Our preference in this climate is to insulate the interior of a basement or crawlspace wall and rim joist with rigid insulation, and to keep these spaces isolated from outside air as much as possible.

To begin with, all dirt floors in these spaces must be covered with a vapor barrier to eliminate evaporation, which can place up to 1 gallon of water into the air of your home per 100 square feet of uncovered floor space.

Insulating the basement/crawlspace ceiling alone no longer satisfies code in most instances, and with good reason, as the results are usually poor. In the summer these areas are kept cool by the surrounding earth, and when warm moist air seeps in, the result is condensation on the walls and other surfaces, including the insulation between the floor joists, most often fiberglass, which then starts drooping from the weight. Venting at this time only worsens matters by introducing more warm, moist air. And in the winter, huge amounts of energy are lost through the masonry, which conducts heat almost as quickly as water.

(Condensation in this crawlspace caused mold and rot. A number of these floor joists had to be replaced.)

 (Crawlspace walls and rim joist insulated with foil faced Dow Thermax rigid insulation. Vapor barrier on the floor is fire resistant poly sheeting.)

Exterior insulation is definitely possible, but it can be difficult and expensive to install a meaningful amount. It complicates the problem of waterproofing, and may require cantilevered wall framing or some type of flashing that will protrude beyond the siding. It also has to be covered above grade with some sort of finish, usually rolled vinyl or stucco. Below grade protection is also necessary to protect from insects and other pests, which love to burrow and form tunnels in rigid insulation. The use of insulated concrete forms pose many of the same issue.

(One very good way to finish a basement, with continuous rigid insulation attached to the wall, before installing studs. The stud bays can then be insulated and walls finished.)

Insulating the interior of concrete walls places no practical limit on the depth of insulation used. Bayonet style hangers are used to install the rigid to the wall. Dow Thermax, which comes with either a foil or white face, can be installed in most states without an additional thermal barrier, such as sheetrock. Styrofoam may have to be coated with a fireproof paint if not covered with a finish wall. 

(Vapor barrier of thick sheet rubber attached to pressure treated 2”x4”. Rigid installation being installed using bayonet style hangers adhered to wall. Slip washers then hold the insulation in place.)

You should never frame a conventional wood frame wall directly alongside a below grade concrete wall and then install conventional insulation. Condensation will likely develop on the concrete wall and wet the entire assembly, causing mold and rot. We recently had to remove the sheetrock and insulation from a finished basement of a two year old house for this reason.

Insulating stone foundations can be done by installing a plastic membrane and then spray foam, followed by fireproof paint or a finished wall.