Question: I have a crawl space under my home instead of a full basement. It has a dirt floor and I have noticed it smells and seems damp. I have been told different things. That it needs more ventilation and I have been told to seal off the ventilation and add a vapor barrier to cover the dirt. What do I do?

Answer: Crawl spaces are cool because the dirt is 55 degrees year-round. So when we bring in humid air into a crawl space, the air is cooled, and the humidity goes up. High humidity causes rot, mold, energy loss and attracts pests.

So here's the problem — many years ago when the building codes were written, they thought since we have a large amount of moisture from the ground in the dirt crawl spaces that something had to be done about it. It was figured that if the crawl space was vented, the moisture would travel out the vents, solving the problem of moisture damage.

Many things were not taken into consideration. When it rains, the vents would be taking in damp air. When it is cold, they are taking in cold air. When it is a hot day, the vents would be ventilating with hot air, and when that mixes with the cold dirt floor, you could have as much as 99 percent humidity in the air in the crawl space. It also was not considered the air would flow upwards into the house.

I have inspected many crawl spaces and you would not believe the amount of moisture and rot found on the joists and sill plates because of moisture penetration into the crawl space.

Bugs love damp crawl spaces. I sometimes take a broom with me in a crawl space so I can get past the thickness of numerous spider webs. Mice and rats love the damp area. It's hard sometimes to inspect because of all the debris.

There are four steps to help eliminate the negative effects of the crawl space on the rest of the house.

Step 1 — Fix the water leakage if there is any.

Step 2 — Isolate the house from the dirt. I have seen people use 6 mil plastic to cover the dirt. There is a company that specializes in crawl spaces that installs a solid heavy membrane that encompasses the entire crawl space. It is a fabulous product and company. If you are interested, email or call and I can give you the contact information.

Step 3 — Seal the vents and any other outside air leaks.

Step four — If possible, condition or dehumidify the air. In some newer homes, the crawl spaces have a concrete floor and no air vents and they are nice and clean and dry.

Remember, keeping water away from the foundation with proper landscaping and gutter and downspouts with long extension can be a big help. (Some of the information for this article was taken from a book called crawl space science by Lawrence Janesky.)


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