Crawl Space Ventilation and Eliminating A Musty Basement Smell

Years ago, especially in the southern US, houses were built on posts, or piers in order to avoid water damage. There was no need for crawl space ventilation, because there was a free flow of air to dissipate the humidity.

This worked well, until heating and cooling costs became a serious matter to contend with. By sealing the air space under the house with skirting, a crawl space was created. This helped to reduce heating and cooling costs, but brought a new problem: humidity and a musty basement smell to the area.

The building codes were modified to require vents in the crawl space, as this seemed a logical idea. As it turns out, the vents actually increased the humidity levels, especially during the hot, humid summer days.

Many experiments were conducted to determine whether or not it was a good idea to ventilate the crawl space. The conclusion was that most of the moisture under the house came from the ground up, and the best solution was to lay a polyethylene barrier sheet on the ground, and up the outside wall to the flooring.

Care must be taken to do this correctly, due to the fact that termites would be able to build nests along the plastic sheet and thus enter the house. Local codes and building guidelines certainly prevail in any given area. It pays to seek sound advice that relates to your own circumstances.

Depends on where you live

If you live in the eastern US, you should definitely seal the crawl space from outside air, especially if the house has air conditioning.

In the arid west, California, for example, building codes are quite different. The lack of ground and air humidity make crawl space ventilation a completely different matter. Vents are often quite helpful to dissipate whatever humidity has built up under the house.

As a boy growing up in dry Colorado, I remember our swamp cooler. It was really just a box of water with a fan to blow the cool water mist into the house. Can you imagine doing that in Mississippi?! This illustrates how different the requirements are from region to region.

If you do use vents under the house, make sure that they have wire cloth over them to prevent mice and other little varmints from moving in and causing problems.

One old farmhouse I lived in had a stone foundation and crawl space. When the pipes froze during our first winter there, I had to go down and wrap electrical heat tape and insulation around the pipes. I was shocked at how many bones were down there! Snake, rat, mouse and even some bird skeletons were lying around.

There was also evidence of water damage to the floor, due to the dampness under the house. Some of the wood was punky and needed to be replaced. I also needed to repair the foundation cracks that allowed the humidity and animals in.

The musty basement smell associated with a typical crawl space can be eliminated by removing the habitat for the mold and mildew that cause the odor in the first place. The polyethylene vapor barrier is usually the best place to begin. This is the first step in getting rid of mildew in a crawl space.

If you do need ventilation in your crawl space, here are some popular products on the market:

Atmox Crawlspace Ventilation Systems are designed to control the moisture levels in your crawl space. You can buy their system and install it yourself, or hire somebody to do it.

The Tjernlund UnderAire™ Crawl Space Ventilator — Economy One-Fan, 110 CFM, Model# V1 sells for around $70 and is quite popular.

The UnderAire Deluxe One Fan Crawl Space Ventilator is also a good buy. They go for around $100.