# data[].attributes.attachment_link.readable_text
Purdue Professor Xiulin Ruan and his team have developed the world's "whitest" white paint (Credit: Joseph Peoples/Purdue University)

Given that white was one of the first colors used in art in the 15th century, one would think that there is little room left to improve its "whiteness." It turns out that is far from the case. A team of researchers led by Xiulin Ruan, a professor of mechanical engineering at Indiana's Purdue University, recently revealed an "ultra-white" paint that they believe could even help combat climate change.

The scientists, who spent six years creating the world's "whitest white" paint, assert that the options currently available make surfaces warmer rather than cooler. That's because they only reflect 80 to 90 percent of the sunlight and cannot make the exterior cooler than the surrounding temperature. The newly-revealed ultra-white paint not only reflects 98.1 percent of sunlight, but also prevents surface infrared heat from being absorbed.

"We think of 90% to 98% as not very different, but we need to think about the absorption of the sunlight," Dr. Ruan says. "Our paint absorbs 1.9% of sunlight, but those commercial paints, even with reflectants, absorb 10% of the sunlight-five times as much as our paint absorbs. They look white, they are pretty white, but they aren't white enough-they're not able to cool beyond the ambient temperature."

Purdue researchers Xiulin Ruan (left) and Joseph Peoples use an infrared camera to compare the cooling performance of white paint samples on a rooftop ( Credit:Jared Pike/Purdue University)

The ultra white paint's incredible cooling ability can be attributed to the use of a high concentration of barium sulfate, in lieu of the commonly-used titanium dioxide as a pigment. The chemical compound, which can be found in cosmetics and photo paper, does not absorb UV light. The researchers also varied the size of the chemical compound's particles to allow for maximum diffusion of sunlight.

"A high concentration of particles that are also different sizes gives the paint the broadest spectral scattering, which contributes to the highest reflectance," said Purdue Ph.D. student and study participant Joseph Peoples.

Outdoor tests of the newly-formulated paint indicated it could keep surfaces 8 degrees Fahrenheit cooler than the ambient temperature under the strong noon sunlight and as much as 19 degrees Fahrenheit cooler at night. Given that the paint is as efficient in the winter - lowering surface temperatures by 18 degrees Fahrenheit when outdoor temperatures were below 43 degrees Fahrenheit - it would be most effective in areas with year-round hot weather.

"We did a very rough calculation," Dr. Ruan told the BBC. "And we estimate we would only need to paint 1 percent of the Earth's surface with this paint - perhaps an area where no people live that is covered in rocks - and that could help fight the climate change trend."

An infrared image showing how a sample of the 'whitest paint' (the dark purple square in the middle) cools the board below ambient temperature (Credit: Joseph Peoples/Purdue University)

However, Hashem Akbari, professor of building, civil, and environmental engineering at Concordia University, believes the paint's real benefits can only be ascertained after being in use for a few years. "Soot and dust tend to decrease the reflectivity of the surface," Akbari told Gizmodo.com. "If they start with super-duper 95% reflectivity, the pollutants from the air, the droplets, soot could collect on the surface, and they decrease the reflectants."

Meanwhile, Andrew Parnell, who works on sustainable coatings at the University of Sheffield, UK, is concerned that the carbon dioxide emitted by the mining of barium sulfate may offset the lower energy outlay caused by the ultra white paint. He instead believes that green or living roofs, which are covered with vegetation, may be a more practical and effective solution to combat global warming.

The Purdue researchers, who published their study in thejournal ACS Applied Materials & Interfaces on April 15, 2021, are undeterred by the skeptics. The team is not only working with manufacturers to bring the ultra white paint to market, but also developing other "energy-efficient" colors. Dr. Ruan has even hinted at creating a dynamic paint that can reflect heat in the summer and absorb it in the winter!

Resources:eurakaalert.org, gizmodo.com, bbc.com

# data[].attributes.attachment_link.title
Can The World's Whitest White Paint Help Reduce Global Warming?

# data[].attributes.attachment_link.description
Given that white was one of the first colors used in art in the 15th century, one would think that there is little room left to improve its "whiteness." It turns out that is far from the case.

# data[].attributes.attachment_link.title
Keeping roofs cooler to cut energy costs

# data[].attributes.attachment_link.description
Cool it! A cheap paint-on coating for roofing shingles could help reduce a home’s heating bills and might even trim urban ozone levels, a teen shows.

# data[].attributes.attachment_link.readable_text
In the summer of 2019, a blistering heat wave swept across Europe. France was particularly hard hit. In some places, the temperature hit 46° Celsius (115° Fahrenheit). More than 1,400 people died, some in their own homes - buildings that were never designed to withstand the intense heat that has arrived with climate change.

A year earlier, a heat wave in Montreal, Canada killed 66 people. Eight in every 10 of them died in their homes. Meanwhile in the United States, more than 600 people die from extreme heat every year. Like those in France and Montreal, many of them die in homes built for cooler climates.

All across the world, climate change is delivering on its promise to bring hotter, longer summers. While heat kills everywhere, buildings in northern temperate regions are particularly bad at keeping the people inside cool.

Instead, buildings rely on air conditioning, which makes outdoor temperatures even hotter. That's because air conditioning works by taking heat from inside and blowing it outside. This increases temperatures for people outdoors and for those who live or work in buildings without air conditioning.

Plus, the fossil fuels used to make the electricity that powers air conditioners produce greenhouse gases, making climate change worse.

Air conditioning, in other words, is not a sustainable solution. And there's no easy answer for how to keep people cool in the increasingly worse heat waves brought about by climate change. But there's plenty of ideas for how people can stay cool. The first step: Look to the South.

Paint your roof

People living in places such as northern Europe, Canada and the United States could learn a thing or two from countries in the tropics, says Kurt Shickman. He is executive director of Global Cool Cities Alliance, based in Washington, D.C. This group helps cities around the world design cooler buildings and outdoor spaces.

Reflective roofs and walls is one most effective and least costly ways to cool a building, notes Shickman. It can be as simple as painting them a very light color such as white, to reflect sunlight.

"In India, people repaint their roofs every year, and it's super cheap," he says. "When you do that across a line of buildings, you can have a pretty significant reduction in temperature. We're talking 2.8 to 5.5 degrees Celsius [5 to 10 degrees Fahrenheit cooler]."

By contrast, roofs and walls in northern cities are often darkly colored. This absorbs heat and transfers it to the building.

A small experiment can help you feel the effect for yourself, says Shickman. Put a piece of white paper and a piece of black paper in the sun on a hot day. The same amount of sunlight is hitting each. But the black piece will absorb the sun's radiation while the white piece reflects it. After a few minutes, the black one will be warmer to the touch.

You don't necessarily need to paint your roof white to get this effect. In places where roofs are traditionally dark, you can keep the color. That's because researchers have developed new reflective roofing materials, says Shickman.

Scientists at Lawrence Berkeley National Laboratory in California and Oak Ridge National Laboratory in Tennessee, for example, have developed reflective asphalt shingle, metal and tile roofing materials. Even though they are dark-colored - green, brown, blue, red - they still keep their cool.

How? It starts with understanding that sunshine is made up of three different wavelengths of light: ultraviolet, visible and near- infrared (In-fruh-RED). The human eye only needs sees visible wavelengths. About half of the sun's energy is invisible near-infrared light.

Traditional dark roofs absorb all three types of light. But those made from the new roofing materials reflect the near-infrared light. With about half the sun's light bouncing back into space, these roofs don't heat up nearly as much as those covered with traditional roofing materials.

