The amount and quality of daylight are constantly changing and influenced by various factors such as location, weather, time of day, and year. This variability can make it challenging to incorporate daylight into architectural design intuitively and effectively. This series aims to introduce orientation as a principle of daylighting design and provide insight into the different qualities of light based on the direction of the sky. While the content draws primarily from Switzerland's latitude and pre-Alpine climate, the principles can be applied to any location with an understanding of the site, sun chart, and local climate.
Direct sunlight from the south is a very intense and directional light source. It creates sharp-edged shadows, which in turn create high contrast between light and shadow. It makes the space appear more vivid, modeling surfaces and objects. Characteristics are blocks of light that are projected onto the surfaces of the space as they enter through the façade and move over time across the walls, floors, and furnishings. Southern light is a powerful light and therefore also comes with glare and radiant heat.
Which rooms benefit from a south-facing orientation?
Southern exposure is often the preferred orientation and several good reasons exist. Rooms that receive direct sunlight look bright, open, and dynamic, creating an attractive and pleasant atmosphere. Sunlight from this orientation is ideal for our living spaces, and areas we spend most of our time and want to enhance the quality of our stay throughout the day. Additionally, rooms with southern exposure offer an excellent view of the sun's path, which creates a stronger connection to the outdoors and gives us a sense of space and time.
In hospitals, shortened lengths of stay ¹ and lower consumption of pain medication ² have been demonstrated due to better daylight conditions. High illumination levels of daylight and an unobstructed view of the outside have a positive influence on our attention, performance, well-being, and health. Particularly in patient rooms and general lounge areas of hospitals and other healthcare facilities, it could therefore be beneficial to be located on a south-facing facade, in order to ensure high levels of daylight illumination and a strong connection to the outside space in the course of the day.
Should all rooms face south?
Actually, no. There are certain areas where the strong, direct sunlight that creates harsh shadows is not ideal, such as artists' studios and galleries. In any building, there are areas where southern light would not be utilized, such as storage rooms, garages, or spaces with lower quality stay requirements, or where light is not desirable at all. Additionally, it is crucial to control direct sunlight and eliminate glare in areas where people read, write, or work on screens.
What should be considered when planning rooms on the south facade?
When planning rooms that face south, it's important to take into account the radiant heat that comes in with the sunlight. This heat can cause rooms to overheat during summer months, so it's important to properly control the amount of daylight that enters based on the time of day and season. Shading is an effective way to control the amount of sunlight that comes in, and it's relatively easy to achieve on a south-facing façade due to the high position of the sun.
Horizontal shading elements in the form of eaves, balconies, cantilevered façade elements, pergolas, and other roof structures protect against the high summer sun. Overhead shading elements intercept the direct rays of the sun but allow diffuse daylight to enter the room and provide an unobstructed view. In winter, thanks to the low position of the sun, the sun's rays penetrate deep into the room and warm it up. In our latitudes, the lintel angle of balconies or canopies on south-facing facades should be > 30° degrees to avoid excessive shading in the winter months.³
Le Corbusier introduced the concept of the "brise-soleil", literally the sun breaker, to modern architecture in the 1930s: a static shading element that seasonally shades a window or lets the sun in. Static shading systems are mainly useful at latitudes between 25° and 50°. Near the equator, the sun is usually high enough that all windows benefit from a small overhang, but at higher latitudes, the sun is often so low in the sky that horizontal shading would have to be very large to be effective.⁴
Temporary shading elements can also be considered for external sun protection. In our latitudes, they operate from about April to October and can be retracted in the winter. A retractable canopy or articulated arm blinds are possible variations of these. Dynamic (movable) shading elements such as Venetian blinds or roller shades serve the same purpose as their static counterparts, but they are dependent on user behavior and have an impact on visual comfort, as they are often also effective as glare protection.
Besides overheating, glare from direct sunlight must be limited. Especially in working rooms and in rooms where the position and viewing direction are not freely selectable, it is important to control glare. In addition to external sun protection, internal glare protection can be helpful. This allows for the use of heat radiation in winter while preventing glare.
Glare is not only annoying when the sun shines directly into your face or eyes. Reflected sunlight on room or table surfaces can also lead to strong contrasts and glare. To prevent this from becoming an issue in offices and workspaces, it's important to not only shade workstations but also ensure an even distribution of daylight throughout the extended field of vision. When facing south, be cautious of highly reflective outdoor surfaces such as water or lower-lying roofs that may reflect the sun into rooms.
Summary
Sunlight from the south is strong and intense. It creates short, sharply drawn shadows with high contrast.
Main living areas, patient rooms, and rooms with a high quality of stay are spaces that thrive on experiential sunlight and are well situated on the south facade.
Design facade openings so that they let in diffuse light and the view allows a visual connection with the outdoor space.
Horizontal shading elements intercept the rays of the high sun. Ideally, these are sized to shade the intense summer sun and let in the low winter sun. An additional interior glare shield also protects against glare in winter.
Are you interest in daylighting strategies for other orientations? Here are the links to the articles:
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This series was inspired by Amelia Lee's podcast Undercover Architect S1 Ep.2-5. I would like to thank the architectural firms and photographers who allowed me to use their work as sample projects.
Sources
1/ Choi, J. H. Beltran, L., and Kim, H. (2012). Impacts of indoor daylight environments on patient average length of stay (ALOS) in a healthcare facility. Building and Environment; 50, pp. 65-75.
2/ Walch, J.M., Rabin, B.S., Day, R., Williams, J.N., Choi, K., and Kang, J.D., (2005). The effect of sunlight on postoperative analgesic medication usage: A prospective study of spinal surgery patients. Psychosomatic Medicine. 67(1). pp. 156-163.
3/ Rüedi A., Schürch P., Watter J. (2016). Solararchitektur - Häuser mit solarem Direktgewinn (1. Aufl.). Fachhochschule Nordwestschweiz, Institut Energie am Bau.
4/ Reinhart C. (2020). Daylighting Handbook I – Fundamentals Designing with the Sun (2nd Edition). Building Technology Press.
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