By Dana Hart
For the Salisbury Post
Certain times of the year, I get phone calls from homeowners about their wet crawl spaces. It seems that there is an expectation that a crawl space is supposed to be dry. Crawl spaces by their very nature are not dry spaces but quite to the contrary, wet. I’ll explain why shortly. A crawl space is the area between the dirt and the bottom of the floor surrounded by foundation walls. One would think that a crawl space would be common and ordinary by now. After all, how complicated and technical can a crawl space be? First, I think I need to dispel a few common misconceptions about building in general and crawl spaces in particular. Just because a house is built to the Building Code doesn’t mean that you will be satisfied with the finished product. And just because the Building Code approves a system and the builder installs it as designed does not guarantee it will perform to your satisfaction or expectations. That seems to be the case with a lot of crawl spaces.
Here are some things to consider when you think about crawl spaces. Think of a glass of ice tea sitting on the porch rail in the summer. Are there not beads of water on the outside of the glass? Did the water move through the glass or did water condense on the outside of the glass? Consider a roll of paper towels sitting on the kitchen counter. Will it not soak up a spill from the bottom until either the towel is saturated or the spill is gone? What happens in the crawl space when the temperature reaches the dew point?
As I think about these things it occurs to me that a crawl space is pretty complicated. It’s a mini weather system. Think about the TV weatherman or weatherwoman and all that stuff about high and low pressure areas and relative humidity. Well, all that happens in the crawl space right under your floor. It even rains down there. That’s what happens when the temperature reaches the dew point.
If it wasn’t so complicated and so prone to problems then there wouldn’t be all kinds of new crawl space technology on the horizon and in the Building Code. For example there are new systems now available for builders and home owners alike. There is the closed crawl space which eliminates all the foundation vents and there is the conditioned crawl space which not only eliminates the vents but supplies the crawl space with heat and air conditioning. Of course, all these systems have their drawbacks. The closed system and the conditioned system both have the potential to trap Radon and both have a tendency to hide a termite infestation, if not attract them with their use of foam plastic insulation. The old system has its drawbacks too like moisture infiltration, mold formation and somehow it’s the perfect habitat for crickets and spiders. So, there is no perfect system when you enclose the space under the floor. Water can wick up the foundation wall or rise from the dirt floor. Remember the ice tea glass and the roll of paper towels? Water can condense on cold surfaces and drip on the floor. Water will find its way into the crawl space.
A crawl space is like any system on a house. It requires the home owner perform periodic inspections and maintenance. If you’re not up to the task of dealing with water in a crawl space and you are looking for a new house, you might consider a house built on a slab. I’m not talking about a slab on grade or a slab at ground level. I’m talking about an elevated slab. Elevate the slab a minimum of 8 inches above the surrounding landscape, install a vapor barrier below the slab and perhaps an in-floor radiant heating system. Or what about a house with a basement? Basements are partially or completely below ground. Because of this feature they tend to be below the water table or subject to ground water infiltration. However, a basement is constructed differently than a crawl space and waterproofing requirements are more stringent for a basement than for a crawl space. The basement is more like a part of your house than a crawl space and tends not to have a different weather system than your house. It also receives more scrutiny during construction and less scrutiny after.
To sum it up, crawl spaces, by their nature are designed to be wet and basements are designed to be dry. Just something to consider.
Dana H. Hart
Director Rowan County Building Code Enforcement