What about when winter comes to northern cities? After all, despite rising temperatures, winter can still be cold in the North. Is it a good idea to have a reflective roof when you want to keep your home warm?

Yes, say scientists at Lawrence Berkeley National Laboratory. The extra energy it takes to heat a building with a reflective roof in the winter is less than the energy it takes to cool the same building in the summer, they found. Plus, if a roof is covered with snow, its color doesn't matter because its surface will be white.

Green your building with plants

Another lesson from the tropics comes from the southeast Asian city-state of Singapore. In 2009, its government decided it would pay for up to half the cost of roof and wall gardens. (Wall gardens consist of plants in some kind of container - a pot or a narrow box - attached to a wall.) The move was motivated in part by the fact that plants absorb carbon dioxide, a greenhouse gas.

Greenhouse gases trap energy from the sun and cause temperatures to rise. Burning fuel to drive cars, heat homes and run factories releases even more greenhouse gases into the air. This leads to rising average temperatures across the globe.

Since launching, Singapore's program has helped to green more than 110 buildings. One of them is the Oasia Hotel Downtown. Architect Hong Wei Phua designed the high-rise building with four garden terraces - on the 6th, 12th and 21st stories, plus the roof. Because the terraces are open on all sides, they allow air to flow across them naturally. This helps keep the building cool and reduces its need for air conditioning.

The building also can support vines that grow all the way up its sides. "The secret is that every story has a ring of planters," Hong Wei says. "All the plants need to do is climb one story, not from the ground all the way up to the 27th floor."

The vines are accessible on every story as well. Behind the ring of planters, there is an inner "catwalk" ring that gardeners can use for inspecting and caring for the plants.

Of course, Singapore has a tropical climate that supports year-round greenery. But even in northern climates, where plants go dormant each winter, green roofs and walls are possible, says Liat Margolis. As a landscape architect, she studies the environmental impact of green roofs and walls. Margolis works at the University of Toronto in Canada.

How plants cool

Rooftop plants do not directly cool a building. Instead, as they transpire water during the heat of the day they cool the surrounding air. Margolis says it's "just like how our bodies sweat through pores in our skin."

When the sun shines, plants open their stomata (Stow-MAH-tuh). These are tiny openings on a leaf's surface. Water passes through them into the air. As that water turns to vapor, it cools the air.

No one knows how many green roofs it might take to cool an entire city. There are very few studies at that scale. But Margolis and her team do know which plants, soils and irrigation systems offer the most effective cooling in Toronto. Sedum (SEED-uhm) plants in well-watered organic soil are champion coolers. Sedum is a low-growing, fleshy plant with small overlapping leaves and yellow, white or pink flowers.

Her team experimented with different test beds of plants on the fifth floor of a university building. Over the course of two growing seasons, the air just above the sedum plants in organic, watered soil was 2 degrees Celsius (3.6 degrees Fahrenheit) cooler than the air above unwatered grasses and wildflowers growing in inorganic soil.

GRIT Lab, University of Toronto

One reason is that the sedum plants tend to spread and cover the entire surface of the test bed. Rich organic soil and regular watering makes the plants grow even thicker.

Grasses and wildflowers don't spread as much. When grown in poor soil and watered only by rain, they will thin out. During dry months, they may disappear altogether.

Margolis showed the cooling effect of plants comes from how much of an area they cover, not their biomass (BYE-oh-mass). Biomass is the quantity (mass) of living matter.

For wall-growing plants, species matter, too. Grape vines and Virginia creeper vines are among the best, Margolis finds. That's because when they go dormant in the winter, their stems don't wither away. Later, when spring comes, the vines don't have to take time to grow stems and then leaves. Instead, their leaves quickly cover walls and begin the work of transpiration.

Using the same fifth-floor rooftop, Margolis and her team grew the vines up sections of a one-story wall. They compared the air temperature just above the vines' surface to that just above the bare wall. Vines made the air 3 degrees Celsius (5.4 degrees Fahrenheit) cooler.

But planting vegetation on buildings and keeping it healthy isn't cheap, Margolis points out. And it can take a lot of work. There may be simpler strategies.

In with the old, out with the new

Sometimes the secret to a cooler home can be as simple as reminding ourselves of architectural strategies from the days before air conditioning, says Megan Davies Wykes. An engineer at the University of Cambridge in England, her work focuses on the field of fluid dynamics. That's the study of liquids and gases in motion.

Davies Wykes is particularly interested in how air (a collection of gases) moves through a room. She experiments with various models to get air to flow naturally across a room. She wants to help architects design homes, schools and workplaces with cooling ventilation as one way to lower a need for air conditioning.

There are two ways to do this, she says. The first relies on wind. As winds blow, they push air against a building; this creates an area of high pressure. The opposite side of the building is sheltered from the wind. Here, the air pressure is lower.

Fluids and gases, including air, naturally move from high-pressure areas to low pressure ones, notes Davies Wykes. If the wind is blowing and there are open windows on opposite sides of a room, air will move from the high- to the low-pressure sides. This creates a cooling breeze as that air passes through the room.

Many homes built before air conditioning have rooms or hallways with windows directly across from each other. As long as no big objects block the way, this cross-ventilation allows the breeze to flow through rooms.

"Windows on two adjacent walls works, too, but not as well as windows directly across from each other," Davies Wykes explains.

But what if there is no wind? Anyone who has tried to cool down on a summer night by opening a window will know that without wind, there is no breeze. That's when you can turn to the second way to create ventilation. This involves taking advantage of the temperature difference between indoor and outdoor air. While the breeze is not as strong as one driven by wind, it can still make a difference, says Davies Wykes.

Warm air rises and creates a vacuum. This in turn pulls cooler air up, creating a breeze. But inside a room, warm air rises to the ceiling and gets stuck. There must be an opening high up on the wall or the ceiling for warm air to escape and create the vacuum needed to pull air in and set up a breeze. A high window or skylight is ideal. You also need a window lower down on the wall to pull in that cooler air from outdoors.

Davies Wykes says old-fashioned double-hung windows are a good way to generate this kind of breeze. These are windows with one sash (glass-filled frame) that slides up and another that slides down. This allows you to create an opening higher up on the wall, and another lower down.

"We used these techniques for centuries, but we've forgotten about them," she says.

Yet even if your building is poorly designed or has no vegetation, there are ways to keep cool during a heat wave. Shickman, of the Global Cool Cities Alliance, suggests closing blinds or curtains during the day to block out the warming sunlight. Make sure, too, that they are a light color on the side facing out so that they reflect sunlight.

Computers, TVs and other electronics generate a lot of heat when sitting idle or even when turned off. So unplug them when not in use, says Shickman. And when possible, don't use your stove or oven - eat a cold meal instead.

If you've done all these things and your home is still uncomfortably hot, don't beat yourself up about having to use your air conditioner. Remember, heat can kill.

"I live in Washington, D.C., and try not to run my air conditioning much," says Shickman. "But I'm a big, bearded guy with small kids, so sometimes I just have to."

