Insulating the outside is not that feasable. The foam board used for ground contact is R-5 per inch. To get any insulating value would require 2-3"'s. Plus you have to flash it at the top, bury the bottom edge into the ground and coat it with a special stucco material to keep it from self destructing from UV exposure. You do not remove rim joists on a whim. They are removed and replaced when the have rot issues. Removing a rim jost requires jacking the house up. No easy task,and no fun. This is the voice of experience. You have 2 solutions to insulate, get in the crawlspace and lay down a 6 mil vapor barrier and use fiberglass, or hire someone to spray closed cell foam in between the floor joists and on the interior side of the exterior walls of the crawlspace. Expensive,effective and waterproof.

R value is cumulative and does not depend on distance from the heat source. Foams have some of the highest R-values per inch available, and cost like it. If correctly done his proposal makes sense. You need a very good seal at the outside of the foam to prevent moisture entry since it will act as a second vapor barrier. Luckily most of the vapor in a crawl space comes from the earth and not the interior. Air infiltration casuses a lot more heat loss than less than adequate insulation.

yeah...Entergy is going to help you out! LOL! they do actually have a program in N.O. through Entergy using local energy raters. a little biased, but it is what it is. below is a copy & paste link to LSU AgCenter's study about insulating floors in homes with open crawlspaces. http://www.lsuagcenter.com/NR/rdonlyres/D33F711D-DC4B-4E4C-9ED6-A97DCE9DB026/79806/pub3187insulatingraisedfloorsHIGHRES.pdf I plan to insulate my floors with closed cell 3" everywhere...not average fill. once floor in bathroom is replaced and plumbing is finished. your biggest battle is going to be getting 3" everywhere, and not just averaged fill. plan to crawl under house before they leave. take a piece of wire with inches marked on it and a can of spray paint. have them come back and touch up low spots. knowing the foam companies you'll have to deal with, plan on double checking the work and not relying on their word that it is right. understand that closed cell is about R-7 per inch so 3" is R-21. actual R-values not quanitive values are what is important. best of luck.

Thanks for the replys. Forgot to add that the firm that wants to do closed cell + fiberglass said it was a code requirement to cover the foam with what he called a code approved ignition barrier. I thought that any foam rated E-84 was OK by itself. Comments? One question I need to ask is why not just spray 4 inches of closed cell and be done it with. That should provide at least R-25. Compared to the inefective R-11 that was in there it would be a big improvement. One reason this may not be practical is it may require two passes as I'm not sure you can apply closed cell at a 4 inch depth in one pass due to excess heat generation and risk of self ignition. Two passes would add to the cost and most likely push it well above the open cell. As for converting the crawl space into a mini basement, I think the jury is still out on that one. If not done correctly I think the consequences are worse than leaving it the way it is now. I also think the cost would be much higher since you still have to insulate the foundation walls and completely seal the volume from the ground.