Wall Mounted Air Conditioning Unit. In New Construction, adding insulation on the exterior of the basement walls will:

Minimize thermal bridging and reduce heat loss through the foundation. Protect the damp-proof coating from damage during backfilling. Provide some protection against moisture intrusion. Protect the foundation from the effects of the freeze-thaw cycle in extreme climates. Reduce the potential for condensation on surfaces in the basement. Conserve room area, relative to installing insulation on the interior. In an existing home, adding insulation to the exterior of the basement walls is impractical. Interior basement wall insulation has the following advantages:

 

It is much less expensive to install than exterior insulation for existing buildings. Almost any insulation type can be used. It eliminates the threat of insect infestation. It isolates the living space from the cooler earth more effectively than when exterior insulation methods. Here are a few things to consider when installing interior basement wall insulation.

Interior insulation reduces usable interior space by a few inches. It doesn't protect the damp-proof coating like exterior insulation does. If perimeter drainage is poor, the insulation may become saturated by moisture weeping through foundation walls. Superior air-sealing details and vapor diffusion retarders are important for adequate performance. To determine appropriate R-values for basement walls in your area, use these R-value recommendations. Then choose the type of insulation:

 

Blanket (batt and roll) insulation. Insulating concrete blocks (new construction) Foam board insulation. Insulating concrete forms (new construction). Loose-fill insulation (good choice for finished basements). Sprayed foam insulation (good choice for finished basements). Moisture control is particularly important for basements, because they are notorious for problems with water intrusion, humidity, and mold.

How you insulate a crawlspace depends on whether it's ventilated or unventilated. Most building codes require vents to aid in removing moisture from the crawlspace. However, many building professionals now recognize that building an unventilated crawlspace (or closing vents after the crawlspace dries out following construction) is the best option in homes using proper moisture control and exterior drainage techniques.

 

If you have or will have an unventilated crawlspace, the best approach is to seal and insulate the foundation walls rather than the floor between the crawlspace and the house. This strategy has the advantage of keeping piping and ductwork within the conditioned volume of the house so these building components don't require insulation for energy efficiency or protection against freezing. The downside of this strategy is that rodents, pests, or water can damage the insulation and the crawlspace must be built airtight and the air barrier maintained. It’s best to locate the access door to the crawlspace inside the home through the subfloor unless you build and maintain an airtight, insulated access door in the perimeter wall.

Insulating a slab in an existing home can be expensive and disruptive, but If the slab in your home is cold it is possible to dig around the perimeter of the house and install insulation, usually foam board. In most parts of the United States, insulating the exterior edge of a slab can reduce heating bills by 10% to 20%.

 

Installing slab insulation during the construction process is more straightforward. Slab insulation, typically foam board, is installed either directly against the exterior of the slab and footing before backfilling or under the slab and along the inside of the stem wall of the foundation. Construction details vary widely, so it’s best to consult a building professional in your area. Building America’s climate-specific publications also have useful construction details for different climate zones.