Power Words
More About Power Words

air pressure: The force exerted by the weight of air molecules.

average: (in science) A term for the arithmetic mean, which is the sum of a group of numbers that is then divided by the size of the group.

biomass: Matter that contains carbon and can be used as a fuel, especially in a power station for the generation of electricity. Plants are a kind of biomass.

carbon dioxide: (or CO ₂) A colorless, odorless gas produced by all animals when the oxygen they inhale reacts with the carbon-rich foods that they've eaten. Carbon dioxide also is released when organic matter burns (including fossil fuels like oil or gas). Carbon dioxide acts as a greenhouse gas, trapping heat in Earth's atmosphere.

climate: The weather conditions that typically exist in one area, in general, or over a long period.

climate change: Long-term, significant change in the climate of Earth. It can happen naturally or in response to human activities, including the burning of fossil fuels and clearing of forests.

dormant: Inactive to the point where normal body functions are suspended or slowed down.

dynamic: An adjective that signifies something is active, changing or moving. (noun) The change or range of variability seen or measured within something.

electricity: A flow of charge, usually from the movement of negatively charged particles, called electrons.

electronics: Devices that are powered by electricity but whose properties are controlled by the semiconductors or other circuitry that channel or gate the movement of electric charges.

engineer: A person who uses science to solve problems. As a verb, to engineer means to design a device, material or process that will solve some problem or unmet need. (v.) To perform these tasks, or the name for a person who performs such tasks.

fossil fuel: Any fuel - such as coal, petroleum (crude oil) or natural gas - that has developed within the Earth over millions of years from the decayed remains of bacteria, plants or animals.

glass: A hard, brittle substance made from silica, a mineral found in sand. Glass usually is transparent and fairly inert (chemically nonreactive).

greenhouse gas: A gas that contributes to the greenhouse effect by absorbing heat. Carbon dioxide is one example of a greenhouse gas.

inorganic: An adjective for some chemical substance that does not contain carbon from living organisms.

irrigation: An engineered supply of water to land or crops to help growth.

metal: Something that conducts electricity well, tends to be shiny (reflective) and malleable (meaning it can be reshaped with heat and not too much force or pressure).

model: A simulation of a real-world event (usually using a computer) that has been developed to predict one or more likely outcomes. Or an individual that is meant to display how something would work in or look on others.

organic: (in chemistry) An adjective that indicates something is carbon-containing; also a term that relates to the basic chemicals that make up living organisms. (in agriculture) Farm products grown without the use of non-natural and potentially toxic chemicals, such as pesticides.

pore: A tiny hole in a surface. On the skin, substances such as oil, water and sweat pass through these openings.

pressure: Force applied uniformly over a surface, measured as force per unit of area.

reflective: Adjective that refers to the ability of something to reflect light strongly. Such objects can produce a strong bright glare when sunlight bounces off of them. Examples of reflective objects include a mirror, a smooth metal can, a car window, a glass bottle, ice, snow or the watery surface of a lake.

Singapore: An island nation located just off the tip of Malaysia in southeast Asia. Formerly an English colony, it became an independent nation in 1965. Its roughly 55 islands (the largest is Singapore) comprise some 687 square kilometers (265 square miles) of land, and are home to more than 5.3 million people.

species: A group of similar organisms capable of producing offspring that can survive and reproduce.

stomata: (sing. stoma) Tiny openings in the surface of a plant leaf or stem. They allow gases and water vapor to escape. Some plants close their stomata at night. Other plants - those living in very dry areas such as deserts - close them during the day to keep water inside.

sustainable: An adjective to describe the use of resources in a such a way that they will continue to be available long into the future.

temperate: In geography, areas that are cooler than the tropics but warmer than polar regions.

transpiration: (v. transpire) A process in which plants carry moisture from their roots to their leaves, where it is then lost to the atmosphere as vapor.

tropics: The region near Earth's equator. Temperatures here are generally warm to hot, year-round.

vacuum: Space with little or no matter in it. Laboratories or manufacturing plants may use vacuum equipment to pump out air, creating an area known as a vacuum chamber.

vegetation: Leafy, green plants. The term refers to the collective community of plants in some area. Typically these do not include tall trees, but instead plants that are shrub height or shorter.

ventilation: A system that supplies a room with fresh air or processes that move air around and between different rooms.

wave: A disturbance or variation that travels through space and matter in a regular, oscillating fashion.

wavelength: The distance between one peak and the next in a series of waves, or the distance between one trough and the next. It's also one of the "yardsticks" used to measure radiation. Visible light - which, like all electromagnetic radiation, travels in waves - includes wavelengths between about 380 nanometers (violet) and about 740 nanometers (red). Radiation with wavelengths shorter than visible light includes gamma rays, X-rays and ultraviolet light. Longer-wavelength radiation includes infrared light, microwaves and radio waves.

Citations

Journal:​ ​​M.S. Davies Wykes et al. The effect of an indoor-outdoor temperature difference on transient cross-ventilation. Building and Environment. Vol. 168, January 15, 2020, p. 106447. https://doi.org/10.1016/j.buildenv.2019.106447.

Journal: J.S. MacIvor et al. Air temperature cooling by extensive green roofs in Toronto Canada. Ecological Engineering. Vol. 95, October 2016, p. 36. https://doi.org/10.1016/j.ecoleng.2016.06.050.

Meeting:​​ MacIvor, J.S and Margolis, L. 2015. Cooling of a south-facing wall using double-skin green façade in a temperate climate. International Plant Propagators' Society 2014 Annual Meeting. September 20, 2014. Niagara, Ontario, Canada. Acta Horticulturae: Proceedings of the 2014 Annual Meeting of the International Plant Propagators Society, ISHS,2015.64, p. 185, 2015. doi: 10.17660/ActaHortic.2015.1085.30.

Sharon Oosthoek is a freelance science journalist. She likes to write about animals and their habitats. Sharon also really likes chocolate. Her sons have learned to hide their Halloween candy.

# data[].attributes.attachment_link.title
Changing climates can take cooling tips from warm regions

# data[].attributes.attachment_link.description
In the summer of 2019, a blistering heat wave swept across Europe. France was particularly hard hit. In some places, the temperature hit 46° Celsius (115° Fahrenheit). More than 1,400 people died, some in their own homes - buildings that were never designed to withstand the intense heat that has arrived with climate change.

# data[].attributes.attachment_link.readable_text
When it's cold outside, you turn on the heat. When it's hot, you turn on the air conditioning. That's about as much thought as most people ever give to temperature control at home.

You might want to dwell a little longer on the conditioned air that magically wafts out of household vents, however. The way you heat or cool your home has a big effect on the Earth, says John Carmody. He's director of the Center for Sustainable Building Research at the University of Minnesota in Minneapolis.

"Most people don't usually think about where their heat comes from," Carmody says. Yet nearly every type of energy source dumps waste or spews pollution into the air.

South Florida Restoration Science Forum, U.S. Geological Survey

Buildings have a huge impact on the environment. There are more than 81 million buildings in the United States, according to the U.S. Department of Energy. Buildings consume more energy than any other economic category, including transportation and industry. Almost half of the energy that buildings use goes into heating and cooling.

Like Carmody, a growing number of engineers, planners, and architects have been looking for new ways to make buildings less wasteful and kinder to the environment. Improvements have come in many forms, including better insulation, windows, and construction materials.

Architects are also realizing that the size, location, and positioning of a building affects how much energy it uses. Even the arrangement of buildings in a neighborhood makes a difference.

"In the last 10 years," Carmody says, "there has been a major movement toward what you'd call 'green' buildings." Such buildings are sometimes also described as sustainable, environmentally friendly, or healthy.
Temperature control
The amount of energy you use for heating and cooling depends on where you live.

In places such as San Diego, Calif., for instance, the temperature is mild all year round. People rarely have to regulate the temperature of their homes.

