Windows and Sustainable Design

The evolution of windows toward sustainability.

It’s something you probably don’t think about very often – windows. They tell us a lot about a building, from its age and style to how energy efficient it is. An average home may lose 30% of its heat or air-conditioning energy through its windows, which is inexcusable considering how technology has improved since the first windows.

It wasn’t until the late 17th century that glass windows became common in homes. They were strategically placed and sized depending on geography and the sun (south-facing windows let in more light) to keep the home a comfortable temperature year round. Windows were small because glass was expensive and small meant less chance for heat to escape.

The current technology can be overwhelming and there are entire courses offered on the intricacies of the energy-efficient window. But suffice it to say that preventing air leakage, reducing condensation and increasing insulation are part of the package. Glass is stronger and thicker allowing for the use of larger slabs – entire walls can be windows. The Farnsworth House is a prime example.

Over time, windows have evolved from a mere hole in the wall to crucial components of a building’s energy efficiency rating. Here are a few of the ways that windows have changed for the better:

1. Stronger glass allows for larger windows. More natural sunlight helps regulate a building’s temperature, as in the new Virgin America’s new eco-luxe terminal at SFO.

2. Sealed window frames prevent condensation and air leakage.

3. Non-toxic gases (i.e. argon) used as filler between pieces of glass prevent loss of hot or cold air.

4. Double or triple glaze windows (storm windows) drastically improve insulation and temperature regulation.

5. Low-e glass coatings let in just the right amount of sun – because in warm climates we want the sunlight but not the heat, while in colder areas we welcome the sun’s heat and want to capture and keep it.

All of these factors improve the energy efficiency of our buildings and add credits toward LEED certification. And you thought windows were just for pretty views.

Image: dorena wm