Daylighting serves as a passive lighting system, and natural light can significantly improve our mood (and treat Seasonal Affective Disorder, or SAD). Daylighting is most effective as a passive feature when it provides enough lighting for you to function around the house without needing to turn on electrical lighting during daylight hours. You should be able to move from room to room, navigate through a room or do things that do not require detailed vision without having to turn on any electric light fixtures. This includes using the bathroom, opening the refrigerator, placing dirty dishes in the dishwasher, etc. This will save energy use and, therefore, save you money.
Do not assume that all windows provide daylighting. We have walked many new construction inspections with homebuilders claiming daylighting but with only standard windows installed. Prior to occupancy, those windows are bare and allow maximum daylight to enter the space. However, in most instances, once the home is occupied, those windows will be covered with blinds or draperies for privacy. More often than not, to function within those spaces, those same occupants will not walk over to the window to open the blinds or draperies, they will just turn on a light switch. Consequently, standard windows that have a reasonable expectation of being dressed by privacy treatments do not qualify for daylighting.
Clerestory and transom windows, being high up on walls, throw light across the ceiling and provide general illumination, but are high enough on the walls that you do not feel the need to install any kind of privacy treatment, like blinds or drapes, on them. These windows are so high on the wall, anyone outside of your home would need a ladder to see into the home through them, even at night. However, if you are building next door to a two-story home, even windows high on walls may not provide privacy from your neighbors’ upstairs views. If this is the case, it’s best to save your construction budget for other energy-saving upgrades, as securing your privacy will negate the intended daylighting benefits.
In warm climates, transom or clerestory windows, because they are high on the wall, should be placed under shading devices (roof overhangs, porches or awnings) so that they are protected from direct sun and water intrusion. If you are installing a cupola or monitor or even using transom, clerestory or double-hung windows to exhaust heat, these windows provide double duty by offering daylighting and passive stack ventilation. Of course, the windows must be operable in order to serve this function.
However, you will need to install some light control materials on daylighting windows in sleeping rooms. When you’re ill, on your day off work or want to sleep late on the weekend, you don’t want to be disturbed by daylight entering the room. Interior shutters work well on bedroom windows. When you get out of bed, just open the shutters instead of turning the light on.
Skylights: Depending on your climate zone, skylights might or might not be appropriate. In hot southern climates, where the sun’s position in the sky is more directly overhead and the roof of the structure is dealing with the brunt of the heat gain in the hot summer months, skylights are usually best avoided. The exception to this is if they are ENERGY STAR-rated, and even then, applications should be limited. We know some manufacturers include tinting or integral blinds that can minimize exposure, but this might not be enough to offset heat gain through this opening. After all, by the time the heat has hit the blinds, unless the blinds are between the panes of the glass, the heat is already inside the structure.
Even in milder or northern climates, you need to remember that every penetration through the roof is a potential water leak. Skylights, like other windows, will lose their seal eventually and leak, requiring replacement. Other strategies for daylighting and passive solar can achieve better results than skylights.
For daylighting in rooms or interior hallways without a window, consider installing sun tube devices, which bring in light from the roof without bringing in the heat. They utilize a flexible tube that functions like a big fiber optic cable and is installed through the attic. Or consider installing interior windows or openings in walls to allow light into areas that do not have direct access to an exterior wall.