Where I live in Minnesota, on the other hand, winters are unbearably cold, and summers can be unbearably hot. Without heaters and air conditioners, we'd be in big trouble. (At least, I know I would be pretty miserable.)

To get a sense of your own environmental impact, you can look at the climate where you live. Ask yourself how often you turn on the heater or the air conditioner, and how high you pump them up.

You might also want to figure out the source of the energy that your house or school uses for temperature control. Most air conditioners run on electricity. Some heaters do, too. If you find a furnace in the basement and radiators around your house, though, that probably means you have a system that burns natural gas or oil to heat water.

These energy sources have their downsides. Electricity, for example, usually comes from power plants that burn coal or use nuclear fuel. Both produce dangerous waste.

And there's energy lost along the way. "Only about a third of the energy generated at a power plant makes its way to a house," Carmody says.

As an alternative energy source, harnessing the power of the wind or sun is becoming more popular in some places. Windmills for generating electricity are springing up from California to Germany. And researchers are working to make solar cells, which absorb light from the sun and convert it into electricity, more efficient.

Sunlight can also be used to heat tanks of water. Still, the technology needs some work. For now, solar power is more expensive than traditional sources. And some places don't have enough reliable sunshine or wind to make these approaches practical.
Windows, walls, and roofs
No matter where the energy comes from to heat or cool your home, simple design and construction choices can have a big effect on how much energy you end up using.

First, consider when your home was built. Old houses tend to be drafty, Carmody says. They lose energy to the outdoors.

Newer buildings have more insulation packed into the walls. Fluffy materials such as fiberglass and Styrofoam have lots of pockets for trapping air. Such a structure holds heat in, just like a cozy sleeping bag. Many environmentalists prefer cellulose fiber, which is made from recycled paper and wood, for insulation.

When it comes to energy efficiency, windows are a big issue. Instead of just looking through them, take a closer look at the windows where you live. If you can feel cold air rushing in even when the window is closed, that's a good sign that you're wasting a lot of energy.

New technologies are drastically improving window performance.

Windows used to be made from single sheets of glass. Today, windows are almost always double-glazed. This means there are two panes of glass set in a frame with an air space between them for insulation. Sometimes, windows are triple-glazed.

Scientists have also developed special coatings for windows. These invisible materials reflect heat. In a double-glazed window, coating the two sides of glass that face each other traps heat between the panes and increases insulation.

Chemists in England recently developed a kind of "smart" window coating. It reflects heat, but only when the window gets warmer than room temperature. If the technology becomes more affordable and practical, it could make windows even better at keeping the inside air in and the outside air out.

On the other side of the temperature fence, researchers from Oak Ridge and Lawrence Berkeley National Laboratories are working on a new type of roofing material that they hope will cut the cost of air conditioning by 20 percent.

If you've ever worn a black T-shirt on a sunny day, you know that dark colors absorb light and create heat. Most roofs are dark, so they absorb infrared and visible light, which makes a building warmer. The idea is to make shingles with colors that reflect certain wavelengths of sunlight. Such "cool" roofs should be available in 3 to 5 years, the scientists say.
Living spaces
Perhaps the most innovative strategy for increasing energy efficiency actually has nothing to do with technology. Instead, architects take advantage of the environment and landscape to control temperature inside a building.

In the northern hemisphere, this can mean installing lots of south-facing windows so that plenty of sunlight can pour in. At the same time, well-designed overhangs keep summer sun out but let winter sun in.

Some people are choosing to live in communities that have been specifically designed to promote energy-efficient living. Village Homes in Davis, Calif., was one of the first of such green, or sustainable, developments.

Completed in 1981, the neighborhood has a network of paths that encourages people to bike or walk instead of drive (and pollute). The development's 240 houses face south for lots of exposure to the sun. Overhangs provide shade. Houses run on solar power. There are lots of trees. And narrow streets have as little pavement as possible.

The strategy seems to be working. The air temperature around Village Homes is 15 degrees F. cooler than surrounding areas that have more pavement. And residents spend between one-third and one-half as much on energy bills compared to more conventional homes in nearby neighborhoods.

"We have a shadier, cooler microclimate," says developer and resident Judith Corbett, who spoke at an environmental design conference in Minneapolis last April. "I don't even have an air conditioner."

As people see communities such as Village Homes thrive, these types of developments are becoming more popular. They're springing up in places such as Colorado, Arizona, Virginia, and Australia.
Zero energy
The U.S. government itself is taking steps to boost the energy efficiency of the nation's buildings. In one project, the Department of Energy has a long-term goal to create a "net-zero-energy" house-a house that wastes no energy.

The Department of Energy's development of "near-zero-energy" homes is one step in that direction. One such house in Tennessee runs completely on electricity for just 82 cents a day. Conventional homes in the same area use between $4 and $5 in electricity a day.

As research on efficient energy use continues, think about what you can do to live a more energy-efficient life in the meantime.

Keep the heat low or off when you're not home. Make sure leaks around doors and windows get patched. Turn off lights, TVs, and computers when they're not needed.

Better yet, if you're cold, put on a sweater and have a hot drink. If you're hot, consider having an ice cream cone or going for a swim.

ENERGY USE IN THE UNITED STATES (in quadrillion BTUs)

Btu, short for British Thermal Unit, is a unit of heat energy. One Btu is the amount of heat needed to raise the temperature of one pound of water 1° F. The heat given off by burning one wooden kitchen match is about 1 Btu.

Source: Energy Information Administration, U.S. Department of Energy

# data[].attributes.attachment_link.description
When it's cold outside, you turn on the heat. When it's hot, you turn on the air conditioning. That's about as much thought as most people ever give to temperature control at home. You might want to dwell a little longer on the conditioned air that magically wafts out of household vents, however.

# data[].attributes.attachment_link.readable_text
What exists in high places, retains water, cools the city and is green all over? How about a green or "living roof"-an energy-saving solution found on many buildings in the GTA and is growing in popularity in the residential sector.

"Green roofs are definitely a growing area of interest with residents- they're excited about the many benefits green roofs offer and their aesthetic value," says Annemarie Baynton, program manager with the City of Toronto's Eco-Roof Incentive Program.

Toronto has played a leading role in North America in developing green roofs as a solution to combat climate change, manage stormwater and help reduce energy consumption.

"Toronto was the first city in North America to introduce a green roof bylaw. It's a mandatory requirement that all new development install a green roof," says Baynton. "This came into effect in 2010 and today, Toronto has more than 600 green roofs."

But what exactly is a green roof and why has the City chosen to mandate its growth and proliferation? Here's what you need to know.
What is a green roof?
According to the City of Toronto, a green roof is a "roof of a building that is partially or completely covered with vegetation...planted over a waterproofing membrane."

"A green roof system is an extension of the existing roof which involves several layers including a waterproof membrane, drainage system, a lightweight growing medium (soil), and plants," says Baynton, noting that common plants found on green roofs include sedums, succulents and other drought and heat-resistant plants that thrive in shallow soil. It's also possible to use native flowering plants to create much-needed pollinator habitat on a green roof. Birds, bees and butterflies can all benefit from greening rooftops.

Baynton points out that green roofs also work well when partnered with solar panels on a roof.

"The two work hand in hand. You can do a green roof underneath and install the panels overtop," she says. "The electronic component of the solar panel can work more efficiently thanks to the air around it being cooled from the green roof."
Why have one?
The benefits to installing a green roof are numerous. According to the National Research Council of Canada, an extensive green roof can lower your energy demand from air conditioning by more than 75 per cent.

