We're building a 3,500 sq. ft. home with stamped concrete front and back porches which extend the full length of the home. This means that we are only able to ventilate one side of the crawl space (which is approx. 4' tall). Before the roof was on we had a lot of water which made it to the crawl space which caused the area to become very moist (even though we laid a layer of plastic down before we covered it with base rock and 1" clean). Anyway, last night I noticed mold growth (about 2 sq. ft of active mold) on a piece of the floor joist. I'm considering adding vents into the garage (on the opposite side of the other vents) to increase air movement. I'm also considering hooking up an attic fan to a humidistat to move air even more effectively. Any reasons why I wouldn't want to add foundation vents into the garage area?

Something doesn't make sense. Why can't you vent the crawlspace to the outside the way it is supposed to be vented? It seems like the stamped concrete will be too close to the wood framing, and will therefore be a code violation.
If they are 8 inches down from the wood framing the way they are supposed to be, then there is room for vents.

In the south where mold is always a problem they have begun the process of basically making the crawlspace a sealed tomb which no moisture can penetrate.

First off however... you have a mold problem and it needs to be addressed right now. You must first control the moisture so either buy and install the largest dehumifier you can or rent a dessicant dehumidifier to completely remove the moisture from under there. Wood is an excellent feast for most molds and due to spore spread it will be all over if the moisture levels exceed 60 percent.

Second.... completely remove or pay to have the existing mold professionally removed. Make sure you where a mask if you do it yourself and a kevlar suit. You do not want a mold infection in your body... it *****... believe me.

Unless you plan on leaving the dehumidifier there (good idea since mold cannot grow where its dry.) you should hire or rent a spray pump and coat all wood surfaces under there with Fosters 40/20 or some other type of mold encapsulation agent.

If its humid there in the summer then vents will only make it humid there under your house... which will be bad. I would completely cover 110% all dirt surfaces with 6mil poly and a big overlap. Then remove all vents and spray the inside of the block so that no moisture can move through to the inside crawl.

I would leave a dehumidfier (with a pump) down there because the cost to run it (after it come on after shutting it down) is much less then a big mold problem. And make sure you can check it from time to time.

Last and not least... I would consider after insuring the space is completely dry... installing 2 inches of foam (sheets) to the bottom of the joists to completely isolate the wood from any possible moisture problems. And at the same time warm the entire floor of your structure.

Good Luck
Bill
ReddiWall@yahoo.com