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MARCH 2014 MEETING - "Daylighting Strategies - When the Whole Window is a Wall"

The March meeting of the BEC was co-presented by Kera Lagois and Keith Yancey of Lam Partners in Cambridge, MA. Focusing on the topic of daylighting, Ms. Lagois and Mr. Yancey discussed various issues with respect to building facades with large percentages of glazing. Well-attended by industry professionals, this meeting was a continued success of the BEC’s 2014 Lecture Series on glass enclosure design.

Experts in the field of lighting design, Ms. Lagois and Mr. Yancey noted the balance between the benefits and “costs” of daylighting. Large glazing areas certainly offer great views, and subsequently higher worker performance, however this comes at the cost of potential issues with excessive glare and solar heat gain if not properly accounted for. A number of illuminance-based metrics exist to evaluate both the amount and usefulness of daylight. These metrics account for fluctuating climate changes throughout the year, and are a valuable tool in determining if shading is required and what shading strategy will be most effective.

An example case study was presented to contrast the performances of a glass façade with no shading provisions, external light shelves, and external louvers. With regard to overall light levels, the external light shelves and louvers only showed 2% and 8% reductions, which likely will not provide a favorable cost vs. return on investment. However, upon evaluating useful light, external light shelves demonstrated a 4% increase, and louvers showed a 66% increase. Louvers proved to also be considerably higher performing in reduction of direct sunlight and glare, and were determined to be the favorable shading option for this particular case.

Overall it was concluded that, although visually and architecturally pleasing, highly glazed facades can potentially have a negative effect on the building’s interior environment. As a rule of thumb, it has been found that the optimal window-to-wall ratio is generally between 30% - 40%. Should this be exceeded, it is prudent to conduct a daylighting analysis to determine if shading provisions should be incorporated. 

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BSA BEC Presentation 3 - Daylighting Strategies - K. YANCY & K. Lagois- 3-24-2014.pdf2.62 MB