The roof also helps absorb sound by as much as 50 decibels.

A more macro look at the effect of green roofs on urban settings includes air cooling. "Cities are warmer because we have more heat-absorbing surfaces and less vegetation when compared to rural areas. Green roofs cool the surrounding air," says Baynton.

This occurs through a process called evapotranspiration. In the same way sweat cools our skin, the process of evapotranspiration allows for the cooling of a plant's leaves through the release and evaporation of water.

"Storm water management is another major benefit. Green roofs capture rainwater reducing storm water runoff into the urban environment, which helps reduce the risk of flooding".

In fact, Green Roofs for Healthy Cities-North America Inc. estimates that in the summer, 70 to 90 per cent of the precipitation that falls on green roofs is maintained while in winter, 25 to 40 per cent of the precipitation that lands is retained.
Worldwide growth
According to the 2016 Green Roofs for Healthy Cities industry survey, Toronto took a top spot for the greatest square footage of green roof installations in North American cities. Other cities installing an increasing number of roofs included followed by Chicago, Washington, D.C. and Seattle.

Over in Europe, The European Federation of Green Roof Associations reports that there was 86 million square metres of green roofs in Germany in 2014 with another eight million added annually. (Germany has the largest number of green roofs within Europe.)

Like Toronto, Germany has changed building policies at the municipal level as well as offered incentives to encourage this kind of growth.

What you should know
If you're interested in a green roof, there are a few things you should keep in mind starting with the fact that these roofs are most commonly installed on flat roofs.

Maintaining a green roof involves some maintenance like any natural landscape.

"You need to water the plants if it's been too long without rain. And sometimes you need to weed," says Baynton.

At minimum, she suggests checking in on the living roof in the spring and fall for routine maintenance, which includes inspecting the drains to see that they're clear as well.

"But it's generally recommended to go up at least once a month. This is especially important during the first five years when it's establishing itself and may be more vulnerable," adds Baynton.

It's also best to get such a roof professionally installed rather than build it yourself. To do so, consider the City of Toronto's Eco-Roof Incentive Program which offers grants to support the building of green roofs. To date, the program has supported over 420 projects, creating over 800,000 square metres of eco-roof space in Toronto (equivalent to about 101 Canadian football fields).

# data[].attributes.attachment_link.title
Are green roofs just a trend? How this sustainable solution can help you save energy - Toronto | Globalnews.ca

# data[].attributes.attachment_link.description
What exists in high places, retains water, cools the city and is green all over? How about a green or "living roof"-an energy-saving solution found on many buildings in the GTA and is growing in popularity in the residential sector.

# data[].attributes.attachment_link.readable_text
Green roofs have been proven to help reduce heat islands. This page provides a brief overview of the role of green roofs in mitigating the heat island effect, including green roof types, other environmental and social benefits, and cost-benefit considerations.

A green roof, or rooftop garden, is a vegetative layer grown on a rooftop. Green roofs provide shade, remove heat from the air, and reduce temperatures of the roof surface and surrounding air. Using green roofs in cities or other built environments with limited vegetation can moderate the heat island effect, particularly during the day. Green roof temperatures can be 30-40°F lower than those of conventional roofs and can reduce city-wide ambient temperatures by up to 5°F. In addition, green roofs can reduce building energy use by 0.7% compared to conventional roofs, reducing peak electricity demand and leading to an annual savings of $0.23 per square foot of the roof's surface. These temperature reduction and energy efficiency benefits are a key contributor to the growing popularity of green roofs in the United States. In 2016, the North American green roof industry is estimated to have grown by more than 10% over 2015, continuing industry's growth trend over the past decade. That year, a sample of industry stakeholders reported nearly 900 green roof projects totaling more than four million square feet in 40 U.S. states and six Canadian provinces.

Types of Green Roofs

Green roofs can be installed on a wide range of buildings, from industrial facilities to private residences. There are two types of green roofs: extensive and intensive.

Extensive Green Roofs

Intensive Green Roofs

Tend to be simpler, with hardy plants and a growing medium depth of two to four inches

Require the least amount of added structural support since they are lightweight

Need little maintenance once established

Tend to be more complex, such as a fully accessible park complete with trees

Resemble conventional gardens or parks

Require more structural support since they are heavier

Require a higher initial investment

Require more intensive maintenance

Both types of green roofs consist of the same basic layering components with a number of barriers to prevent water or root damage to the structure, a drainage layer to aid in water drainage, as well as a growing medium and vegetative layer. The Common Green Roof Layers figure (below) represents the most common design of a green roof, although not all the layers shown are found on every green roof.

Green Roofs vs. Cool Roofs

Cool roofs present another option to reduce the heat island effect. Cool roofs are made of highly reflective and emissive materials that remain cooler than traditional materials during peak temperatures. While green roofs often have initially higher costs than cool roofs, green roofs typically have a longer expected life. Both cool and green roofs provide benefits of lower surface and air temperatures, and decreased energy demand. However, green roofs offer added benefits such as reducing and filtering stormwater runoff; absorbing pollutants and carbon dioxide; providing natural habitat; and in the case of intensive green roofs, serving as recreational green space. Cool roofs are best suited for projects with limited budgets and a primary focus on energy savings, while green roofs are preferred when lifecycle costs, public benefits, and broader environmental impacts are of interest. Both options are important strategies for mitigating heat island effects.

Green Roofs Photo Gallery

Co-Benefits of Green Roofs

Green roofs and other heat island mitigation strategies offer a number of co-benefits (see figure below). Benefits specific to green roofs include:

Reduced air pollution and greenhouse gas emissions: By lowering air-conditioning demand, green roofs can decrease the associated air pollution and greenhouse gas (GHG) emissions from conventional power sources. Vegetation can also remove pollutants and GHGs from the air through dry deposition and carbon sequestration and storage, respectively.

Reduced energy use: Green roofs remove heat from the air through the process of evapotranspiration, and also act as insulators for buildings, reducing the energy needed to provide cooling and heating.

Improved human health and comfort: Green roofs, by reducing heat transfer through the building roof, can improve indoor comfort, and lower the incidence of heat stress associated with heat waves.

Improved quality of life: Green roofs provide aesthetic value and habitat for plant and animal species. They improve human interaction with nature by introducing green space into the built environment. Such connections to nature have been shown to benefit human physical and mental health and productivity, and reduce blood pressure and hospital stays.

Enhanced stormwater management and water quality: Green roofs can reduce and slow stormwater runoff in the urban environment, and also filter pollutants from rainfall. Green roofs can retain nearly all storm-related precipitation during the summer months, with lower retention during the winter months (< 20%). The actual stormwater management potential of green roofs is dependent on the season and rainfall patterns.

Estimating the Environmental Effects of Green Roofs

The EPA-published case study, Estimating the Environmental Effects of Green Roofs, demonstrates the environmental and health benefits of green roofs for Kansas City, Missouri. The case study lays out a replicable analytical framework using free quantitative tools created by EPA and others that state and local decision-makers and practitioners can use to assess the multiple benefits of green roofs. The study found that the over 700,000 ft ² total coverage of green roofs in Kansas City installed between 1999-2020 would result in avoided emissions of 384 pounds of nitrogen oxide, 734 pounds of sulfur dioxide, and 269 tons of carbon dioxide in 2020. These emissions reductions equate to monetized health benefits of $35,500-$80,500.

