When you consider how a building keeps cool, the most common thing that comes to mind is air conditioning. But the first real line of defense against the heat is a building's roof. And a hot day in the life of a good roof should include releasing -- not storing and absorbing -- the sun's rays.
Think of it this way: If you're sitting on a chair covered in black fabric and you go to the kitchen for a cup of coffee, your chair will likely be warm when you get up -- and it will stay warm until you return. But if your chair is metal, clay, molded plastic or slate, for example, it might be slightly warm to the touch when you get up, but it will be entirely cooled by the time you return. Traditional shingle roofing materials hold and transfer heat in a similar way. Roofing tiles made of felt-like materials overlaid with asphalt and tar will hold heat, and even transfer it downward into a structure, while other types of roofing will reflect light and heat upward and away from a building instead.
Roofing materials and colors impact how buildings -- and even entire cities -- handle heating and cooling. United States Energy Secretary Stephen Chu even suggested that painting all roofs and roads white or light-colored could reduce the electricity costs of running air conditioning by 10 to 15 percent [source: Connor]. Is it that simple?
Before grabbing a ladder and a can of patio furniture paint and exterior primer, see what roofing materials and techniques -- from the traditional to the high-tech -- have proven to work well in warmer climates.
1.Overlays and Radiant Barriers
Using an umbrella or a wide-brimmed straw hat on a hot day at the beach helps keep the sun at bay. Technology is bringing cover-ups to roofing as well. These cool-roof coatings have advanced in recent years, and more developments are underway. Elastomeric sealants, foam sprays, ceramic-based paints and even "recycled waste cooking oil" treatments are making gains in providing ways to cool existing roofs by applying coats of overlay that reflect heat away . Built Up Roofing (BUR) is one method for applying cool-roof surface coatings over traditional asphalt or tar roofing. Different claims regarding ease of application, durability and energy savings vary by manufacturer, but researching cool-roof overlays or coatings and consulting with a local roofing contractor and local building codes can help in sorting through what's working well in different regions.
A technology on the flipside of an overlay is a roof underpinning, or sub-roof system called a radiant barrier. This under-the-roof application involves installing a reflective material, such as aluminum, or even a specialized reflective spray treatment that's installed into an attic or space between a home's interior and the roof. These act as barriers to keep heat up and out of a home. Costs vary from about 15 to 75 cents per square foot, but those with added insulating features can cost more. But with a possible savings of about Rs14000 annually (depending on the region), the installation fees may be worth the price.
2.Slate Tile
Roofing with slate tiles is a centuries-old European tradition that made its way to the Americas in the early 17th century. Slate is durable and beautiful, with a natural color range, and it lasts a long time with little maintenance. Light colored and earth-toned slate help in reducing the heat absorbed by a building because it has natural reflective properties. It also wears to a nice finish over time.
Some downsides to using slate are its upscale price and heavy weight. While slate is among the most beautiful roofing treatments, especially in re-creating Mediterranean and Spanish architecture styles, it is costly and harder to transport than lighter, less breakable materials. Its extensive use worldwide is due to its popularity as a cool roofing material for hot climates and its widespread availability. In areas without natural slate reserves, it is an expensive option. Reclaimed or salvage slate is available in some areas, but installation and transport costs still add up.
3.Terra Cotta and Clay
Most regions of Kerala, Tamilnadu, Andhra Pradesh and the Indian northwest have tons of heat and sunshine, and an abundance of Mission- or terra cotta roofs. Some ancient sites have clay and terra cotta tiles that have survived the test of time and relentless centuries baking in the sun. Basic clay roofing is light in color and doesn't retain as much heat as a darker roof. Modern clay tiles have paint treatments to make them look like more expensive slate or traditional terra cotta and to add weatherproofing and reflective capabilities.
Traditional rust or sienna-colored terra cotta tiles keep buildings cool through their shape as much as their composition. Terra cotta tiles go through a baking process in ovens, or kilns, which makes them harder and less porous in terms of holding lots of heat. Most often they're molded into a half-barrel or "S" shape, forming interlocking arches across a roof. Space beneath the arch of each tile allows for air and water circulation and runoff, which prevents heat capture and keeps the home below cooler.
Many clay and terra cotta roofs sit on top of concrete and stucco homes, and with good reason. These materials are heavy and need solid foundations for load bearing and wind and earthquake resistance. Another consideration with terra cotta roofing is that cold and wet weather often make tiles snap. Newer processes and treatments prevent this from happening, but checking for durability and temperature resistance is a good idea.
4.Cool Color Concrete Tile
Less expensive than slate and clay in most cases, but more costly than traditional shingles, concrete tile is an option for warm weather durability. Concrete is heavy and takes a long time to heat, making it a good material for warm weather roofing. Using poured concrete slab roofing is a low-cost option in many developing countries, as it provides protection from bad weather and pests. It does the same in more developed countries, acting as a barrier layer underneath more cosmetic roof treatments.
In its tile form, concrete is still heavy but is easier to install than the poured concrete. It is fireproof and solid, though porous enough to take in color when dyed. Using specialized "cool colors" will increase the energy efficiency of concrete tiling by reflecting more of the sun's rays than a roof treatment in standard dark colors.
Sand, water and cement make up concrete tiling, but the baking process toughens the material so it can withstand rain, heat and wind. Some concrete tile roofs in Europe and elsewhere have passed the 150-year-old mark and still cover and cool as originally designed.Installers of concrete tile should consult minimum code requirements for environmental conditions by region.In Orissa, for instance, securing tiles to meet hurricane-force wind resistance requirements involves some extra steps and precautions. "Batten down the hatches," as they say.
5.Green/Living roofs
Concentrations of dark asphalt roofs, parking lots and roadways in dense areas, especially in large cities, create a negative environmental effect called a "heat island effect" or "urban heat island effect." Heat soaks into these areas because of the dark materials that hold energy throughout the day and night.
Painting rooftops and roads white is one step toward reducing the amount of electricity and time needed to cool these urban hot spots, but another idea is to green the spaces from the tops down. Green or living roofs incorporate a waterproof membrane filled with soil and vegetation intended to cool naturally through soil temperature and growth of greenery. Roofs made of living plants also release oxygen into the air, making it less toxic and harmful than row upon row of petroleum-based shingles atop paved streets. Water runoff also serves to cool the buildings, and the entire system protects the base roofing underneath, adding to roof longevity.
Higher costs and lack of expertise and vision are likely to slow the growth of green roofing. Greenery topped buildings have been keeping buildings cool for decades in modern Europe, and Germany is the first and only country to publish a green roofing guide. But implementing the techniques on a large scale is years away
1 comment:
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