As cities get hotter, builders embrace new and old ways to keep buildings cool.
Designing buildings for the local climate isn’t a new concept, but when the local climate begins to change, so must building design.
As average summertime temperatures continue to shatter records in cities across the United States, heat resiliency has emerged as a vital design consideration. Many cooling strategies, such as optimal building orientation and trees for shading, have been around for eons. These strategies, as well as more cutting-edge approaches, are having their moment in the sun as the push to keep occupants cool while saving energy grows more urgent.
Passive design uses design strategies, without relying on mechanical or electrical systems, to reduce the need for heat or air conditioning in a building.
The German-borne Passive House (Passivhaus) standard, initially slow to catch on in the United States, continues to make inroads. As of 2017, more than 1,200 projects have achieved certification from the Passive House Institute U.S. Though the standard remains largely associated with cold weather climates, airtight passive design is just as effective at keeping buildings cool in hot environments.
High-performance windows, strategic building orientation, cross ventilation and super-tight insulation, the hallmark of any Passive House project, can all be used in warm climates without sacrificing comfort.
A reflective roof is one of the most effective methods of keeping buildings cool. According to the Center for Climate and Energy Solutions, about 60 percent of urban surfaces are covered by roofs or pavement, traditionally made of dark materials that absorb about 90 percent of the sun’s energy and transfer it to the ground or buildings below. Cool roofs reflect back much more of that energy.
Highly reflective specialized coatings, tiles and shingles are the most common options. Thanks to advancements in reflective roofing products, cool roofs don’t necessarily need be white, as once was the case. While traditional dark roofs can hit temperatures of more than 150 degrees Fahrenheit in the summer, a cool roof stays 50 degrees cooler, according to the U.S. Department of Energy, allowing building occupants to crank down the AC or stay cooler in the absence of AC.
Green roofs planted with lush vegetation also help to insulate a building and decrease the reliance on cooling systems while adding aesthetic appeal.
High-performance windows and roof overhangs
High-quality windows, preferably operable, play a key role in keeping a building cool. When used properly, they promote air movement while preventing heat from leaking into a building, just as they keep the cold out.
“The weak point in the [building] envelope is the windows. But buying a good window means you don’t have leaks and you don’t have to replace the window every 10 years.”
Often imported, windows with high thermal insulation values can cause sticker shock. But as Thomas Chase, a senior project manager for Philadelphia-based nonprofit New Ecology, stressed, builders shouldn’t skimp when it comes to windows. “The weak point in the [building] envelope is the windows,” he told WHYY. “But buying a good window means you don’t have leaks and you don’t have to replace the window every 10 years.”
Wide roof overhangs are often smart choices because they shade windows.
Landscaping for shade
Lush landscaping does more than boost curb appeal. Strategically planted trees and abundant greenery can help cool buildings in even the balmiest climes. Evergreen trees, shrubs and vines in particular provide year-round relief by lowering surface and air temperatures.
Vegetation also plays a crucial role in mitigating the urban heat island effect. Heat islands run several degrees hotter than outlying areas thanks to the absorption and reflection of heat. Read more from the EPA on how to reduce the heat island effect.
Materials that boost thermal mass
In warm weather climates, bulkier is often better. As traditional building techniques such as adobe construction demonstrate, materials such as concrete and masonry excel at boosting a building’s thermal mass, its ability to absorb daytime heat and release it when the temperature drops. The use of modern building materials such as insulated concrete forms (ICFs) are an effective way to boost thermal mass while adding structural integrity.
Based in New York City, Matt Hickman writes about cities, sustainable design and the intersection between the natural world and the built environment.