Unless required by Code: “Crawlspaces should be designed and constructed as mini-basements. Crawlspaces should not be vented to the exterior (see FAQ on Crawlspace Venting). They should have their floors uninsulated, the ground vapor sealed, their walls insulated and air sealed, and their air conditioned with indoor air.
Crawlspaces should have a continuous sealed groundcover of vapor diffusion resistant materials, such as taped polyethylene or, preferably, a thin poured concrete slab over polyethylene with perimeter and control joints sealed.” From: http://www.buildingscience.com/docum...d%20in%20walls
If vented, vapor retarder faces the conditioned living space above, never a vapor barrier.
Clothes taking longer to dry?
Clean the dryer screen in HOT water if using fabric softener sheets.
They leave a residue that impedes air-flow, costing you money.
Clean the ducting in the last six months? 17,000 dryer fires annually!