Heat loss through basement and foundation walls is often neglected, even in new houses. But in fact, in an otherwise well-insulated and tight house, as much as 20% of the total heat loss can occur through uninsulated foundation walls.
Types of Floors
Floor, Basement & Foundation Insulation
Heat loss through basement and foundation walls is often neglected, even in new houses. But in fact, in an otherwise well-insulated and tight house, as much as 20%* of the total heat loss can occur through uninsulated foundation walls. Insulating a home’s foundation, basement or floor is usually the second most cost-effective insulation project in a home.
If the basement or crawl space is unheated and you don’t have plans to finish it, you can insulate between the floor joists instead of around the perimeter walls. Use unfaced fiberglass batt insulation supported from below with wire mesh or held in place with pre-cut metal rods.
Also, insulate the rim joist, the area on top of the foundation where floor joists meet the rim joist. Fiberglass batts cut to fit snugly or pieces of rigid insulation can be fitted into the rim joist area. Check local recommendations on vapor barriers. In most climates they should be installed facing toward the living space, so under the house, faced batts would have their facing up and the unfaced side exposed. In crawl spaces, cover the ground surface with 6-mil-thick polyethylene and anchor it in place to keep moisture from getting into the crawl space from the ground. Be sure the crawl space is well ventilated to keep moisture from building up and damaging building materials.
In a closed crawl space, insulate either the floor under the first story or the crawlspace walls. To insulate the walls, fasten insulation blankets to walls with nailed strips of wood.
If the basement is heated and used, you need to insulate the basement walls instead. The simplest method is to build 2 x 4 frames against the concrete foundation walls, insulate with fiberglass batts or blown rock wool, and cover with drywall. Before insulating, correct any drainage problems on the exterior if water leaks into the basement.
You should also insulate floors above unconditioned areas like a garage. We recommend R-19 for floors, or local building codes, whichever is higher.
A participating contractor will be able to help you determine what kind of insulation can help maximize your energy savings.
* Source: EnergySavers.gov