eBook - Energy Saving Home Improvements from A to Z

Roofing Coatings

The sun's energy inevitably finds its way into the buildings on which it falls. In the summertime, this unwanted heat energy makes buildings hot and requires more air-conditioning. Since the summertime sun rises high in the sky, the sun's radiant energy falls mainly on the roof, with east and west walls of buildings also receiving a significant share.

One of the simplest ways to keep solar heat out of buildings is to use reflective roofing materials. Then, the sun's radiant energy is simply reflected back toward the sky from which it came. In fact, reflective materials also help keep the building's environment (i.e., the city) cool, by reflecting solar energy back out into space, thereby reducing the heat island effect. The Cool Roofing Materials Database provides information about the reflective properties of different roofing materials. Look for ENERGY STAR labeled roofing products, they reflect heat and can reduce peak cooling demand by 10% to 15%.

Another way to lower cooling costs and extend roof life is to put a light colored coating (also called cool-coating system) over an existing roof. Adding a cool coating is most beneficial for a building that meets these criteria:

• Is in a climate with hot, sunny weather during at least part of the year

• Uses significant cooling energy and/or has problems maintaining comfort

• Has a large roof area compared to the rest of the building's surface area

• Has roofing which tends to crack and age prematurely from sun damage

Just as wearing white clothes reflects the sun's heat from your body, a white or light-colored roof will help reflect the sun's heat away from your home. This strategy works particularly well when trees are located next to the reflecting surface. Not only does the tree provide shade, it absorbs the reflected sunlight for photosynthesis. In the process, water evaporates from the tree, cooling the air around the house.

Roofs play a key role in protecting building occupants and interiors from outside weather conditions, primarily moisture. The roof, insulation, and ventilation must all work together to keep the building free of moisture. Roofs also provide protection from the sun. In fact, if designed correctly, roof overhangs can protect the buildings exterior walls from moisture and sun. (See passive solar design.)

Different roof designs and materials are used for residential and commercial buildings. Commercial buildings typically use low-slope or flat roofs, while home roofs are sloped. The concerns regarding moisture, standing water, durability and appearance are different, reflected in the choices of roofing materials.

Roof design can impact the building's thermal performance. For example, in a metal-framed building, the metal eaves can act as thermal fins, moving heat out of the building, which is not desirable in heating climates.

A number of roofing choices are available for high-performance buildings. New roof shingles on the market today even produce electricity using solar technology. Reflective roofing materials or coatings help send the heat back into the sky rather than into the building. And recycled content shingles are available that look like slate or wood. Roofing materials should be integrated into the building's whole-building design.

• A number of roofing materials are available:

• Asphalt

• Metal

• Wood

• Concrete and Tile

• Single-Ply

• Recycled Content

• Solar Shingles

• Aluminum

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