Basement living spaces need all the sunlight they can get. So when Washington design/build contractor Chris Landis' clients asked for an outdoor deck that wouldn't block light into the window wells of their downstairs family room, he came up with a novel solution: a deck with a translucent floor made out of Chroma load-bearing fiberglass panels from 3form. "They let light through to below, like a skylight you can walk on," he says.
Good daylighting strategies-the use of natural light to brighten up a home's interior-are increasingly in demand, especially for builders like Landis who work in mature urban and suburban neighborhoods where trees and nearby buildings often obstruct sunlight. The psychological benefits of natural light are well-documented, but daylighting also is fundamental to green building. By limiting the need to turn on lights during the day, a well-designed, daylit building is estimated to reduce lighting energy consumption by 50 percent to 80 percent, according to the USGBC.
Multitude of Options
Achieving proper natural illumination means more than simply cramming in as much glass as possible, however. It's a balancing act-part art, part science-that takes into consideration orientation and climate, window size and placement, and the color and location of interior walls.
The goal is to maximize the amount of natural light entering the house, while minimizing glare and heat gain or loss. "You want to let in just the right amount of light and nothing more," says G.Z. Brown, professor of architecture at the University of Oregon School of Architecture, Eugene, and co-author of Sun, Wind & Light: Architectural Design Strategies.
A good daylighting strategy starts with a house's layout and orientation to the sun. Southern exposures receive the most light, so a house should be sited with the long axis running east-west, which also minimizes afternoon glare. And the more narrow the building, the better. Houses one room deep with light on at least two sides allow for the most abundant and balanced natural light. Once the floor plan is designed, light can be added from the top with skylights or tubular devices, and from the side with windows and clear or translucent doors and walls.
Measuring the amount of natural light in a room takes some calculation. LEED-NC, which applies to commercial buildings and residential projects of four or more stories, calls for a minimum 2 percent glazing factor, which is the ratio of interior light to exterior light on an overcast day. It's calculated by a formula involving window area, floor area, window geometry, light transmittance, and window height (window areas above 7-1/2 feet are the most effective at dispersing daylight deep into interiors). Computer simulation also is used to measure light, with a goal of at least 25 footcandles. Although LEED practitioners have applied these standards to houses, it is balanced-rather than uniform-light that's most important in a home.
"We use Google Sketchup or a heliodon to do direct sun studies, but we aren't doing daylight calculations for single-family homes," says Dan Johnson of Arkin Tilt Architects in Berkeley, Calif. "It's more of an artistic concept-about the balance of northern and southern light and how it penetrates the house."