Daylight and Sunlight

by Joel Loveland

Before you even think of all the features you want in your house, think of site placement in relation to the sun.

A simple house like this one can work well or poorly, depending on it's orientation to the sun.

Daylight, the diffuse light of the overcast sky, is the same no matter how the home is oriented. It is soft, cool in both temperature and color, and difficult to bring deeply into the home. We think of it as the winter gloom typical of places in the Pacific Northwest where the sky is blanketed by clouds. Sunlight, as the name implies, is the direct rays of the sun. It brings to mind the white-hot skies of Arizona and the great Southwest, as well as light at the beach. The rays are directional, much warmer in both temperature and color, piercing, and very strong.

Homes are often located in places where one of these two conditions seems to predominate. In Seattle, for example, residents experience 200 overcast days per year, while Phoenix keeps its sunny demeanor from January through December. But even in these extreme climates, as well as in places that have more variation, the reality of the daily patterns of sunny and overcast vary widely week to week and even hour by hour. The cover of the sky is extremely dynamic, with the sun varying seasonally toward the north or south and daily from the east to the west, and the cloud cover often changing from one moment to the next. This sprightly quality of light brings drama into our lives, and, whether we intend it to or not, into our homes, via its windows, skylights, and glazed doors.

Window Choices for the Right Light

What can an architect, home designer, or lighting specialist draw from this state of affairs? What are the advantages and liabilities of a particular location as defined by its climate and sky conditions, when considering the design and construction of a home? The most important factors are the home's orientation and the number, size, location, and placement of the windows.

Designing for Overcast Light

A home that is planned and built to respond to a predominantly overcast sky has generous areas of window to gather the reticent luminance, and light-colored interior surfaces to draw the soft light inward. Its rooms are rarely more than twice as deep as the height of the window, and there are almost always windows on two sides of the room. Life in these homes is lived "on the edges", while closets, storage, stairs, and hallways are moved to the interior.

Bringing light deep into a home ("deep" being more than twice the height of the window) is often thought of as the job of a skylight. But because it is often horizontal or nearly horizontal within the plane of a low-sloping roof, a skylight is generally a poor way to bring deep light into the core of a home. Most skylights are extremely glare prone, and they gain a huge amount of heat in the summer, due to the high-altitude angle of the sun. They also lose a lot of heat in the winter, since heat rises in the warmest parts of the house and concentrates in the skylight well. The skylight becomes a chimney for the warmest air in the home during the coldest time of year.

The best way to bring light deep into the core of a home is to use dormer or clerestory windows on the roof, oriented according to whether you do or don't want heat gain during the winter. These windows should be oriented north or south, for uniform light. Select north for cool, blue, diffuse light with little heat gain; or south for warm, direct, and penetrating light, hot sunlight, and space heating. A well-designed vertical clerestory "skylight" can be a real asset to a home, especially in those deep recesses away from the window wall.

Designing for Sunlight

Homes built to respond to sunshine are entirely another matter. Here, orientation is to the seasonal and daily hemicycle (the traveling pattern of the sun's rays). In designing for sunlight, pay specific attention to climate and to the orientation of the window walls.

In a home, the windows are the greatest source of heat gain during the day--they are helpful in a cold climate or during the coldest time of year, and can be disastrous in a hot climate or during the hot season. If the weather is hot and sunny all year long, as it in much of the southern United States, or during the summer months as in much of the rest of the country, a home should be designed to avoid the sun, opening to the north and avoiding exposure to the east. In such a home, the sun is welcomed on the southern exposure only on the coolest of winter days.

In the half to two-thirds of the lower 48 states where winters are cold to very cold and summers are warm to very warm, windows play an important role in defining the experience of being indoors and in helping to determine heating and cooling needs. Because windows are the least insulated and most visible light-transmitting part of the building surface, they mediate between a wide range of inside to outside temperatures, and extremes of visible light. The seasonal range of extremes of temperature and visible light, compounded by the effects of the hour-by-hour differences in direct exposure to the sun, make paramount the consideration of windows in the design and construction of a home.

