In our prior discussion, we looked at exterior walls as a means to provide natural daylight in buildings, but roofs are also a superior source to bring in daylight.

Building Shape: Low-rise and one-story structures are less restricted by building shape than multi-story buildings since single-story interior spaces can all be designed to have access to the roof for daylighting. It is also popular to use a central atrium in multi-story buildings that provides interior spaces access to a common space that is daylit from the roof. Either way, the key is to coordinate the location of roof daylighting openings with the uses of the interior spaces to provide even light distribution where it can serve as an optimum source.

Roof Daylighting: Daylight can be brought into a building through the roof by using well-known techniques such as skylights, roof monitors, and clerestories. It is also possible to incorporate domed, cylindrical “light tubes” that are specifically designed to maximize the daylight received at any angle and direct it down into the building in strategic locations. The advantages of any of these rooftop daylighting techniques include direct access to the entire sky, a more consistent distribution of daylight, easier glare control, and the ability to daylight interior spaces and large floor areas regardless of building shape. When designing for roof daylighting, the Architecture 2030 Palette (www.2030palette.org) recommends the glazing area should be a minimum of 10 – 20 percent of the floor area to be daylit, although that can vary based on the specific technique.

In the case of metal buildings with metal roofing systems, the incorporation of any type of roof opening needs to be carefully addressed for proper flashing, weatherproofing, and longevity. The metal building industry has an array of envelope solutions and procedures in place to accommodate the use of daylighting systems on a metal roof. These systems incorporate some emerging technologies like prismatic embossed skylights for enhanced illumination. Speak with your manufacturer for specific product offerings in this regard.

Daylight Control: Anytime bright daylight is brought into a comparatively darker building, there is a need to control the amount and quality of that light to prevent uncomfortable glare or unwanted lighting contrasts. For exterior walls, some form of louver, blind, or baffle is typically employed, either on the interior or exterior of the building, in order to allow people to redirect or filter sunlight coming into a space. In roof systems, direct sunlight can be filtered and distributed over a space by using translucent glazing material, baffles, and reflectors, or by bouncing sunlight high off a light-colored interior surface or wall. Light tubes have addressed this by incorporating filters that diffuse and alter the quality of the light, filtering it down to the level of the average electrical light fixture.

Energy Savings: In order to take full advantage of the energy savings natural daylight can provide, the usage of electrical lights would need to be reduced during daylight hours. While it may make sense in some situations to use typical hand-operated light switches, in most cases it is more efficient to use automatic sensors that connect to controls that can dim or turn off the electric lights. Dimming is often preferred and requires a lighting system that is equipped for such, for example, LED lights or dimmable fluorescent fixtures. Many energy codes recognize the potential energy savings from using daylight and identify “daylight zones” in a building that requires such automatic lighting controls.

More Information: The metal building industry has embraced the benefits of natural daylight with the development of adaptable materials and integrated metal envelope and roof solutions. You can find out more in a free white paper titled “Shining Light on Daylighting with Metal Roofs” at http://www.mbci.com/daylighting/.

Before the common availability of electrical lighting, natural daylight was the only real option in buildings. Many solutions, both simple and sophisticated, have evolved from the quest of bringing natural sunlight into the building envelope. Current building trends have seen a renewed interest in reviving the techniques of using natural daylight as a replacement for electrical lighting to create more appealing spaces that are also less costly to operate. Daylight can enter through the building walls, the roof, or both. In this discussion, we will focus on some basic techniques of using walls to provide daylighting.

Design Tools: Many resources and computer modeling tools address daylighting in considerable depth. One of the most concise and useful resources is from the not-for-profit organization Architecture 2030, whose mission is to reduce energy usage in buildings. The 2030 Palette provides not only “rule-of-thumb” guidelines but also examples of design principles put into practice, plus detailed informational resources (www.2030palette.org). Using such information for metal buildings relies on the same fundamental daylighting principles that apply to any other building; however, there are a few specific things to keep in mind with metal building construction.

Building Shape: A multi-story building that is shaped to maximize access to daylight typically has a narrow footprint. Since it is difficult to direct sunlight deeply into a building from an exterior wall, a narrow shape allows more of the spaces to have access to the light source on an exterior wall. Building footprints can be elongated, curved, or be made up of multiple smaller shapes to achieve the best access to daylight. Using high ceilings and high windows allows daylight to penetrate deeper into buildings compared to those with low ceilings and lower windows. If buildings are elongated in the east-west direction, the longer north and south sides will be exposed to different types of direct and indirect daylighting. If they are elongated in the north-south direction, then the longer sides will receive direct sunlight at different times of the day and indirect sunlight at others.

Exterior Wall Daylighting: The 2030 Palette suggests that acceptable interior daylight levels for task lighting can be achieved at a depth of 1.5 to 2 times the height of a glazed opening (i.e., window, panels, etc.). In most cases, that equates to between 10 to 20 feet inside the building from the wall, although a tall metal building with upper-level windows or light transmitting panels will have an advantage. An interior light shelf added to a glazed opening will reflect daylight deeper into a space, and can increase the useful daylighting depth to 2.5 times the height of the glazed opening.

The total amount of glazing area along an exterior wall is also important in terms of effectiveness. The general rule of thumb in this case is to provide glazing in 10 -15 percent of a wall area at a minimum, for basic daylighting levels, with 15 – 25 percent preferred for more-adequate daylighting levels. (Note that most energy codes are based on a maximum of 30 – 40 percent total glazed openings in walls.) Where possible, daylighting spaces from multiple sides can provide lighting that is more evenly distributed while producing less glare in the space. When it is not possible to provide daylighting from multiple sides, utilizing lighter colors for side walls and ceilings and incorporating high ceilings and windows with light shelves will help.

Conclusion: Incorporating these principles of exterior wall daylighting into the design of metal buildings has been embraced by many metal building manufacturers. By working directly with a manufacturer during the building design process, the benefits of daylighting can be achieved using conventional metal building construction techniques that are cost-effective and consistent with project time schedules.