I would use unfaced. I would buy as a roll (not precut batts) and cut you own 5 ft pieces.

Nice article worthy, thanks for that... I love this part... "DonâÂÂt vent dryers or other appliances into the crawl" Who would do that? Every load of washing machine water direct into your crawlspace. Sheesh. For closed conditioned crawl spaces the recommendations were... â¢Insulate the perimeter walls to the level suggested for above-grade walls in your climate. â¢Exterior perimeter wall insulation is a good option to consider, especially in new construction. It eliminates the problems of moisture management associated with interior wall insulation and provides the possible benefits of additional thermal mass within the structure. The downside is you have to protect the insulation from termites and the above- grade portion of the insulation from deterioration caused by weather exposure. â¢When insulating a crawl from the interior, you should protect rim joists from condensation with foam insulation. â¢Use water-resistant insulating materials, such as rigid-foam board or spray foam properly protected to meet fire ratings. Avoid using air-permeable insulation, such as fiberglass batts or spray-on cellulose. â¢Power venting a sealed crawl space to the exterior can reduce the movement of air from the crawl space into the house. This can improve IAQ, but at the added cost of operating and maintaining the exhaust fan. I just might do that. i.e. insulate the walls and rim joists cuz our floors over the crawl space zone of the house are really cold in the winter. The issue there is "properly protected". Per the fire ratings, XPS sheets are to be covered w drywall or finished. Obviously a crawlspace you're not going to finish in drywall like you would a full height basement. So they don't really address what to do there -- cant leave it exposed but you're not gonna frame and finish... Thoughts?

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.