Air leaks reduce a home’s energy-efficiency. Air can leak through cracks or holes in walls, ceilings, floors, and around doors and windows. A typical house loses about one-third of its heat through this infiltration (outside air coming into the house) and (inside air leaving the house.) A tight house will reduce heat and air movement and be quieter and cleaner. The other two-thirds of heat movement occur by conduction through foundations, floors, walls, ceilings, roofs, windows, and doors. Good construction techniques cut energy losses. Energy losses can be reduced by.

• Installing continuous vapor retarders on walls and ceilings,
• Caulking any holes or cracks on the inside surfaces of walls and ceilings,
• Caulking around windows and door trim on the outside,
• Sealing around window and door trim, and electrical outlets on the inside,
• Sealing around any pipes or ducts that penetrate the exterior walls,
• Weather stripping windows and doors.

Heat flow in and out of the building from conduction can be reduced with high levels of insulation in the attic, sidewalls, basement walls, and doors. Windows should have a low U-value, and be concentrated on the south for solar gain.

Windows and doors

Substantial heat loss can occur through windows and doors. Glass is a poor insulator; the R-value for a single layer of glass is approximately 1. Total heat loss through windows depends on the location, number, size, and type of windows. A single north or west window in a room could lose more heat than the entire exterior wall. South facing windows can function as efficient solar collectors and result in a net heat gain during the winter. All other windows are net energy losers during the winter. Whenever possible, concentrate glass on the south, and minimize the number and size of windows on the other walls.

Use insulated doors and storm doors to minimize heat loss through entry doors. Such assemblies typically have R-values of about 10 or 12.

Controlling moisture problems

Seeing moisture problems early can prevent costly repairs and increase thermal performance. When sealing a house small details are important. A small area that is not insulated and sealed can lose large amounts of heat. Air leaks can carry moisture into the house framing, where it can condense and lead to discoloring of drywall, paint failures, or wood decay.

Vapor Barriers or Vapor Retarders

A vapor retarder is a specially treated paper, thin plastic sheeting, or low permeance paint that prevents condensation of water vapor inside wall or ceiling materials. This trapped moisture can cause damage to the wallboard and paint as well as structural deterioration.
The vapor retarder must have a vapor permeance (the rate that moisture can pass through materials) of not more than 1.0 perm (tested in accordance with ASTM Standard E96-80).
The term "vapor barrier", which is also commonly used, is somewhat misleading since it does not completely bar the transmission of water vapor. A vapor barrier is actually a vapor-resistant membrane, and is more properly called a "vapor retarder."

Location of Vapor Retarder
Interior moisture tries to move out of a building. Vapor retarders are important, because they keep this moisture in a warm area where it will not condense. For this reason, vapor retarders should be applied (in colder climates) behind the drywall of a wall or ceiling next to existing insulation and on the warm-in-winter side (between the insulation and the conditioned space) of insulated floor sections over crawl spaces.

Caution: Because moisture may be trapped between the two vapor retarders and eventually ruin the installation, if additional insulation is added during your remodeling project, be sure that a second vapor retarder is not applied between layers of insulation. There is a chance that this second vapor retarder might be added inadvertently during an insulation upgrade because some batt insulation comes with a vapor retarder integrally attached in the form of paper or aluminum-like sheeting.