Encapsulating your crawlspace is definitely the way to go for a more energy efficient, comfortable and healthy home.
Even though a vented crawlspace is an acceptable method of construction in the eyes of the building code, it is becoming more evident that it is not the best method.Having the open vents just allows the unconditioned air into the crawlspace along with the moisture it brings with it. Most crawlspaces that I see are open to the basement allowing that unconditioned air and moisture into the home.
The best way to treat your crawlspace is the same as your basement. You want to insulate around the perimeter and provide some conditioned air to help control moisture further. This will keep the crawlspace much warmer, dryer and will reduce the potential of pipes freezing if there are any.
Another downfall to the code acceptable method of vented crawlspace construction is the location of the insulation.
- Insulation is hung in the floor joists to block the heat transfer which actually make the crawlspace cooler.
- Plus the insulation is always fighting gravity and over time the paper facing absorbs the moisture causing the paper to rip and fall.
There has been some great research done by the Building Science Corporation (here) and another great article at GreenBuildingAdvisor.com (here) that should ease your mind that sealing the crawlspace is the best thing for your home.
For more information:
Read Dietmar Lorenz's Q&A "I need to add insulation beneath my wooden floor. What materials or systems do you recommend?"
Also, check ourbasement moistureQ&A to see what other homeowners and contractors are saying about vapor barriers, insulating foundation walls, etc.