You can check out the building science website (www.buildingscience.com) and visit the thermal control portion of the website. If I recall correctly, do a search for 'conditioned crawlspace' and there are a number of different papers which detail this topic. Specifically, look for anything authored by Joseph Lstiburek.

Dixie, DH and I were just recently researching crawl spaces and what we should do with ours. All the sites I came across that had the ventless crawlspaces, had the plastic on the floor bed and up the sides. I do not remember any with any insulation up against the joist. Of course the problem with putting insulation up to the joist is having to worry about moisture if you live in an area with very high humidity. Even though they say it is sealed all around, all it takes is one hole to let in moisture. We've opted to vent the crawl space which will be bricked on all sides and put insulation board on the inside of the bricks and also attach to the joists. That way if any moisture does get in, it will air out. We will have the automatic venting and hopefully it will work properly. I don't know if this information will help with your application, but just wanted to mention it.

Dixie - We built an enclosed crawlspace as it is better for our humid climate (we're in SC) in terms of mold growth and energy savings. Since we had to elevate 4 ft for flood reasons, we still had to have flood vents. We were able to use "SmartVents" which are insulated for a closed crawlspace and balanced so they will open to the pressure of rising water. They are pricey though!

The crawlspace walls are insulated with foam and the floor covered with heavy plastic - 8 ml I believe, it's been a while since we installed it. We are using passive venting with a 'through vent' in our pantry which has its own returns. We did it ourselves as we are our builders :) You can hire a company to do it for you or your builder can do it fairly easily with some directions. Duke University did a very good study on the benefits of enclosed crawlspaces with directions and diagrams on best built practices.
This site has some very good information and helpful diagrams *warning some of the files are quite large. Downloading on dial up can take a looong time  ask me how I know :)

Here is a link that might be useful: ventless crawlspace info

Thank you all for the information. I will take a look at the links that you all have provided. As background, we are having a ventless conditioned crawl space in our new home. Our builder has already added the (DOW)Styrofoam insulation to the walls, I know that he will eventually seal the bottom with a heavy mil plastic (I think that he had mentioned that it was heavier than 8 mil...I thought that he mentioned a 16 mil covering...chiroptera_mama, are you sure that yours is 8?), but I wasn't sure if we were also going to have insulation in the floor joists.

Does the above link address the passive venting that you have? I'm not sure that I know what the purpose of a 'through vent' is....or, really even what a through vent is!
Thanks again.

On the buildingscience.com site you can order builder's guide books..maybe even look at them online. Check the info out for your climate.
I recently saw the Smartvents @ LaHouse in Baton Rouge.
Lstiburek consulted with several other building specialists on this project.

Check the link. (pdf file) Lots of photos!

Here is a link that might be useful: Closed Crawl Spaces Do Double Duty

Let's try that again.

(For pics, open PDF file from the site.)

Here is a link that might be useful: Crawl Spaces do Double Duty

We built a sealed crawl space in our home. It is insulated on the side walls and is conditioned with a vent into the crawlspace. As well, we have 20 mil plastic along the ground, joined at all seams, and joined to the walls with mastic. We also have a dehumidifier there which we have a switch for in the house to turn on in the summer.
This past hot summer, the temperature never went more than two degrees above our house temperature. The relative humidity never went above 50%. In other words, the air quality of the crawl space was as good as the air quality of the house. My understanding is that there is no need for insulation on the floor since the crawl space is a conditioned area and since the building envelope includes the crawlspace.
In the hottest month this summer, our electric bill for AC was 100 for a 5000 sq foot house. The crawl space definitely contributed to the efficiency and to the comfort of the home.

Dixie  donÂt know how far down South in Dixie youÂre located, but IÂm right outside of New Orleans. I was planning to build with an insulated crawl space, but learned that LSU Ag Center does not recommend this for Louisiana. Here is a quote from their "Building Your Louisiana House" publication:

"However, such unvented, insulated wall crawl spaces
are not appropriate in flood hazard and high water
table areas. Also, insulation in ground contact is not
recommended in Louisiana because it provides a
hidden path for termites and other structural pests.
Likewise, insulation inside a crawl space is vulnerable
and difficult to inspect. Although termite barriers,
inspection points and termite-resistant insulation
treatments are strategies to overcome that problem,
there is not enough verification to balance the high
termite damage risk in this state."

Thank you all for the links. We are not actually evaluating the pros/cons of installing a ventless crawlspace. We have already made the decision that we are having one...I was just interested in learning more about the steps involved in finishing it off. We are not as far South as Louisiana (Central VA), and we aren't in a flood zone, so hopefully we won't have any of the issues above!!
Thanks again.