The building envelope includes everything that separates the interior of a building from the outdoor environment. It plays a major role in energy efficiency in both residential and commercial structures. Building structures retain or lose heat energy through conduction, convection and radiation. Conduction, or the resistance of the house to give up its heat, is affected by the building materials. How well materials such as insulation, brick, wood, concrete, and windows resist this transfer of energy is measured as the R-value. The higher the R-value, the lower the transfer of energy out of the house.

Convection is the actual movement of energy in and out of the structure usually through the movement of air. The tighter the envelope of the structure, the lower the convection factor. Windows and doors can be a major source of air leakage and their proper installation is a key factor in reducing the loss of heating or air conditioning from the home.

Finally, radiation is the inevitable loss of heat energy during the night when temperatures fall below the temperature of the inside of the structure. Well-insulated walls and double pane windows can protect the structure from heat loss during the night and loss of cool air during the day.

Conduction, convection and radiation are all at work in hot climates such as Texas. In our case, air conditioning systems must work harder to cool the house during hot weather if the heat from outside is entering the home due to poor insulation. Well-insulated structures retain air conditioning, while tight envelopes prevent the loss of cool air or infiltration of hot, moist air. There are many types of insulation available, and each has different insulating properties, expressed as R-values per inch. The amount of insulation a structure needs can be easily calculated using the recommended total R-value, which varies depending on the location and the specific part of the home or commercial building.

Additionally, when building new walls and ceilings, innovative advanced framing techniques help to achieve energy efficiency well beyond current traditional materials. Framing can be avoided entirely with Structural Insulating Panels (SIPs), the latest technology for achieving highly insulating walls and ceilings. The prefabricated panels sandwich a foam core between two sheets of plywood and are manufactured to precise design specifications. Insulated concrete forms, previously used only for foundations, are now also being used to form insulated concrete walls. Both methods can save anywhere from 15 to 50% on annual energy costs over conventional wood frame homes.

Finally, a wide variety of alternative materials is now available and are being used to construct buildings. Many of these materials are both energy efficient as well as environmentally friendly. These materials include adobe (clay and straw), straw bale, rammed earth and even tires and other recycled materials. One of the best websites to find information on efficiency ratings and facts on all of these materials is the Department of Energy’s Energy Efficiency and Renewable Energy site.