Fenestration refers to the openings in the building envelope, including the installation of windows, doors, and skylights. The inclusion of windows and other openings in the home are necessary as they improve the overall environment inside the home, however they do work to break the seal of the home, providing possible places for air, water, and cold air to enter the home. Thus, the number of openings included in a home must be taken into account, as well as the quality of the materials used to create these openings along with the placement.

Figure 1. Windows, doors, and skylights are all vital components of the building envelope. The process of including these openings in the building envelope is known as fenestration.[1]

Guidelines for how a home must include windows and doors varies across Canada. For colder regions, the necessary factors for a window or door to be considered energy efficient are more strict. In these cold, northern regions windows can only have a maximum U-value of [math]1.20 \frac{W}{m^2K}[/math] whereas warmer regions can have a u-value of up to [math]1.80 \frac{W}{m^2K}[/math] and still be considered energy efficient.[2] Generally speaking a lower U-value indicates a higher level of insulating power. Due to varying rules, regulations, and environmental necessities it is important to do research to ensure that the windows and doors installed in a home are suitable.

Benefits of Fenestration

The inclusion of openings in the building envelope is necessary for people to live comfortably inside a building (or even get in and out of them in the first place). Openings such as windows allow natural light into the home and can promote passive solar heating and cooling, as well as providing natural points of ventilation, air circulation and fire exits. Doors are also vital to a buildings design to provide a point of entry and exit to the building. Skylights provide similar benefits as windows, however they generally do not open. Aside from the increased energy efficiency, benefits of fenestration include:[3]

  • Increase comfort by reducing drafts and making a house feel warmer during the cold season.
  • Improve indoor air quality by reducing condensation, preventing mold growth. As well, a tighter seal into the home prevents external contaminants from entering the home.
  • Saving money by minimizing air leakage, improving the performance of furnaces and air conditioners, and improving the thermal performance of windows.
  • Control condensation due to the fact that energy-efficient windows stay warmer on interior surfaces, allowing for a higher level of relative humidity without condensation. This in turn allows windows to last longer, decreasing the need to replace them as frequently.

Issues due to Fenestration

All fenestration products experience a degree of heat loss due to:[4]

  • Radiation: heat energy is absorbed by the material of the door or window and radiates toward the cooler side.
  • Conduction: heat energy moves through the solid materials that make up the frame or other parts of the window, door, or skylight.
  • Convection: heat energy is transferred to the air between parts of the window or door.
  • Air leakage: heat energy is transferred to air moving through seals or gaps in the door or window

The first issue in this arises due to improperly installed windows, doors, and skylights. When large drafts enter a home it can lead to overworked heating or air conditioning systems as outside air penetrates the building envelope, allowing untreated air to flow into the home.[5] A simple way to check for leaks such as these is to hold a candle or lit stick of incense around the frames of doors, windows or skylights. If the smoke swirls, it indicates a draft point.[6] Weatherstripping, caulking, and high-efficiency fenestration products may be used to increase the seal of the window or door and decrease the costs due to air leakage. As well, windows, doors, and skylights that let air in can also let water in. This leads to condensation and mold. Poorly sealed windows and doors can also let in noise and dust, negatively affecting air quality in the home.[5]

The second issue with including windows, doors, and other forms of fenestration is that simply including these products decreases the efficiency of the insulation in a home. By putting in a window of a door and removing part of the insulation in the wall of a home, the effective R-value of that wall is reduced. This leads to a reduced ability to resist the flow of heat within a home. To avoid this it is vital to ensure that quality insulation is used and installed properly.


  1. "Building Envelope" by Augustine Musa.
  2. National Resources Canada. (March 28, 2015). Energy Star Qualifications [Online]. Available: http://www.nrcan.gc.ca/sites/www.nrcan.gc.ca/files/energy/pdf/energystar/Fenestration-Spec-E-Residential-October-2010.pdf
  3. National Resources Canada. (March 28, 2015). Improving Window Energy Efficiency [Online]. Available: http://www.nrcan.gc.ca/sites/www.nrcan.gc.ca/files/energy/pdf/energystar/IWEE_EN.pdf
  4. National Resources Canada. (March 28, 2015). Fenestration Technology (Online). Available: http://www.nrcan.gc.ca/energy/products/categories/fenestration/14432
  5. 5.0 5.1 Natural Resources Canada. (March 28, 2015). Fenestration as a System [Online]. Available: http://www.nrcan.gc.ca/energy/products/categories/fenestration/13937
  6. The Home Depot. (March 28, 2015). Draft-Proof Your Home [Online]. Available: http://www.homedepot.ca/eco-options/how-to/energy/building-materials/project-draft-proof-your-home

Authors and Editors

Bethel Afework, Jordan Hanania, Kailyn Stenhouse, Jason Donev
Last updated: May 11, 2018
Get Citation