Published on October 23rd, 2007 | by Stephanie Evans

Daylighting for Green Homes and Spaces

Designing buildings that maximize sunlight for illumination is an efficient and effective way to lower your energy bills, reduce your carbon footprint, and protect the environment. In addition, it’s important to note that we humans are phototropic beings, meaning that we are drawn to and thrive in environments infused with natural light.

Studies show that shoppers buy more, students get better grades, and office workers are more productive when bathed in sunlight. Making winter sunlight a part of home light control systems has even healed people of seasonal depression.

Millions of people live in expansive, energy-inefficient homes that are cold and dark in the winter, hot and glaring in the summer, and have no pleasant pools of Natural Sunlight sunlight in any part of the house. These common design deficits are compensated for by fossil fuel expenditures in the form of heating, air conditioning, and electric lights. This dependence upon fossil fuels is not a condition of living comfortably in a house—it’s just a very common bad habit resulting from inefficient design and a lack of widespread awareness about healthier design principles.

Beautiful, sunlit interior spaces that gracefully and naturally reduce our impact on the planet remind us what designing with climate in mind is all about.

Passive solar building design is one very natural temperature-regulating option that makes use of the sun’s natural light as it captures and converts it into heat, storing it for later use. Passive solar design also encourages cooling, helping to keep homes warm and sunny in winter and cool and shady in summer. All functions are simply a product of good design—no input or energy from mechanical systems is needed.

Myths about Daylighting and Passive Solar Design

The newly-invented passive solar designs of the 1970’s were clumsy and inflexible. Many people thought they were downright ugly! Both residential and commercial architects and their clients became disenchanted, but that’s all changed now. The new generation of green homes using passive solar looks just like other houses. Still, myths persist about using daylighting and passive solar techniques in home design. Let’s take a look at the myths and facts to get a clearer view:

Myth: Daylighting causes overheating.

Fact: Indirect sunlight is far cooler than electric light. Properly designed daylighting screens out the sun’s heat when not needed.

Myth: Daylighting causes glare.

Fact: Glare is caused by poorly positioned home windows, such as windows on only one side of a room, windows that are not properly shaded in the summer, or windows on the "wrong" sides of the house. Good design eliminates glare.

Myth: For passive solar you need a climate with clear sunny days in the winter.

Fact: Passive solar design improves the energy efficiency of houses in virtually all climates.

Myth: There is one standard type of solar designed home.

Fact: Passive solar design means designing with climate in mind. Every climate, every latitude, will have different design criteria.

Passive solar homes are designed to flow with the seasons. The classic passive solar structure has a long east/west axis with most of its windows on the south side. In the winter (in the northern hemisphere) the arc of the sun is low in the southern sky and sunlight shines in, warming and lighting the house. In the summer, when the sun’s arc is almost directly overhead, little or no sunlight enters the house directly and the house stays cool.

Passive solar designs also utilize heat from thermal mass—often an insulated concrete slab or sometimes adobe, brick, or stone—that soaks up the heat of the sunlight and gives it back when it gets cold. Incorporating the daylighting concepts of passive solar into any home design reduces energy costs and brings pleasant natural light streaming in. For a concise guide to the elements of passive solar design visit the U.S. Department of Energy’s Five Elements of Passive Solar Home Design.

Orienting for Natural Light

Window orientation, placement, and size are all critical in good daylighting design. The size of your windows is best assessed as a calculation of the total square footage of glazing in each direction. Placement refers to where in the wall the window is. For example, high windows under eaves will let in less direct light. To optimize the daylighting effect, most of your home’s windows should be oriented toward the south side to let in maximum winter sun and minimum summer sun. An overhang or eaves calculated to shade out the direct summer sun at your latitude is essential.

East-facing and, even more, west-facing windows will let in too much sunlight in the summer unless they are carefully shaded and they don’t offer nearly as much winter sunlight compared to south windows. Windows facing these directions should be used judiciously. East-facing windows are particularly pleasant in rooms used in the morning, such as bedrooms, bathrooms, and kitchens.

North-facing windows let in a cool, indirect light—the sun will never shine in directly—but they also lose a lot of heat in the winter and they are thus usually minimized in passive solar design.

Retrofitting

It all sounds great, but sometimes razing your present house to the ground and building a passive solar one in its place just isn’t an option! Let’s review the options that leave your home still standing while helping your current natural lighting features adapt to the seasons, all without fossil fuel inputs.

Shading retrofits
South- and west-oriented windows in particular need shading in the summer to reduce glare and heat build-up, which saves on the electricity used for air conditioning. Planting deciduous trees that will lose their leaves in winter (allowing in the winter sun) is, environmentally speaking, the best choice—but not always possible. It also can take some time to have an effect. A trellis of annual vines provides an interim solution while waiting for your trees to grow.

Another option is to add an awning that can be retracted in winter. Window awnings installed on west-facing windows can reduce solar heat gain in summer by up to 77%. Modern awnings are made of waterproof materials, such as dacron, vinyl, and acrylic, that resist mildew and fading. For more about awnings, visit the Deparment of Energy’s review of Window Awnings.

Other options include shades such as interior blinds, although it is always more efficient to stop sun outside of your windows—before the heat gets in. Vertical or horizontal blinds do come in natural materials, such as bamboo or wood. Louvred blinds offer a lot of shading flexibility. For more information, visit the Department of Energy’s review of Interior Blinds.

Don’t forget window shades. Exterior shades are especially good for creating shade for porches and verandas and they can be adapted for most windows. Woven materials, usually synthetic, allow some viewing while screening out a lot of sun and heat. For more about shades, visit the Department of Energy’s Shades page.

Lighting Retrofits
Skylights and solar tubes are options that help to bring natural solar light into dark interiors. Old-style skylights have a deserved reputation for letting in heat in the summer, letting it out in winter, and leaking any time it rains! The new prefabricated tubular skylights address these problems. They are typically composed of three parts:

a clear acrylic rooftop dome and flashing
a flexible "light pipe" lined with reflective material that can be almost any length and can bend around obstructions
an interior light diffuser that eliminates glare

In the ceiling, tubular skylights appear much like an overhead light fixture. Because they are smaller than traditional skylights, they are much easier to install in almost any roof and no expensive reframing is needed. Visit GetWithGreen’s review of Solar Tubes.

A south-facing clerestory (a row of small windows near the ceiling) provides additional sunlight without glare. Clerestories are often part of a green home light control system.

Promising Technology—Hybrid Solar Lighting

Hybrid solar lighting is a technology developed by the Department of Energy’s Oak Ridge Lab in Tennessee. The technology, used to channel sunlight into buildings by means of optical fibers, has potential for great energy savings, especially for lighting commercial buildings. One company, Sunlight Direct, is already marketing it to industry. Rather than converting sunlight to electricity and then back into light (as do lighting systems powered by photovoltaic cells), hybrid solar lighting uses a rooftop collector to funnel light directly into buildings via optical fibers. This method is both extremely efficient and provides full-spectrum, cool, natural light at peak usage periods. On dark days the light output is boosted by conventional electricity (the ‘hybrid’ part).

Building development that illuminates, heats, and cools structures and homes through good design, rather than by non-renewable energy inputs, is the wave of the future. Tapping the power of solar energy doesn’t have to be expensive and complicated. Beautiful, sunlit interior spaces that gracefully and naturally reduce our impact on the planet remind us what designing with climate in mind is all about.