By definition, the building envelope (or building enclosure) is the physical separation between the interior conditioned areas and the exterior environment space of a building. The envelope serves as the outer covering (shell or skin) to help maintain the indoor environment together with the mechanical conditioning systems and to facilitate its climate control. The building envelope must be carefully designed with regard to site specific climate, ventilation, and energy consumption within the structure. The design is a specialized area of architectural and engineering practice that draws from all areas of building science and indoor climate control.
The physical components of the envelope include the following features/systems:
- Foundation – the lowest and supporting layer of a structure
- Walls – vertical structure, usually solid, that defines and sometimes protects an area within or around a structure
- Doors – opening or closing structure used to block off an entrance consisting of an interior and exterior facing sides
- Windows – opening in a wall, door or other vehicle that allows the passage of light and, if not closed or sealed, air and sound
- Roof – the covering on the uppermost part of a building or shelter providing protection from the weather, notably rain, but also heat, wind and sunlight
Some finish materials including decorative façade items are not usually considered a part of the envelope. However, insulation, building paper, flashing, exterior wallboard, most claddings and other components aimed at controlling moisture and airflow are typically included in the building envelope design.
There are four basic ‘control’ functions for good building envelope performance:
- Rain control – Control of rain which penetrates walls and roof surfaces is most essential, with numerous strategies that provide deflection barriers, drainage/storage/exclusion walls and moisture drying systems
- Air control – Control of air flow and pressure changes is important to ensure indoor air quality, control energy consumption, avoid condensation and thus help ensure durability and comfort
- Heat control – Control of air movement through the enclosure or through components of the building envelope (interstitial) itself to regulate temperature
- Vapor control – Control of vapor (moisture and humidity) in the crawlspace and attic space is fundamental in most climates, but is more demanding in cold climates and hot-humid climates
Building envelopes are often characterized as “tight” or “loose.” A tight envelope is precisely constructed to allow relatively few air leaks. This often requires significant quantities of insulation, caulk, sealants, and energy-efficient windows to create a tight shell for the building. Whereas loosely-constructed envelopes allow air to flow more freely from the exterior to interior spaces. A loose envelope may be created by design, or may be the result of poor construction techniques. Many experts question the benefits of tight versus loose building envelopes. When evaluating a building envelope, an analysis of infrared images can be very useful in identifying moisture issues from water intrusion, or internal condensation. Also, when looking at the efficiency of your home’s building envelope performance not only from a structural integrity standpoint, but from a performance in terms of how the house behaves relative to variations of inside and outside temperatures, changes in weather conditions as it relates to relative humidity, rain, snow and other forms of precipitation of all these factors, which lead to a higher and healthier building envelope efficiency.
Allan Abbata is a senior consulting engineer at Warren and a licensed professional engineer in South Carolina, North Carolina, New York, New Jersey, Pennsylvania, Massachusetts, Missouri, Texas, Alabama, Maryland, Minnesota and Virginia. Allan holds a Bachelor of Science in Civil Engineering. He has more than 40 years of applied engineering expertise to include in-depth knowledge of building codes, rules and regulations that guide design. Allan has also prepared construction drawings and specifications, provided on-site supervision and inspection of construction projects, and. has overseen project management and responsibility for overall performance of building contracts while also serving as the client’s liaison with local, state and federal agencies and municipalities.