Costs of Installing and Maintaining Green Roofs

The estimated costs of installing and maintaining a green roof vary by the type of green roof. For example, a simple extensive roof without public access could be as little as one-tenth to one-third of the cost to construct an intensive green roof intended for public access. While the initial costs of green roofs can be higher than those of conventional materials, building owners can help offset some of the differences in these costs through reduced energy costs and stormwater management fees, and potentially by the longer lifespan of green roofs compared with conventional roofing materials. Typical maintenance includes fertilization, irrigation, weed control, and replanting when necessary. Intensive green roofs might require maintenance exceeding that required for extensive roofs to maintain their aesthetic and public access uses.

Researchers at Lawrence Berkeley National Laboratory conducted a lifecycle cost analysis of green roofs, cool roofs, and conventional roofs. They found that while green roofs are more expensive than cool or conventional roofs, they provide significantly higher relative benefits per square foot over a 50-year lifecycle (e.g., energy cost savings, avoided emissions, reduced stormwater fees). Compared to conventional roofs, the benefits of extensive green roofs are $14 more per square foot, while cool roofs provide benefits of $2 more per square foot relative to conventional roofs.

More Information

More details on this topic are available in Chapter 3 of EPA's Reducing Urban Heat Islands: Compendium of Strategies, which covers the following topics:

How green roofs help to reduce heat islands

Green roof types

The benefits and costs of green roofs

Other factors to consider in using green roofs

Green roof initiatives

Tools and resources to further explore this technology

General Services Administration. 2011. " The Benefits and Challenges of Green Roofs on Public and Commercial Buildings."

Santamouris, M. 2014. "Cooling the cities - A review of reflective and green roof mitigation technologies to fight heat island and improve comfort in urban environments," Solar Energy 103:682-703.

Sailor, D.J., T.B. Elley, and M. Gibson. 2011. " Exploring the building energy impacts of green roof design decisions - A modeling study of buildings in four distinct climates," Journal of Building Physics 35(4):372-391.

Green Roofs for Healthy Cities. 2017. "2016 Annual Green Roof Industry Survey: Executive Summary."

City of Los Angeles, Environmental Affairs Department. 2006. " Green Roofs-Cooling Los Angeles (A Resource Guide)." Los Angeles, CA.

Beatley, T. and P. Newman. 2013. " Biophilic cities are sustainable, resilient cities." Sustainability 5(8):3328-3345.

U.S. Environmental Protection Agency (EPA). 2009. " Green Roofs for Stormwater Runoff Control."

Sproul, J., M.P. Wan, B.H. Mandel, and A.H. Rosenfeld. 2014. " Economic comparison of white, green, and black flat roofs in the United States." Energy and Buildings 71:20-27.

# data[].attributes.attachment_link.title
Using Green Roofs to Reduce Heat Islands | US EPA

# data[].attributes.attachment_link.description
Green roofs have been proven to help reduce heat islands. This page provides a brief overview of the role of green roofs in mitigating the heat island effect, including green roof types, other environmental and social benefits, and cost-benefit considerations. A green roof, or rooftop garden, is a vegetative layer grown on a rooftop.

# data[].attributes.attachment_link.readable_text
A color developed by Egyptians thousands of years ago has a modern-day application as well - the pigment can boost energy efficiency by cooling rooftops and walls, and could also enable solar generation of electricity via windows.
Egyptian blue, derived from calcium copper silicate, was routinely used on ancient depictions of gods and royalty. Previous studies have shown that when Egyptian blue absorbs visible light, it then emits light in the near-infrared range. Now a team led by researchers at the Department of Energy's Lawrence Berkeley National Laboratory (Berkeley Lab) has confirmed the pigment's fluorescence can be 10 times stronger than previously thought.

Measuring the temperature of surfaces coated in Egyptian blue and related compounds while they are exposed to sunlight, Berkeley Lab researchers found the fluorescent blues can emit nearly 100 percent as many photons as they absorb. The energy efficiency of the emission process is up to 70 percent (the infrared photons carry less energy than visible photons).

Berkeley Lab scientists measured the temperature rise above air temperature observed in full sun for five pigment-coated samples, each 75 millimeters square. The white and black samples show low and high temperatures.
Credit: Berkeley Lab

The finding adds to insights about which colors are most effective for cooling rooftops and facades in sunny climates. Though white is the most conventional and effective choice for keeping a building cool by reflecting sunlight and reducing energy use for air conditioning, building owners often require non-white colors for aesthetic reasons. For example, bright-white asphalt shingles are almost never used on sloping residential roofs.

Berkeley Lab researchers have already shown that fluorescent ruby red pigments can be an effective alternative to white; this insight on Egyptian blue adds to the menu of cooling color choices. Further, they found that fluorescent green and black colors can be produced with yellow and orange co-pigments. The new findings were recently published in the Journal of Applied Physics.

In addition to its cooling potential for buildings, Egyptian blue's fluorescence could also be useful in producing solar energy. Used on windows tinted with the blue, photovoltaic cells on the edges can convert the fluoresced near-infrared energy to electricity.

Substantial research over the years from Berkeley Lab's Heat Island Group has found that reflective roofs and walls can cool buildings and cars. This reduces the need for air conditioning and mitigates the urban heat island effect. By reflecting the sun's rays back to space, these cool materials also release less heat into the atmosphere, thus cooling the planet and offsetting the warming effects of substantial amounts of greenhouse gas emissions.

This work was led by Paul Berdahl of the Heat Island Group as part of the Cool Walls project supported by the Electric Program Investment Charge program of the California Energy Commission.

# data[].attributes.attachment_link.title
Ancient pigment can boost energy efficiency

# data[].attributes.attachment_link.description
A color developed by Egyptians thousands of years ago has a modern-day application as well - the pigment can boost energy efficiency by cooling rooftops and walls, and could also enable solar generation of electricity via windows. Egyptian blue, derived from calcium copper silicate, was routinely used on ancient depictions of gods and royalty.

# data[].attributes.attachment_link.readable_text
Case Western Reserve civil engineer applies 'thermochromic' treatment to roofing materials, which change color to reflect or absorb heat

In Bill Yu's future world, the roof of your house might change its colors from dark blue to light blue when the sun comes out-and both your pocketbook and the planet might thank you for it.

Yu, a civil engineering professor at Case Western Reserve University, calls them "chameleon roofs," describing existing asphalt shingles coated with plastic film or a spray paint that changes color depending on the amount of natural light.

Xiong (Bill) Yu

A darker roof will absorb more heat from the sun and help to heat a house in winter; a lighter-colored roof will reflect the light and help keep a home cooler in the summer, Yu said.

About 40 percent of an average building's energy use and expense comes from heating and cooling, Yu said, making the changeable roof system potentially a money-saving innovation for homeowners and businesses alike. Buildings also use about 30 percent of the world's electricity, much of it still generated from fossil fuels.

Yu-and collaborator Jianying Hu, a former postdoctoral researcher at Case Western Reserve now at Southeastern University-experimented with various colors and materials in different climate situations. In addition, they are testing another system to more efficiently scatter or concentrate collected light particles to increase the efficiency of the material.

Their work published in a new research paper detailing this "adaptive thermochromic roof system" in the journal Energy & Buildings.

The system has not yet been tried on residential or commercial roofs, but computer models across climates in seven U.S. geographic regions projected success rates of varying degrees.

Samples of black, blue and red paint which change color from exposure to light.

On average, the coatings could lead to a 5.4 percent reduction in energy demand in winter and 13.3 percent reduction in summer, their modeling showed. The simulations and energy analysis were run on U.S. Department of Energy software.

