In today's economy, many people have become energy conscious. In order to save on those monthly energy bills, homeowners have come up with some creative ways to seal off their homes from the elements. Unfortunately, some of the common methods being employed are actually detrimental to the health of the home, and do little to accomplish the desired end. One of those methods is closing off or covering the crawlspace vents in the curtain wall.
It seems to make sense. Here in the south, insulation is rarely installed under the floor of a home with a conventional foundation. Our warm climate does not dictate the necessity. But in the winter, the idea of cold air circulating under your house makes you shiver, and that first winter energy bill makes you shudder! So, you reasonably figure that closing off those "pneumonia holes" all around the house will keep some of the warm air in, and the cold air out. Right? WRONG!
Closing off crawlspace venting does little for your bottom line on heating or cooling bills, and may have serious repurcussions as well. The purpose of all those holes in the side of your home is to allow air flow. The purpose of having air flow in your crawlspace is to prevent the accumulation of water vapor. The purpose of preventing this accumulation, in turn, is to prevent actual structural damage, discourage the growth of molds which may be detrimental to your health (especially small children!), and to encourage wood destroying insects to look elsewhere to establish a colony.
"Oh, come on!" you say. Surely a little water vapor can't do all that!! After all, we live in a humid climate here in the South. Humidity is everywhere. Yes, that is true, but here is what happens: When you close off those vents, you trap whatever moisture is already in the air under your home. The humidity is increased every time it rains, especially if the drainage around your foundation is inadequate in areas. Eventually, the floor joists and girders, even the masonry piers under your home become saturated with moisture. Molds love the combination of wood and water. The damp, cool soil is an invitation to termites.
I have learned over time to put on my high-tech filter mask when entering a crawlspace that has been sealed off in such a manner. Why? Mold. Depending on how long venting has been compromised, I expect to find joists and girders that are damp or even wet to the touch, with molds and fungi visible on the surface. I don't want to breath in spores that can make me sick! In addition to that, joists can become bowed, weakening the home's strutural integrity. Think about this. When a craftsman want to curve a piece of wood, what does he do? If you've ever re-caned an old chair, what do you do with the caning material to make it pliable? That's right you soak it! That is exactly what happens when you trap water vapor under your home! The process is much slower than immersion, of course, but the end result is the same. You create weakened wood structural members that are slowly bowing and rotting. Your kids start to have respiratory problems, and you don't know why. Eventually, shoring up floors with extra piers and girders, or having to get rid of mold becomes an expensive proposition. Suddenly, a few (and I do mean a few) saved bucks on an energy bill looks like a bargain.
So get out there and yank off those neatly cut plywood planks you stuck over those holes four years ago! If you don't have it already, make sure there is a plastic vapor barrier covering the ground under your crawlspace. Check out your drainage around the foundation, and make sure that roof drainage and surface water is moving as quickly as possible away from your foundation. You can pat yourself on the back when you don't have to take out a second mortgage to fix a terrible mistake.
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