Much of the focus on preventing greenhouse gas emissions centers on finding renewable energy sources or using more energy-efficient heating and cooling units and appliances. Tighter building envelopes are becoming the norm in new construction and windows are part of that envelope.
The function of windows is mostly to provide natural lighting so that less energy is needed for electric lights. They also provide views and can make a small home seem larger. Inhabitants are more productive in daylit environments, and some even experience depression in darker winter months. The problem is that walls are more energy efficient when they are not broken up by openings like windows and doors. Skylights can bring in natural light, but they create holes in the roof barrier and can leak rainwater, drip condensation, or add too much heat to the interior.
There are several techniques that can be used to make a window more green:
Look for energy efficiency labels on new windows. A National Fenestration Rating Council (NFRC) label on new windows and skylights will help in comparison shopping of the most energy efficient, as will an Energy Star label. The U-factor notes how resistant to heat flow the window is. The lower the U-factor, the better insulated the home will be against heat loss. The solar heat gain coefficient (SHGC) shows what percentage of the sun’s heat will come through the window. For example an SHGC of 0.60 indicates that 60 percent of the sun’s heat will enter through the window. Visible transmittance tells how much visible light the window transmits. Higher values are important for rooms where more daylight is desired.
Window frames are usually made of wood, vinyl, steel, aluminum, and fiberglass. Fiberglass window frames are more durable, weather resistant, and do not rot, especially important in wet and humid locations. However, the key factor in window choice is how efficient it is as shown on the NFRC label.
Coatings of glazing that reflect sunlight and ultraviolet rays must be maintained to do their job well. When they peel away from sun exposure or get scratched, new coatings should be applied.
In the Greenville, South Carolina area, avoid windows on the cold north side of the house. Use double-pane, low-emissivity (low-e) windows with an SHGC of 0.60 or more to let more heat from the sun inside and a U-factor of 0.35 or less to keep heat inside in winter. Orient the house so the longest wall has most of the home’s windows and faces south. Windows on the east and west sides allow such little daylight in during the winter that they end up being a net heat loss. In summer, the sun rises in the east and sets in the west so directly that having windows on those sides overheats the house.
Clerestory windows placed high on walls are best at allowing daylight down into a room, can be opened to let more hot air escape as it rises to the ceiling in the summer, provide more privacy, and are best for hiding unwanted views.
Casement and louvered type windows open completely to allow the most air flow in warm months that do not require air-conditioning.
Windows can be positioned to induce cross-ventilation within the interior. Windows on two walls of a room will encourage a cooling cross-breeze.
Properly designed generous roof overhangs, awnings, shutters, and covered porches can shade windows from hot summer sun so less cooling energy is needed. Interior drapes. shutters and blinds can also help, but it is better to keep the heat outside in the first place.
Deciduous trees and deciduous vines on trellises can be planted outside where they will shade windows in summer, while allowing solar heat gain in winter when the leaves have fallen.
Read the article below for more information on windows and suggestions of where to buy windows in Greenville. Watch the video for how to know when to change the windows in an existing home. It may be surprising that it is typically when a window has reached its seventh year.