Next-generation building materials can keep South Florida homes cool and cut energy costs
Reflective roof coatings, permeable pavements, heat-proof windows that bounce away the sun’s energy, super efficient air conditioning units that burn less electricity to tame increasing temperatures: A host of new materials and equipment can lower buildings’ cooling costs and reduce their carbon emissions — which account for about a quarter of global greenhouse gasses, according to the International Energy Administration.
“If you replace 10-year-old technology with new technology that meets the energy code, then you’re definitely doing better,” said Steve Samenski, director of building performance for The Spinnaker Group, a South Florida-based green building consulting firm. “A homeowner can probably expect a 10% to 20% improvement if all else is the same.”
All of this next-generation stuff is available now for new home and building construction and along with being climate friendly, will save owners money in the long run. But they’re often not the first option for builders and developers, who often are more concerned about profit from an initial sale. But efficiency also can be a selling point and with climate change a growing concern for customers — particularly in South Florida — designers and contractors are increasingly open to making upgrades.
In recent years, in fact, some South Florida architects have tapped building techniques from the past to design buildings from the ground up to take advantage of breezes, shade and advanced materials to withstand the summer heat. But you don’t need to rebuild your entire home to improve its energy efficiency. These materials are already on the market and can be used to retrofit existing buildings and lower their energy costs.
Roofs bear the brunt of the sun’s heat throughout the day. A conventional roof can heat up to 150 degrees on a sunny summer afternoon, according to the U.S. Department of Energy. A poorly insulated roof will transmit that heat into the rooms below.
But so-called “cool roofs” are designed to reflect the sun’s energy before it can be absorbed into the building. A roof made from reflective materials can stay as much as 50 degrees cooler than a conventional roof at the peak of summer, according to the Energy Department.
Turning a conventional roof into a cool roof can be as simple as painting it white. But for extra cooling power, building owners can apply reflective coatings which bounce away more of the sun’s rays and typically last longer without chipping or peeling. Manufacturers even sell cool shingles in a variety of colors that can also bounce away heat thanks to special, reflective granules embedded in the material.
A cool roof treated this way can reduce the energy needed for air conditioning by up to 15 percent for a single story building, according to the non-profit Environmental and Energy Study Institute. For a typical Florida home spending $136 a month on electricity, that would mean saving about $147 a year on cooling.
The price of cool roof treatments varies, but at the high end, they might cost up to 20 cents more per square foot than standard options, according to the EPA. For the average U.S. residential roof, which measures about 1,700 square feet according to census figures, that means a cool roof might cost up to $340 extra. So it’ll pay for itself in a few years.
Much like cool roofs made from reflective materials, “green roofs” covered in plants can stay as much as 40 degrees cooler than conventional roofs on sunny summer days, according to the U.S. Environmental Protection Agency (EPA). They typically cost even more upfront and require you to maintain the plants — but they create similar energy savings and have the added benefit of beautifying the roof.
Solar panels can also cool down roofs by capturing the sun’s energy and turning it into electricity before it can reach a building. Solar panels can lower the temperature of the ceiling in the rooms below by 5 degrees Fahrenheit, according to a 2011 study from researchers at the University of California, San Diego and NASA.
High efficiency windows
The biggest gaps in a building’s heat armor are typically its windows, which allow sunlight to pass directly into the interior and can also let warm air leak in from outside.
There are a lot of factors that influence your windows’ energy efficiency: the material and fit of your window frames, how many layers of glass your window has, whether or not you treat the glass with thermal treatments, whether or not you fill the space between window panes with insulating gasses and so on.
All these factors, plus the size and style of the window, mean you might pay anywhere from $280 to $1,500 each for a double-pane, insulated window, according to Architectural Digest. But there are federal tax credits that can help bring down the cost: Homeowners who install windows rated “most efficient” by Energy Star can get a tax credit for 30% of the cost up to $600 under the Inflation Reduction Act.
One way to bring down the temperature is with low-emissivity (low-e) coatings, which reflect the invisible infrared light that carries much of the sun’s heat while allowing visible light to pass through normally. Low-e windows typically cost 10 to 15 percent more than regular windows, according to the Energy Department, but reduce the amount of heat that passes through a window by 30 to 50 percent.
Low-e windows can be so effective at reflecting heat, however, that they’ve been known to melt nearby plastic yard furniture or neighbors’ vinyl house siding on summer days.
Cool pavements — asphalt and concrete made with reflective material or coatings, for instance — can lower the temperature in paved areas outside of a building, which may make a difference in how comfortable it feels to stand outside on a hot afternoon.
Much like roofs, pavements can heat up to 150 degrees Fahrenheit on sunny summer days, according to the EPA. They then radiate that heat back into the air, warming cities as part of the “urban heat island” effect. Miami has one of the worst urban heat island effects of all major U.S. cities, according to a recent report from the non-profit research group Climate Central.
MIT researchers tested cool pavements in Boston and Phoenix and wrote in a 2021 study that they could lower air temperatures by 3 degrees in Boston and 3.7 degrees in Phoenix if they were used throughout the city.
In a similar 2021 pilot program, the city of Phoenix found that cool pavements were 10.5 to 12 degrees cooler than traditional pavements in the afternoon.
However, cool pavements reflected some of that heat back onto pedestrians, meaning that the “human experience” of someone walking across cool pavement in the afternoon was “similar to walking on a typical concrete sidewalk,” according to the city.
A/C Finally, a more efficient air conditioner can directly lower the amount of electricity and money a building spends on cooling.
A/C manufacturers have been steadily improving their machines’ efficiency since the 1990s to keep up with federal regulations. If you’ve replaced an air conditioner in recent years, you’ve probably upgraded its efficiency and lowered your energy bill.
Replacing a decade-old air conditioner at the minimum efficiency level with a new system at today’s minimum would lower your electricity spending on air conditioning by about 13%, or roughly $150 a year for a 2,000 square foot house, according to utility FPL.
The urgency of energy efficiency
Efficiency improvements can make a big difference for the future occupants of the building, according to Sonia Chao, associate dean of research at the University of Miami School of Architecture. “You can think of building materials almost like clothing,” she said. “If you’re standing in the sun dressed in a white, light cotton shirt versus a dark wool, how quickly would you feel uncomfortable in dark wool?”
And, as scientists expect global temperatures to continue to rise, the need to cool down buildings is becoming all the more urgent. “We’re not taking seriously the changes we need to make as a building profession and a design profession,” said Samenski. “The targets out there for decarbonization are really dramatic and business as usual is not going to get us there.”
This climate report is funded by Florida International University and the David and Christina Martin Family Foundation in partnership with Journalism Funding Partners. The Miami Herald retains editorial control of all content.
This story was produced in partnership with the Florida Climate Reporting Network, a multi-newsroom initiative founded by the Miami Herald, the South Florida Sun Sentinel, The Palm Beach Post, the Orlando Sentinel, WLRN Public Media and the Tampa Bay Times.