Von Löwen Designs

By cutting back on your requirements for electrically powered light, daylighting can considerably lower a home’s energy consumption. However, utilizing too much daylighting and over doing it, homeowners will have a strong possibility of increasing both their heating and cooling demands.

A balanced approach to daylighting involves a whole home design starting with the location and orientation of the house itself (if possible) and continues with proper room location and design, window sizing and placement, and selection of room finishes.

In addition to reducing the need for electric lighting, daylighting offers many less tangible health and productivity benefits. Studies have shown that high quality light elevates moods, reduces depression, and improves worker productivity and student test scores.

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-coloured 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.

Shape 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 homebuilder or buyer fails to take these factors fully into account?

Facing North.

Take this 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.

Decisions made early in the design process regarding building orientation, form, room depth and height, have a significant impact on the utilization of daylighting. Similar to a passive solar home, a house form that optimizes daylight in temperate climates will be roughly rectangular in shape elongated in the east-west direction. This allows a majority of the rooms and windows to face north and south while reducing the wall and window area facing east and west. East and west facing windows are difficult to shade in summer and can transmit excessive solar heat gain. Major living spaces that are most often used should be located along the home’s north and south perimeters adjacent to windows designed to transmit an appropriate amount of natural light.

Room Location and Design.

When laying out rooms on a floor plan, establish which spaces will most benefit from daylight and which spaces need little or no daylight. Rooms that require good quality lighting year-round should be placed along the north and south perimeters of a home. Living rooms, family rooms, kitchens, and bedrooms are examples of spaces that can greatly benefit from well-distributed natural light. Rooms that are less often used or have lower lighting requirements can be placed in the home’s interior. Laundry rooms, media rooms, and closets are examples of spaces that don’t need well-distributed natural light.

A room’s orientation makes a big difference in the quality of light it receives. Rooms facing north will receive fairly constant, indirect (or diffuse) daylight all year long. Rooms facing south will receive bright, direct sunlight all year. Ideally, shape and locate each room so that it receives natural light from two different directions. This will allow a room to be illuminated by both direct light and diffuse light at any given time of day.

For good light penetration, the depth of rooms should be kept relatively small adjacent to the wall or window that is the daylight source. A standard window can produce useful illumination to a depth of about 1.5 times the height of the window. For example, given a wall height of 8 feet and a window header height of 7 feet, a room should be no more than 11–12 feet deep for well-distributed daylight. As a general rule-of-thumb, the higher the window is placed in the wall, the deeper the daylight penetration.

To distribute natural light deep inside a home, consider interior glazing that allows light from one space to be shared with another. This can be achieved with transom windows above doors, vision glass, or translucent panels.

Window Location and Design.

The simplest way to provide good quality daylighting for homes is to place windows so that natural light enters every room from more than one direction. This strategy produces much less glare around people and objects than light from a single source does. Furthermore, more even distribution of light results in less contrast in the room as a whole, better illuminating otherwise dark surfaces and corners.

Punched window openings centered in a room, such as small, square windows separated by wall area, result in uneven illumination and harsh contrast between the window and adjacent wall surfaces. A better distribution of light is achieved by locating windows near ceiling and wall surfaces. By reflecting much of the light into a room off the ceiling and walls, the direct light becomes much more diffuse and reduces glare significantly.

Window frame materials should be light-coloured to reduce contrast with the view and have a non glossy (satin or matte) finish to eliminate glare spots. Light-coloured window jambs and sills can be beneficial light reflectors. Deep jambs should be splayed (angled toward the interior) to reduce the contrast around the perimeter of the window.

Room Finishes.

Once daylight enters a room, the surrounding wall, ceiling, and floor surfaces are important light reflectors. Using reflective finishes will better bounce daylight around the room and reduce extreme brightness contrast.

The most important interior light-reflecting surface is the ceiling. High reflectance paints and ceiling tiles are now available with 0.90 or higher reflectance values. Tilting the ceiling plane toward the daylight source increases the daylight that is reflected from this surface. In small rooms the rear wall is the next important surface since it directly faces the window. This surface should also be highly reflective. The sidewalls and the floor have less impact on how daylight is reflected throughout the space.

Other Strategies.

In addition to windows, three other architectural strategies should be considered for effective daylighting in homes. These are skylights, clerestory windows, and roof monitors or cupolas.

Horizontal or sloped skylights can cause overheating in a room because they tend to receive maximum solar gain at the hottest time of the day. The daylight contribution also peaks at midday and falls off severely in the morning and afternoon. High performance skylight designs that incorporate reflectors or glazing options are available. They can reduce the peak daylight and heat gain while increasing early and late afternoon daylight contributions. Another option is a light-pipe or solar tube that uses a high reflectance circular duct to direct daylight from a roof-mounted skylight down to a diffusing lens in the ceiling of a room.

A clerestory window is vertical glazing located high on an exterior wall. South-facing clerestories can be effectively shaded from direct sunlight by a properly designed overhang. In this design, the ceiling can be sloped to better reflect daylight into nearby rooms. Use light coloured overhangs and adjacent roof surfaces to improve the reflected component. If exterior shading is not possible, consider interior vertical baffles to better diffuse the light. A south-facing clerestory will produce higher daylight illumination than a north-facing clerestory. However, a north-facing clerestory receives only diffuse light and will not transmit solar heat gain into a home during the summer. East and west facing clerestories have the same problems as east and west windows: difficult shading and potentially high heat gains.

A roof monitor or cupola consists of a small roof section raised above the adjacent roof with vertical glazing usually located on two opposite sides. The raised roof section should be large enough to provide overhang shading for the vertical glazing. Much of the light transmitted down to the living space below is diffuse light, reflected off the walls and ceiling of the roof monitor.

Daylighting Factor.

The daylighting factor (DF) is the illuminance at a point indoors, usually on the working plane, expressed as a percentage of the illuminance outdoors. The average daylighting factor is an approximate measure for assessing daylight during the early stages in designing windows, clerestories, and roof monitors. It varies with factors such as the visible sky angle, the width and depth of the room, the net window area, the visible transmittance of the glass, and the reflectance of the surfaces inside the room. The recommended average DF for ordinary visual tasks is 1.5 - 2.5 percent. For moderately difficult tasks, the average DF ranges from 2.5 - 4.0 percent. The recommended average DF for difficult, prolonged tasks is 4.0 - 8.0 percent.

They say a picture is worth 1,000 words, so before you leave be sure to visit Von Löwen Designs to view an assortment of refreshing examples in kitchen and bath design concepts, refined palette and interior finishes, and sustainable yet chic, green remodeling ideas that may encourage and inspire your next remodel or home improvement project.