The thermochromic roof system was most effective in San Francisco, showing a combined savings of more than 47 percent in heating and cooling over the course of a theoretical year.

Yu came up with the idea as a way to improve upon the U.S. Department of Energy's "Cool Roof" program, which advocates for roofs painted white to reflect light and heat in warmer areas of the country, which helps reduce the phenomenon in bigger cities known as the "urban heat island effect". "In a world of climate change, you have areas experiencing wilder swings in temperature," Yu said, "so having a roof that reacts to both heat and cold could be beneficial no matter the time of year."
For more information, contact Mike Scott at mike.scott@case.edu.

# data[].attributes.attachment_link.title
"Chameleon roofs" of future could save money, energy

# data[].attributes.attachment_link.description
Case Western Reserve civil engineer applies 'thermochromic' treatment to roofing materials, which change color to reflect or absorb heat In Bill Yu's future world, the roof of your house might change its colors from dark blue to light blue when the sun comes out-and both your pocketbook and the planet might thank you for it.

# data[].attributes.attachment_link.readable_text
There are many types of roof systems available, but the surface solar reflectance of the roofing product-the outermost layer of the roof exposed to the sun is, also known as the roof covering-determines whether the roof is cool or not. There are cool options for nearly all types of roof coverings.

Paths to a Cool Roof

Cool roofing products usually cost no more than comparable conventional roofing products. The easiest and least expensive way to make your roof cool is to choose a cool covering during new construction, or when your existing roofing covering needs to be replaced. Certain types of roofing products can also be retrofitted with cool coatings, but this will incur extra material and labor costs.

Color Choice

White roofing products stay coolest in the sun, reflecting about 60 - 90% of sunlight. However, since about half of sunlight arrives as invisible "near infrared" radiation, we can boost the solar reflectance of dark materials by using special pigments (colorants) that preferentially reflect this invisible light. Such "cool colored" products typically reflect about 30 - 60% of sunlight, staying cooler than conventionally colored products (though not as cool as white).

Products for Steep Roofs (Pitch > 2:12)

Products for Low -Sloped Roofs (Pitch ≤ 2:12)

Built-up roofs consist of a base sheet, fabric reinforcement layers, and a surface layer.
How they can be made cool: The surface layer can be made different ways,-typically a cap sheet or ballast-to protect the lower layers from wind and weather. (A cap sheet is typically a fiberglass web coated in asphalt, or a modified bitumen sheet membrane, and is often surfaced with mineral granules.)
Cool options:

Choose a cap sheet with a factory-applied reflective mineral surface or reflective coating

Substitute reflective marble chips or gray slag for dark gravel in a flood coat of asphalt

Field-apply a reflective coating

Modified bitumen sheet membranes have one or more layers of plastic or rubber material with reinforcing fabrics, and are surfaced with mineral granules or a smooth finish. These can also be used to surface a built-up roof, producing a "hybrid" roof.
Cool options: Choose a cap sheet with a factory-applied reflective mineral surface or reflective coating.

Products for Steep and Low-sloped Roofs

Green (Vegetative) Roofs

You may also consider installing a green roof., which refers to the presence of vegetation rather than the color. Green roofs are ideal for urban buildings with low-sloped or shallow-pit roofs, and can include anything from basic plant cover (extensive vegetative roof) to a garden. or even small trees (intensive vegetative roof). The primary reasons for using this type of roof include managing storm water and creating an attractive and enjoyable rooftop open space.

Green roofs are "inverted" roofs, meaning that the waterproofing membrane is located beneath the plants and most of the roof components. In that location the membrane is well protected from the sun's degrading UV radiation, but leaks are also much more challenging to find and difficult to repair. Green roofs are considerably heavier and more expensive to construct and maintain than non-vegetated roofs. The underlying structure needs to be able to bear the additional load and the plant cover typically requires some maintenance. You should carefully assess your property, building structure, local climate, and consult professionals before deciding to install a green roof.

Green roofs are cooled primarily by the evaporation of water from plant surfaces rather than by reflection of sunlight. The soil layer also provides additional insulation as well as thermal mass.

Deciding Whether and When to Install a Cool Roof

When deciding whether to install a cool roof, you'll need to determine whether the energy savings and other benefits will justify the cost premium (if any). How much energy you will save depends on several factors such as your home's climate and surroundings, the extent to which the roof assembly is insulated, the type of roof you have, and the efficiency of your heating and cooling system.
If you are building a new home, you can decide during the planning phase what type of roof to install and whether it should be a cool roof. If you want to convert an existing roof into a cool roof, you have three basic options:

Install a cool roofing product when your existing roof

Install a cool roofing product before your existing roof reaches the end of its service life (could be wasteful)

Apply a cool roof coating to the existing roof, if the type of roof is suitable for coating

Cost and Energy Savings

A cool roof does not necessarily cost more than a non-cool roof, especially if you are installing a new roof or replacing an existing one. However, converting a standard roof that's in good condition into a cool roof can be expensive.

Climate and Environment

Your climate is an important consideration when deciding whether to install a cool roof. Cool roofs achieve the greatest cooling savings in hot climates, but can increase energy costs in colder climates if the annual heating penalty exceeds the annual cooling savings.

Moisture Control

In warm, moist locations, where roofs are subject to algae or mold growth, dark growths may be more visible on light-colored roofs than on dark roofs. Some roof coatings include special chemicals that prevent mold or algae growth for a few years.

In cold climates, roofs can accumulate moisture through condensation, and it is possible that cool roofs might be more susceptible to accumulating moisture than dark roofs of the same design. Condensation can be avoided using proper design techniques.

Finding Cool Roofing Products

Cool roof qualifications, such as minimum values of solar reflectance and thermal emittance, vary by standard or program, location, building type, and roof slope. Therefore, there is no single definition of a cool roof. However, the Rated Products Directory of the Cool Roof Rating Council reports the solar reflectance and thermal emittance of thousands of roofing products.

# data[].attributes.attachment_link.description
There are many types of roof systems available, but the surface solar reflectance of the roofing product-the outermost layer of the roof exposed to the sun is, also known as the roof covering-determines whether the roof is cool or not. There are cool options for nearly all types of roof coverings.

# data[].attributes.attachment_link.title
New Smart-Roof Coating Enables Year-Round Energy Savings - Berkeley Lab

# data[].attributes.attachment_link.description
Berkeley Lab scientists have invented an energy-free, smart-roof coating that regulates household temperature year-round.

# data[].attributes.attachment_link.readable_text
Roofs, and the rainbow of colors used in roofing materials, are getting cooler and cooler, thanks to research by Berkeley Lab's Environmental Energy Technologies Division (EETD). The cooler roofs get, the more energy and money they save. A new program in cool materials will soon result in the first cool shingle for residential roofs becoming available on the market.

Since the mid-1980s, Berkeley Lab researchers have studied the effects of increasing the solar reflectance of roofs. "Cool" roofs, which reflect more of the sun's radiation than conventional roofs, keep houses and other structures cooler, lower their air-conditioning energy use, and reduce the "urban heat island effect," in which air temperatures in urban areas are higher than surrounding rural areas.

Since dark surfaces are better heat absorbers, traditional cool roofs are white. Berkeley Lab research has demonstrated that raising the solar reflectance of a roof from about 20 percent (dark gray) to about 55 percent (weathered white) can reduce cooling energy use by 20 percent.

