In Green Building, Sustainability Starts on the Outside

Creating a tight building envelope is the first step to building green

By NATHAN KIPNIS

An old adage says, “It’s what’s on the inside that counts.” In green building, what’s on the outside is arguably more important. To be sustainable, a home’s exterior must be the successful resolution of a its local climate, culture, and natural resources— which is how specific building styles, also know as vernacular architecture, developed.

But today, regardless of style, a home’s exterior—namely the walls, roof, windows, and doors—should respond to its locale and be as sustainable as possible. When sustainability is top of mind, we pay better attention to how a home’s envelope functions, which results in a better built, higher quality, healthier, and more energy-efficient home.

Yet, today there’s also a new wrinkle in this equation: resiliency. Increasingly severe weather conditions are showing us that green technologies and materials don’t matter if they can’t protect a building’s interior from the pressures of storms, flooding, earthquakes, power outages, and fires. For instance, the Washington Post noted this summer that torrential rains are becoming more frequent and intense all over the U.S., leading to record rainfall, extreme flooding, and perilous infrastructure failures.

This means that when we design our residences, we have to think about the climate we will be facing now, and in the future, given the new speed of weather change. For instance, we know the already forceful rain events in our region, the Midwest, are becoming more severe every year, so we add an ice and water shield (such as the version made by Grace, an innovator in the field) to the entire expanse of roofs to prevent ice damming. That way if the roof gets severely damaged in an intense weather event, or is torn off in high winds, a residence remains watertight.

Clearly, our focus on sustainability is changing the way we build. In response, there are new, better, and more sustainable iterations of every type of product and material related to home building. Some of the newest and most promising developments include the following ideas and products:

  • Exterior Walls: Gone are the days of simply placing cement fiberboard over building wrap and plywood. Whatever materials we use for exterior walls must take into account the local climate and building codes. Rain screen systems, a type of double wall construction, are our preferred technique for exterior walls. The inner wall, or structural wall, has insulation on its exterior (in our climate we find rigid insulation board the most effective option), set on top of an air and vapor barrier skin. There is then an air gap is then between the insulation and the exterior material (be that siding, masonry or another panel type system), which remains open and vented to prevent water from getting trapped and causing mold, mildew or wood rot. Boral siding is another interesting option based on its performance, workability, and structure. It’s extremely durable and water-repellent; cuts and paints like wood; and is made out of 70 percent fly ash, which is ironically waste from coal plants, and polymers. We use it as the exposed layer in rain screens, and it can also be used for exterior trim.

 

  • Roofs: Today’s sustainable homes are unrecognizable from the residences of even a decade ago. We used to worry about how well roofs kept the water out of a residence. Now we use roofs for harvesting water, solar power generation, food production, better day lighting and natural ventilation. Still, in the winter, the average home loses a quarter of its energy as heat seeps out through the roof; in the summer, it’s the reverse as solar heat gain from radiation and convection can make homes uncomfortably warm. To combat this, attic floors should be correctly air sealed and insulated, while the attic itself should be ventilated. ‘Cool Roof’ coatings, such as shingles with an invisible coating that sunlight sees as nearly white, reflect incoming sun rays and can help reduce attic temperatures so a structure stays cooler in the summer.

 

  • Windows: The types of windows we use are key for sustainability. With 30 percent of a home’s energy dollars lost through windows, it pays to invest in double and triple-paned options. Both offer the highest performance with insulated frames. Double pane windows are standard in most climates though triple-pane windows offer the highest performance. But they have also been the most expensive and heaviest option on the market–until now. Thanks to the extremely thin glass developed for flat screen TVs, which is only 1/32 inches thick, researchers at Berkeley Lab at the University of California have developed triple- pane windows using this super-thin glass as the middle layer. The assembly delivers an R-value of R8 to R10—about twice that of the best double-pane windows sold today. It also leaves the window thin enough to fit in a double-pane window sash or frame.

 

  • Doors: There’s an energy loss cost to even a minimal crack that’s exposed under your door, and the best way to stanch it is with a tight-fitting door. While wood doors have been the gold standard, especially in luxury homes, top-quality fiberglass entry doors such as those by Threma-Tru are so good at mimicking the look and feel of wood it’s virtually impossible to tell the two materials apart. Unlike wood doors, fiberglass doors don’t warp, rot, shrink, split, crack, or swell, making them more dimensionally stable than wood. They’re also resistant to fires and pests; and extremely durable (today’s versions require no refinishing necessary, even when they face west and must endure the harsh effects of the elements). But best of all, unlike their predecessors they have textured fiberglass skins that mimic all types of wood, energy-saving insulation, myriad finish options to fit any decorative style and now they can be cut to fit any doorframe. This makes them ideal for harsh or humid climates.

Nathan Kipnis is the principal of Kipnis Architecture + Planning, an AIA Fellow, and is recognized as one of Chicago’s premier sustainable architects. For more information, please visit nexthausalliance.com

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