Building Envelope
The building envelope is the term used to describe the shell of your home—your primary protection from the outdoor elements. The building envelope includes the roof, outer and inner walls, foundation and floors, windows and exterior doors. The protection the building envelope provides from the outdoor elements is referred to as a thermal boundary. The thermal boundary is created through use of insulation and an air barrier. Any improvement you make to your home affects your home's building envelope.
Insulation is measured in terms of R-value. Different types of insulation have different R-values, and the total R-value is measured by taking the thickness in inches of your insulation and multiplying by the R-value per inch of your insulation type. The higher the R-value of a material, the greater its insulating properties and the slower the heat flows through it. For example, Texas state building code requires a minimum R-value of R-32 in an attic. For the best efficiency, Current Energy recommends using at least R-38 in the attic. (The Department of Energy website lists recommended R-values for the different regions of the country.) The insulation is installed in walls, over ceilings, under floors, and between rooms, and is further discussed throughout this website.
The air barrier is created by the interior and exterior sheeting material. Most homes in the U.S. use drywall as the air barrier. Modern homes have many holes that create areas where the insulation and air barrier may not be continuous. This allows pockets of outside air into the building. This makes your air conditioner work harder in the summer, and creates drafts of cold air in the winter. For the best efficiency in your home, make sure any areas in your walls where there are holes are well sealed. This includes plumbing pipes, electrical outlets, switches, vents, overhead lights, fireplaces and cable connections. Switch plates, caulk, and insulation are all used to keep your home well sealed. Areas around windows and doors are often responsible for allowing air infiltration. Sealing these openings with caulk and weather stripping can significantly reduce infiltration. This process is called weatherization.
When weatherizing a home, air infiltration should be considered beyond the typical insulation and caulking around windows and doors. This includes sealing baseboard trim, plumbing bypasses, installing insulating pads behind outlets and switch plates, installing energy saver outlet caps in unused outlet plugs, and using an Attic Tent to seal attic entrances. Any fireplaces should have a working damper that produces a good seal and is closed when the fireplace is not in use.
One of the ways to determine if your home is tightly sealed is to have a home analysis and blower door test performed. A blower door test is done by a trained professional who attaches a variable-speed fan to an exterior door of the home. All other doors and windows are closed. The machine creates a low pressure in the home, which causes air to flow into the home through any leaks or cracks in the building envelope of the home. A pressure gauge connected to the blower door determines the rate of air flow into the home, and the professional performing the test then moves throughout the home to determine where the areas of air infiltration are.
Another factor to consider is the U-factor of the doors and windows of your home. U-factor is a measurement of how well a building material keeps the heat inside of a building or home. Unlike insulation’s R-value, where higher is better, the lower U-factor means a better resistance to heat flow the better insulating value.
For more information about home efficiency and how Current Energy can help or to schedule an Assessment, please visit our Home Assessment page.