House Plan and Orientation

Take a simple house plan with a front entry door to the street face; a garage to the left; bedrooms to the right; and family cooking, eating, and interior and exterior living spaces to the rear. The front door and the driveway/garage door on the long side of the front of the home are dominant in establishing the placement, and therefore the orientation, of the living spaces. The garage covers one end of the home, greatly limiting the possibility of a windowed wall, while the bedrooms dominate the opposite end. The garage end of the house is windowless to the house interior, while the bedroom end is generally not occupied during daylight hours.

The orientation of the street, the placement of the home on its lot in relation to the street, and the house design all interact to determine the placement of the windows. The driveway, the garage, and the front door establish the potential role that windows can play in providing the interior experiences of light. These experiences of light greatly influence the patterns of daily life in the home. The placement of windows also shapes the home's demands for heating and cooling. What happens when a home builder or buyer fails to take these factors fully into account?

Facing North

Take our simple floor plan and place it on the south side of a street that runs east to west. The garage and the front door are on the north side of the house, with the garage to the left (east) of the front door. The living spaces are on the south side of the house, and the bedrooms are on the west. This home has a deeply shaded north-facing front entry, which is covered with ice and snow for much of the winter. This entry is cold and shaded during the spring and fall, and cool during the summer. In the winter, the southern living spaces are bright, sun-filled rooms. The low southerly winter sun penetrates deeply while these interior rooms remain relatively cool in the summer, since almost all of the light from their south-facing windows comes from a very high angle in the sky. This is especially true for homes located in the more southerly and warmer latitudes of the United States. The south-facing windows would be cooler yet if the proper deciduous trees were planted to shade them. The bedrooms to the west are dark and cool or cold in the mornings, and bright and warm or hot in the afternoons. Shading the west windows with overhangs, a trellis, or a tree would help to temper the glare and heat. The garage is bathed with sunlight all morning long, a waste of light.

Facing South

Now, flip the house to the other side of the street. The living spaces and the generally larger windows or glazed doorways dominate the northern exposures, where cool, diffused light and cool-to-cold temperatures predominate. The public face of the home, less frequently occupied and usually with less window area, is now exposed to the bright winter sun. The bedrooms are bright with early morning sunlight. In summer, the garage now buffers the house from the blazing afternoon.

Facing East or West

Now, imagine rotating the street 90° so it runs north to south. The home rotates 90° to the patterns of sunlight. The bedrooms and garages move to the north or south orientations. The front entry and the living spaces now face east or west.

The experience of light, heat, and cold in the home is once again altered dramatically. If the living spaces face east, they are bathed in morning sunlight; in the afternoon, they are shuttered in deep, cool shade. If they face west they will overload the house with heat on summer afternoons.

On to the Next Steps

Once one has taken as much advantage of the patterns of natural light as possible, it is time to carefully consider the available window technology. The right kind of technology can turn a natural light liability--dark, cold, and drafty or overwhelmingly bright and hot--into at least a minimal problem, if not an asset, (see "Today's Wonderful Windows," p. 13).

Joel Loveland is a an associate professor of architecture at the University of Washington and a daylighting consultant at the Lighting Design Lab in Seattle, Washington. He can be reached at Tel: (800)354-3864, Ext. 32, or 206-325-9711, Ext 32.

For more information: Lighting Design Lab, 400 E Pine St., Suite 100 Seattle, WA 98122. Fax: (206)329-9532, Ext. 32; E-mail: joel@northwestlighting.com; Web site: www.lightingdesignlab.com. Further Reading Designing Low-Energy Buildings: Guidelines with Energy-10 Software. Washington, DC: National Renewable Energy Laboratory, 1996. Available from SBIC, 1311 H St. NW, Suite 1000, Washington, DC 20005. Tel:(202)628-7400; Fax:(202)393-5043. Cost: site-license $500, professionals $250, SBIC members $175, students and professors $50.

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