High-latitude Challenges: Designing for daylight

Photo © BigStockPhoto.com

By Andy McNeil
Daylight and view consistently rank high on a list of desirable attributes in homes, schools, and workplaces. Delivering them, however, can be challenging, as there are often competing interests. In an urban context, for example, site constraints often affect building shape, which might force façade orientations problematic for harnessing daylight. For example, downtown Vancouver’s street grid is 45 degrees north, the least desirable orientation for daylight. Another consideration is the developer’s desire for maximum leasable floor area, which can increase the depth of floor plates, another factor impeding daylight. Buildings designed to maximize daylight and views are also negated by blinds and shades that are pulled down to block glare and often remain in that position.

Daylighting rules of thumb providing basic advice for shading elements on various façades focus on the middle latitudes, leaving out advice for equatorial and for higher latitudes. Daylight design for higher latitudes must be tweaked in order to optimize effective daylight and account for many factors, including:

  • low sun angles;
  • summertime sun reaching further north;
  • high occurrence of overcast conditions; and
  • cooler climates.

For example, a common rule of thumb is to provide fixed horizontal shading elements such as overhangs and light shelves on south-facing façades. However, this rule fails in northern locations as fixed horizontal shading elements perform poorly against year-round, low-angle sun. Automated fabric shades or venetian blinds are more suitable in the north. In equatorial locations where the sun is only low at sunrise or sunset, vertical shading is a better option on a south façade for the purpose of blocking the rising or setting winter sun.

Latitudes and sun angles
Major Canadian cities range from latitudes of 43 degrees north (Toronto) to 53 degrees north (Edmonton). These latitudes are comparable to European cities, but Canada does not experience the warming effect of the North Atlantic Ocean currents. For example, Edmonton and Hamburg, Germany, share the same latitude, while Vancouver’s is similar to Munich. Despite the climate differences, one can draw daylighting design inspiration from central European cities, particularly from the methods employed for shading low-angle sun.

The term ‘solar altitude’ refers to the angle between the sun and the horizon. The lower the solar altitude, the deeper the sunlight penetrates a building. Low-angle sun is a major cause of glare in office buildings because of the depth of penetration. Cities at all latitudes experience low-angle sun on east and west façades during sunrise and sunset. West-facing façades, in particular, suffer from direct glare because the low-angle sun coincides with the time a building is occupied. For this reason, designers from around the world have put more effort into identifying shading solutions for the west façades. In Germany, designs commonly employ motorized venetian blind systems on the exterior of a building—they can tilt, raise, and lower as needed to block the sun, as well as retract to admit diffused light into a building.

Higher-latitude cities experience low-angle sun on the south and north façades as well. In the winter, the sun stays very low throughout the day at high latitudes and shines mainly on the south façade. On December 21—the shortest day of the year—the solar altitude never exceeds 24 degrees in Toronto and 14 in Edmonton. During the winter, office buildings in Canadian cities require shading solutions on south-facing façades to mitigate glare from direct sun. In the summer months, the setting sun is situated to the northwest, shining deep into the north façade of a building. Glare from the setting sun is an issue for employees working into the evening.

Canadian cities also experience frequent cloud cover. Overcast conditions mean diffuse daylight providing excellent levels of glare-free illumination, if shades are raised and blinds are left open. Field studies, however, have shown manually operated shades are unlikely to be raised on overcast days. Occupants often lower shades to mitigate glare on a sunny day and leave them down indefinitely. One of the biggest obstacles to daylight is allowing shades to remain lowered when not needed.

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