I've seen lots of discussion and comments on crawl space encapsulation. I was tempted to bite and called a contractor out to give me a quote. It was higher than I thought ($9k) for a 27'x27' and a separate 22'x22' crawl (both 3' in height).

The quote included "cleanspace" vapor barrier on the floor and up the walls/columns, and 2" "silverglo" insulation on the exterior walls. What was problematic for me was he said we could just leave the existing fiberglass in the floor joists and he did not at all address the rim joists. Should I walk away, or run like hell. If I were to do this, could I just pull the fiberglass myself and do rim-joists with board and can foam.

I am in southern Maryland (20736). Do i need additional insulation on the dirt floor and what should my goal be for R-value on block crawl space walls.

The house that I am in includes a conditioned crawl space, and it works well for my situation. However, it is unclear why you want to convert your crawlspace from an open to a closed crawl space. For new construction, I like the idea of a conditioned (closed) crawl space with the HVAC in the crawl, but what problem are you going to solve by converting to a conditioned crawl space? You already have insulation under your floor. Do you have ducts or heating pipes in the crawl space?

If you want to convert it to a closed crawl space, I would just leave the floor insulation in place. I would seal and insulate the rim joists with about 1" of spray foam and then cut up some rigid foam board to add on top of that and seal the rigid foam with more spray foam. The 2" of Silverglo or other rigid foam on the inside of the exterior walls sounds good if you leave the floor insulation in place. I don't see a need or practical way to insulate the floor, but you need a vapor barrier there. In this area they use a plastic film that is similar to those tear-proof mailing envelopes. I think that it is at least 10-mil thick. It needs go up the walls a couple of feet and be sealed to the walls. It would be nice to have some small amount of air flow into the sealed crawl space by using a continuously running exhaust fan (with ECM motor) in the crawl space to the outside, maybe 80 cfm or so.

Others on the forum may have some better ideas and more experience.

The crawl space is on engineered trusses similar to these:
http://trusssystemshawaii.com/wp-content/uploads/2010/03/maui-floor-trusses.jpg
The space is about 14" from bottom of floor to bottom of truss. The insulation is installed so it rests at the bottom of the truss, so there is a big 8" air gap above the insulation which allows free communication of air across the floor. It is impossible to keep the insulation up in place an invariably there is a spot that has fallen, so might as well be open to the outside.
The insulation does get moist which is why I wanted to seal the crawl space.

Finally finished, or mostly finished, mine in october. You floors will be much warmer. You will also have less mold odor in the summer. This smell went away in my crawl when I added plastic which I later took down from the rim joist and ramsetted it to the wall. I then insulated the wall with spray foam. I think with the spray foam the whole project might have cost $800-$1000. I also found that the old insulation was a haven for our flying squirrels in the summer as the attic was in the winter. No more mold or strange smells on the first floor. Also, we have had an unusually cold winter so far and while my coworkers are suffering from frozen pipes I dont have that issue because all of our pipes are under the house. The ductwork is also there along with an air handler. It just makes more sense.

A coworker looked at getting his crawl professionally done and they quoted him somewhere in the area of $3000 for a crawl on a 1200sft house. I think I convinced him that the foam at $600 for a kit would do the same thing but better and cheaper.