Flat-roofed commercial buildings are often fitted with white roofs, but U.S. homeowners typically demand nonwhite roofs. Cool-colored, nonwhite roofs meet that need. It is possible to create a nonwhite cool roof by using colorants or pigments that reflect the invisible, near-infrared radiation that accounts for over half of the energy in sunlight.

"Our research estimates that the potential net energy savings in the U.S. achievable by applying white roofs to commercial buildings and cool-colored roofs to houses is more than $750 million per year," says Hashem Akbari, an EETD researcher and head of the Heat Island Group.

The Heat Island Group's research has shown that, regionally, widespread application of cool roofs can reduce ambient air temperatures and retard smog formation. Cool roofs can also reduce peak electrical demand in the summer, which helps reduce strain on the aging electricity grid when relief is most needed. Lower temperatures on the roofs may also increase the life of a roof, according to preliminary research by the group.

Thanks to the work of Akbari's team, the roofing industry in recent years has adopted voluntary industry standards for measuring the reflectance of roofing materials and has set up the Cool Roof Rating Council to develop labels that inform buyers about the relative coolness of various products used in roofing - that is, their ability to reflect solar energy and release heat through thermal radiation.

The building-materials industry has brought a number of products to the marketplace that help increase the reflectance of roofs, including elastomeric coatings, single-ply membranes, tiles, and metal roofing. And the Environmental Protection Agency's Energy Star program certifies cool roof products with its voluntary labeling; EPA maintains a web-based guide to Energy Star roofing products.

However, technical barriers to getting cool roofs on homes still remain. Existing white and nonwhite cool coatings are fine for the low-slope roofs of commercial and industrial buildings and apartment structures, where white is acceptable. But on the high-slope roofs of single-family homes, which can been seen from the street, the market is dominated by colorful shingles, tiles, metal products, and wood shakes. Most homeowners don't want white roofs. Asphalt shingles account for 47 percent of the roofing market for residences in the western states, according to industry sources.

To bring cool roofs to the high-slope residential market, research was needed to identify cool color pigments and a different way of manufacturing asphalt shingles. Thanks to a research project funded by the California Energy Commission and the U.S. Department of Energy, consumers will soon see a variety of new cool-colored roofing products to help them save energy and increase the comfort of their homes.

Berkeley Lab is working with Oak Ridge National Laboratory, two pigment manufacturers, and ten roofing manufacturers who collectively produce about 90 percent of the residential roofing products in the United States. The industrial partners are 3M, American Roof Tile Coating, BASF, Custom-Bilt Metals, Elk Manufacturing, Ferro, GAF, Hanson Roof Tile, ISP Minerals, MCA, Monier Lifetile, and Shepherd Color Company.

"Most commercially available roof shingles are optically dark," says Akbari. "Their solar reflectances range from 5 to 25 percent, depending on color. Even the majority of nominally 'white' roof shingles are grayish, and have a solar reflectance of about 25 percent, which is much lower than the 70 percent solar reflectance of white tiles or white metal panels. Since many homeowners prefer nonwhite roofs, we are working to develop cool-colored roof products."

Cooler pigments

Building a cooler color shingle starts with finding cooler pigments. EETD's Hashem Akbari, Paul Berdahl, and Ronnen Levinson have been testing commercially available pigments to measure their solar spectral reflectance - their reflectance versus wavelength over the solar spectrum. For a given color, the ideal pigment is one that reflects as much as possible of the invisible radiation in the near-infrared range.

The research team has developed a pigment database with a variety of colors, including browns, blues, purples, greens, and reds, that are highly reflective to near-infrared radiation. When tiles colored with standard pigments were compared with tiles colored with cool pigments, the solar reflectance of the cool pigments was from 15 to almost 40 percent better than color-matched conventional pigments. And with metal roofing panels, while to the eye a cool brown and a standard brown may appear almost the same color, the cool brown is almost 20 percent more solar-reflective than the conventional brown (27 percent versus 8 percent).

In addition to testing materials in the lab, Levinson, Berdahl and Akbari have adapted a mathematical model to describe how pigments scatter and transmit light. They will apply the model to develop more reflective cool-colored roofing materials.

Using the pigment database and the model, the team is now developing design software for the roofing industry dealing with cool-color coatings. The software estimates the reflectance of the coating using the absorption and scattering properties of the pigment as well as coating composition and geometry. It provides recipes for manufacturing pigmented coatings that maximize the solar reflectance for a given color.

Cooler tiles, panels, and shingles

The next step is to figure out how to apply pigments to relatively simple roofing products such as tiles, metal panels, and wood shake. The team has identified a number of cool pigments appropriate for use in coating metal panels and concrete and clay tiles. Tile roofs are a growing preference in more expensive houses of the western and southern states.

One manufacturer of metal roofing has already switched most of its product line to these cooler pigments, since the cost was about the same, and it added value for their customers. The team's current efforts focus on asphalt shingles, a more challenging technical problem.

Shingles are produced in a multi-step process. Roofing granules (small crushed rocks) are manufactured, and color is applied to them; the granules are then used to coat asphalt-saturated fiberglass sheets.

Cool shingles require cool granules. The Berkeley Lab team and its industrial partners have developed a two-layer system for manufacturing cooler roofing granules. In their process, granules are precoated with an inexpensive pigment that is very reflective at near-infrared wavelengths. In the second step, the cool color pigment is applied. The first pigment helps increase the reflectance of granules - it reflects even more light than the cool color pigment would by itself, reducing the amount of near-infrared light absorbed by the granule's dark surface.

The industrial partners have now manufactured more than 50 prototype cool shingles, 30 tiles and tile coatings, and 20 metal panel prototypes, including a cool black shingle - 18 percent reflective, well above the 4-percent reflectance of conventional black shingles.

Field testing and market acceptance

To test the field performance and durability of these coatings, Berkeley Lab has teamed with Oak Ridge National Laboratory. The Oak Ridge team has set up a steep-slope assembly test apparatus on its grounds in Oak Ridge, Tennessee, where they are evaluating a variety of samples from the manufacturing partners. Andre Desjarlais, William Miller and their associates have installed representative cool roofing materials at the Oak Ridge roof testing facility. They are measuring the changes in physical and chemical composition of the samples as a result of ultraviolet light, weathering, and temperature changes.

The joint Berkeley Lab-Oak Ridge team has also set up weathering panels throughout California to monitor the performance of roofs using test materials from the manufacturing partners. There are seven test sites located throughout the state, in six different climate zones, ranging from mild to severe. Sites are located from the far north of the state, in McArthur, to Meloland at the California-Mexico border. The project team is also collaborating with the Sacramento Municipal Utilities District to measure energy savings and changes in temperature and humidity inside test houses in Sacramento.

A number of the new cool coatings are already available on the market through the manufacturing partners. "Since the start of this research," says Akbari, "the solar reflectance of commercially available clay and metal products has increased from the 5 to 25 percent range to the 30 to 45 percent range. Working with our industrial partners, we hope to produce shingles with a solar reflectance of 25 percent or higher, qualifying for an Energy Star cool-roof label." He adds that "some of the products resulting from this research will also qualify as cool roofs in the California building energy code," the 2005 Title 24 California Building Energy Efficiency Standard.

Additional information

# data[].attributes.attachment_link.description
Contact: Allan Chen, a_chen@lbl.gov Roofs, and the rainbow of colors used in roofing materials, are getting cooler and cooler, thanks to research by Berkeley Lab’s Environmental Energy Technologies Division (EETD). The cooler roofs get, the more energy and money they save. A new program in cool mate…