Other roof shingles can be coated at the factory or in the field to make them more reflective. Tile roofs can be made of clay, slate, or concrete. Tiles can be glazed to provide waterproofing or coated to provide customized colors and surface properties.
How they can be made cool: Some are naturally reflective enough to achieve cool roof standards, and surface treatments can transform tiles with low solar reflectance into cool roof tiles. Metal roofs are available with natural metallic finishes, oven-baked paint finishes, or granular coated surfaces. How they can be made cool: Unpainted metals are typically good solar reflectors but poor thermal emitters, so they rarely satisfy low slope cool roof requirements.
Painting a metal roof can increase its solar reflectance and thermal emittance, allowing it to achieve cool roof status. Alternatively, you can apply cool reflective coatings. You may also consider installing a green roof. Green roofs are ideal for urban buildings with flat or shallow-pit roofs, and can include anything from basic plant cover to a garden.
The primary reasons for using this type of roof include managing storm water and enjoying a rooftop open space. Green roofs also provide insulation, lower the need for heating and cooling, and can reduce the urban heat island effect.
This roof type can be much more expensive to implement than other efficient roof options, so you should carefully assess your property and consult a professional before deciding to install a green roof. How much energy you will save depends on several factors such as your home's climate and environment, how well insulated your current roof is, 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:. If your roof is in poor condition or near the end of its life, it is usually best to re-cover, replace, or retrofit the roof. Such urban nightmares are likely to happen ever more frequently in the future, both because of the expansion of urban areas and because of climate change.
Predicted urban expansion in the U. Several studies suggest that climate change could itself crank up the urban heat island effect. A combination of rising temperatures and high humidity is already predicted to make parts of the Persian Gulf region the first in the world to become uninhabitable due to climate change.
Another option is not to whitewash roofs, but to green them with foliage. This is already being adopted in many cities. In , San Francisco became the first American city to make green roofs compulsory on some new buildings.
Evidence here is fragmentary. But Georgescu found a bigger direct cooling effect from white roofs. Vincenzo Costanzo, now of the University of Reading in England, has reached a similar conclusion for Italian cities. But green roofs may have other benefits. A study in Adelaide , Australia, found that besides delivering cooling in summer, they also act as an insulating layer to keep buildings warmer in winter.
There is a third option competing for roof space to take the heat out of cities — covering them in photovoltaic cells. PV cells are dark, and so do not reflect much solar radiation into space. But that is because their business is to capture that energy and convert it into low-carbon electricity. The research, published in the journal Scientific Reports last year, found that in a city like Sydney, Australia, a city-wide array of solar panels could reduce summer maximum temperatures by up to 1 degree C.
That is the theory, but there are concerns about whether it will always work in practice. Studies into the impact on local temperatures of large solar farms in deserts have produced some contradictory findings. For while they prevent solar rays from reaching the desert surface, they also act as an insulating blanket at night, preventing the desert sands from losing heat. The lesson then is that light, reflective surfaces can have a dramatic impact in cooling the surrounding air — in cities, but in the countryside too.
Whitewashed walls, arrays of photovoltaic cells, and stubble-filled fields can all provide local relief during the sweltering decades ahead. But policymakers beware. Conversely, the EPDM building typically has a 7. On a building as large as these two, nearly 8 degrees means a lot in terms of the additional energy required to maintain a consistent temperature for the building's tenants.
Over the course of a typical hot August day in Scottsdale Arizona, a white roof is 4. During the hottest point in the day inside the building pm , a white roof is 8. During the maximum internal temperature increase hours of am — pm, a white roof is 6. Based on this data, we would suspect that the August kilowatt consumption of the building with the PolyKool roof should have reduced by approximately 7.
According to maintenance supervisor Chris Peterson, all other items remained virtually unchanged from , and that the installation of the PolyKool roof system was the only substantial difference in In August , the kilowatt consumption was , — a 7.
Again, this is on a building with a concrete roof deck. If the building had a plywood roof deck which is much more typical in Arizona and if the SRI value of the materials used were higher is typical of most high-quality roof coatings , the energy savings would be even greater. Starkweather Roofing has begun performing similar analysis using buildings with plywood roof decks as well as higher SRI value roof coatings to compare the results.
The PolyKool cool roof is on average 12 degrees But that includes overnight when there is no direct sunlight. Figure 2. The EPDM roof was on average That's a difference of The study also identified several large-scale white-roof installations, including at Auckland International Airport, shopping centres and commercial buildings, but the effect was less clear.
This research suggests that there is potential for white-roof installations to significantly reduce the amount of energy needed to cool buildings. This would in turn reduce greenhouse gas emissions and also help us to adapt to rising temperatures. But research carried out so far suggests white roofs could be a viable approach to minimising the heat taken up by buildings during hotter parts of the year. White roofs can also help reduce the temperature of whole cities.
Many city centres include large buildings made of concrete or other materials that collect and store solar heat during the day. When cities are hotter, they use more energy for cooling.
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