crawl space - moisture problem

Ranch style home with crawl space in SC along coast that is five years old. This crawl space has 28% moisture readings in two or three areas of the joists. The crawl space has approx. 2,179 s.f. with. The design of house has two long earthen porches on the front and rear of house without any ducting to allow venting to the crawl space. The HVAC ducting is in attic, so this is not an issue. There are no plumbing leaks in the crawl space. As such the house has no crawl space vents on front, six on one end, four on opposite end and six on the rear of house. A building inspector when we purchased the property (three years ago) recognized this moisture problem and recommended vapor barrier (plastic on ground) and two power vents. Vapor barrier probably covers 75% of ground. I have installed a third power vent and moved the power vents to one end of the house, closed all the vents on the end with the power vent and opened all the vents on the opposite end of the house. I was having a problem with high moisture, mold build up on joists in the middle of the crawl space against the walls where the porches are, so I modified the power vents to pull air through the crawl space to avoid those "dead" areas along the porch walls. The power vents move approximately 33,000 c.f. of air per hour. The question is should I cover the remainder of the crawl space with 6 mil platic and have the plastic go all the way to the walls and up them for 6 to 12 inches to help alleviate the moisture problem? Any other suggestions on how to alleviate this moisture problem!
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The complete floor should be covered. It sounds like you may have poor drainage and water is getting in. You say the mold is near a wall. Use your moisture meter to locate the water when its raining, 28% moisture in wood is caused by water leaking not humidity. Fix your leaks and you wont need the fans,, Im sure you are spending 40 - 70 a month to run them.
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Yes, and overlap the new over the old. Don't go too light on the thickness either. The overlapped area should be taped with a GOOD tape, not the type you get at a hardware store, but that like #357 Nassau, that stuff will never come loose. Clean the plastic on the existing where the tape will be.
Run it up on the walls to secure it, or place clean stones in the corner of the floor and foundation to force the plastic to stable itself. I Have seen people tape or staple to the sill plate, DON"T DO IT, it may cause problem. Also, don't run it all the way up, you wont be able to inspect for termites and other problems. Maybe an adhesive that doesn't harm plastic can be used, I'm thinking of the company that makes Liquid Nails, they have lots of products for these kinds of project.
I once had a home so laden with moisture that the windows and doors were freezing shut in the winter time. Hot water heat, The homeowner did this very thing and we ended up putting a humidifier in the home because it was so dry after wards.
Rich
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Ferroj wrote:

The plastic covers 75 percent of the ground? That's like having a roof that covers 75 percent of the house. Until you get all of the crawl space covered with plastic, you are wasting your time. Yes, cover with plasitic upto the walls and at least 1 foot up if the walls are concrete. Otherwise it you seem to have a good handle on what to do. Good luck.
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See www.eren.doe.gov (Dept of Energy) and search for Technology Fact Sheet titled Crawlspace Insulation. May identify it as number DOE/G010099-774. This covers the subject in great detail.
Ferroj wrote:

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