Building envelope

The building envelope is the physical barrier between the exterior and interior environments enclosing a structure.[1] 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 and equipment, and the heating, ventilation and air conditioning (HVAC) system.[2]

Figure 1. The components of the building envelope[3]

Improving the building envelope of houses is one of the best ways to get better energy efficiency.

Function

A building envelope serves many functions. These functions can be divided into 3 categories:[2]

  • Support: to ensure strength and rigidity; providing structural support against internal and external loads and forces.
  • Control: to control the exchange of water, air, condensation and heat between the interior and exterior of the building.
  • Finish: this is for aesthetic purposes. To make the building look attractive while still performing support and control functions.

Physical components

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.[4]

Foundation

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.[5]

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.[6]

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.[6]

Wall assembly

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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):[7]

  • Exterior cladding
  • Exterior sheathing membrane
  • Exterior sheathing
  • Insulation
  • Structural components
  • Vapour barrier
  • Interior sheathing

Roofing system

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.

Glazing

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Glazing refers to the panels in windows, doors and skylights - usually glass - that let light through.

Door

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.

Other penetrations

These may include a chimney, or vents for a dryer or stove.

Energy efficient design strategies

Changing the design of a house can drasitally alter its energy efficiency. Click here to learn more.

References

  1. C.E. Hagentoft, An Introduction to Building Physics, 1st ed. Studentlitteratur AB, 2001.
  2. 2.0 2.1 National Institute of Building Sciences. (March 22, 2015). Building Envelope Design [Online]. Available: http://www.wbdg.org/design/env_introduction.php#fap
  3. "Building Envelope" by Augustine Musa.
  4. Building Science Corporation. (March 22, 2015). The Building Enclosure [Online]. Available: http://www.buildingscience.com/documents/digests/bsd-018-the-building-enclosure_revised
  5. R. Neggers. "Building Envelope Considerations – Foundation Wall". Internet: http://www.ronneggers.com/building-envelope-considerations-foundation-wall/ [November 3, 2013].
  6. 6.0 6.1 A. Bredenburg. "Foundation Waterproofing Options". Journal of Light Construction. 33(1), pp. 20-24, March 1995.
  7. Building Envelope Corporation. "High R-Value Wall Assemblies". Internet: http://www.buildingscience.com/resources/high-r-value-wall-assemblies [November 3, 2013]

Authors and Editors

Jordan Hanania, James Jenden, Michael Lasby, David Paul, Pria Ghia, Barett MacLeod, Kailyn Stenhouse, Jason Donev