The building envelope is the physical barrier between the exterior and interior environments enclosing a structure. Generally, the building envelope is comprised of a series of components and systems (see figure 1) that protect the interior space from the effects of the environment like precipitation, wind, temperature, humidity, and ultraviolet radiation. The internal environment is comprised of the occupants, furnishings, building materials, lighting, machinery, equipment, and the HVAC (heating, ventilation and air conditioning) system 
Improving the building envelope of houses is one of the best ways to get better energy efficiency.
A building envelope serves many functions. These functions can be divided into 3 categories:
The building envelope includes the materials that comprise the foundation, wall assembly, roofing systems, glazing, doors, and any other penetrations. The connections and compatibility between these elements is critical to ensure that the building envelope functions as intended.
The foundation is the structural component that transmits the loads from the building to the underlying substrate. Typically, some combination of reinforced concrete walls, slabs, and footings constitute the structural components of the foundation. However, the foundation must also be designed to control the transfer of moisture and thermal energy into the interior space.
The transfer of thermal energy through the foundation can be controlled by providing insulation between the interior and exterior environments; however, in some cases the foundation insulation is neglected to reduce construction costs.
Waterproofing the foundation is typically completed by applying a liquid applied asphaltic damproofing. Additional waterproofing products such as sheet-applied membranes, liquid membranes, cementitious waterproofing, and built-up systems are also viable options.
Drainage around the perimeter of the foundation must be provided to prevent long-term underwater submersion of the waterproofing membrane. One example of a perimeter foundation drain is weeping tile placed in trench complete with gravel ballast backfill, also known as a french drain. In some cases, a sump pit and pump system will be required in addition to the perimeter drain.
The wall assembly consists of a system of components that fulfill the support, control, and finish function of the building envelope. While the precise placement and configuration of each component may vary between climates and individual buildings, the following components are typically found in the wall assembly (from exterior to interior):
The roofing system is an important part of any house, as it keeps weather out. It consists of shingles on the outside, which are on top of tar sheeting as a vapor barrier. Inside of the tar paper is wood sheathing. Beyond this, the attic areas in most houses are insulated with fiberglass spray insulation. It tends to be fluffy, pink fiberglass. Inhaling fiberglass is extremely bad for a person's respiratory system, so it is important to wear a mask if this insulation type is in one's roofing system.
Doors are included in the housing envelope as they tend to be the biggest holes in the envelope. Having outer doors that seal well drastically improves the thermal efficiency of a house.
Changing the design of a house can drasitally alter its energy efficiency. See energy efficient building design to learn more or explore one of the pages below: