The Engineer: Let There Be Daylighting
By David Heska P.Eng
Effective daylighting is not just about increasing the size of windows.
By David Heska P.Eng
With the shortest day of the year behind us, it only gets brighter from now until the summer. Today I would like to address a topic that directly impacts our glass industry but rarely gets the attention it needs.
Intrinsically, we all know that increased daylight results in increased happiness and comfort. We also know that people exposed to daylight are more productive, more efficient, miss less work due to illness and will be more creative. An American study found that a store’s sales index increased by an average of 40 per cent simply by adding skylights. For example, if a non-daylit store had average sales of $20 per square meter, sales would be $26 to $30 if skylights were added. Additionally, students in classrooms with the highest levels of daylight performed seven to 18 per cent higher on standardized tests.
The introduction of daylighting strategies can also considerably reduce a building’s electricity consumption. Consider the office I’m sitting in as I write this article. Ten years ago, WSP’s LEED platinum office in Kitchener, Ont., was constructed and named “A Grander View.” The energy intensity of the building is less than 70 kilowatt-hours per meter squared. Our designers recognized that one of the largest consumers of energy in a typical office is lighting. So, in addition to installing triple glazed, low-E, argon filled, fiberglass windows, the following three design features were also implemented:
- A long, skinny building was designed with a 12-meter-wide footprint enabling most interior spaces to benefit from windows on at least one external wall.
- A large skylight that provides natural light was placed in the central atrium and stairway.
- Meeting rooms have interior glass walls that allow light to pass through in order to brighten corridor spaces.
But effective daylighting is not just about increasing the size of windows. The quantity of glass is not always a direct measure of quality daylighting. We’ve all experienced poor lighting conditions when either direct beams of sunlight shine in our eyes or there is glare on our computer monitors. In these cases, daylighting is more of a hindrance than a help and people draw the blinds or cover the windows.
Previously I have written about the need to have reasonable window-to-wall ratios around 40 to 50 per cent. There are other design considerations that can help maximize daylighting. We should minimize the window area on the east and especially on the west elevation of buildings. Architects should consider the building orientation (if possible) and specifications should not restrict the design to one glazing type for all elevations. We can remove glass that extends below eye level since it provides little benefit to light levels. And we should increase the use of skylights, light tubes and clerestory windows, which are great design features anyways.
Many of the manufacturers listed in Glass Canada’s Buyers Guide have excellent products and unique coatings, films and frit patterns that can control glare and reduce solar heat gain. I encourage you to get to know them. As the days get longer I hope you enjoy the warmer weather and the productivity boost that comes with it.
David Heska, P.Eng. is a Director with WSP’s Building Sciences team in Southwestern Ontario. He oversees the operation of the Hamilton, Kitchener and Windsor offices. David has been involved on window simulation projects as well as the design and replacement of windows in commercial and residential buildings. He can be reached at David.Heska@wsp.com