Sustainable Design: Eco-friendly Windows

A kitchen with island, white cabinets and large windows
  • 2-50 hours
  • Advanced
  • 500-30,000

Windows play a key role in the sustainable design of any house. They are the objects through which most energy and light pass in and out of a building, and for this reason when properly designed, they can not only significantly reduce the heating and cooling expenses of a household, but also contribute to the preservation of the environment. There are a few things you should consider in order to ensure the optimal energy performance of your windows.

Window Energy Rates

outside of a home with large windows

There are currently many types of windows to choose from, and this can naturally lead to much confusion. To clarify things, the British Fenestration Ratings Council has introduced a system of ratings, which indicate the energy efficiency of a window type. These ratings vary from A to G, where A signifies the best performance, and every window is graded with a letter before its introduction to the market.

Several window characteristics are taken into account to estimate its rating.

U-Value indicates the heat loss through the window (the lower the value, the greater the energy efficiency);

Solar Factor shows the capacity of the window to absorb heat from sunlight. It is measured with either zero or one, where one signifies better capacity for heat gain.

Air Leakage measures the amount of air that passes through the window when it is closed.

Depending on the frame and glass from which it is built, a window will have different values for these characteristics and, thus, a different efficiency rating.

Window Frames

Window sustainability depends to a great extent on the type of material from which the frame is made. Wooden frames, for example, are quite energy-efficient, but they must be maintained (scraped, cleaned and repainted) on a regular basis to protect them from the elements. Moreover, they tend to be more expensive than other frame types.

Fiberglass window frames preserve energy just as well as the wooden ones. Unlike them, they do not need much maintenance, yet may be just as taxing on the customer’s pocket.

Aluminum frames are cheap, but conduct heat rather easily and have, therefore, poorer energy efficiency.

PVC or vinyl frames are the last common type of frame. They are reasonably priced, have good energy conservation properties and are not very expensive. However, to ensure optimal thermal performance, you may have to insulate them.

Window Glazing

man glazing a window

The innovation of window glazing has immensely improved the energy efficiency of windows. Window glazing is basically two or three panes of glass separated by spaces of vacuum, which serve to reduce energy transfer, keeping heat inside the room during the winter months and obstructing its entrance in the summer. Recent formats of window glazing can also serve as good noise insulators.

Often a coating of metal or metallic oxide, commonly known as low-emissivity or low-e coating, is applied to the window panes in order to provide even better energy performance.

Тhe spacers of the window glazing, i.e. the pieces that separate the panes inside the window frame, are made from low-conductivity materials (fiberglass, vinyl, silicone foam, etc.) to ensure optimal window sealing and heat conservation.