil, and any fiberglass insulation will hold moisture. In a bedroom, if the mattress is completely wet, it doesn’t matter if the window is open, the bedroom’s humidity levels will be higher than the rest of the house because of the amount of moisture the mattress contains. The same thing happens with crawl spaces due to the materials inside that hold a lot of water.  

• Local Building Codes 

More and more homeowners are realizing that having open crawl space vents is actually detrimental to the structural integrity of their home. Unfortunately, when most of the local building codes were re-written, the idea that airing out a crawl space was still widely accepted. Despite there being research proving enclosed crawl spaces improve living conditions, building codes have yet to be updated in many parts of the country. 

Because of this, even newly built homes need to have vents in their crawl spaces. Modern houses can be built with enclosed crawl spaces, but due to building codes, there are a lot of hoops to jump through if this is to be done. Most site managers don’t consider the trouble to be worth it, so crawl spaces with open vents are still built regularly.