Third: Windows
The conventional wisdom has long been that the lower the solar heat gain in a window, the better, Keep the outside elements from tampering with a home’s indoor temperature, the thinking goes, and let the heating and cooling systems keep the house comfortable. But when the goal is to get away from reliance on active systems for temperature regulation, that mindset has to change.
“We need to de-couple thermal performance from solar heat gain and orient glazing wisely so that it achieves solar gain in the winter but avoids driving up cooling loads in the summer,” Hindle says.
Typically, he says, a home would benefit most by having low-heat-gain windows on the building’s east, west, and north sides, with deep shading on the east and west to avoid low-angle morning and evening summer sun. On the south side, high solar-heat-gain windows will help keep the home warm in winter but must also be fitted with shading calculated to keep the sun from driving temperatures too high in summer. All windows should be high-thermal performance.
When it comes to specifying fenestration products, several of the consultants Builder spoke with warned that just relying on an Energy Star label isn’t enough. Under the new Energy Star 3 guidelines, a window needs to have a U-value of between 0.6 and 0.3, depending on where the home is built. “Passive House–quality windows are much better than that—typically around 0.14 U-value,” Hindle says. Such super-performing products will cost more, he concedes; however, their higher level of performance allows the home to run on a much smaller—and thereby less expensive—heating and cooling system.
Thanks to the arrival of high-quality European vinyl extrusion windows in the U.S. market, there are more affordable options than there have been in the past. And even if Passive House–certified windows are not in the cards, some North American window manufacturers are providing better performance.
