Cooler, Greener Roofs

Some roofs are made of recycled or recyclable materials, like rubber or plastics, but the greenness of a roof has little to do with its raw materials. In fact, any green benefits you pick up from recyclability are outweighed by the key role roofs play in a building’s thermal envelope. Here’s why: Americans spend about $40 billion each year to air condition buildings, fully one-sixth of all U.S. energy, according to the U.S. Environmental Protection Agency. That figure can be reduced substantially by simply changing the color of a roof. It can be reduced even further by using reflective roof materials or materials that frustrate the transfer of absorbed heat into the structure.

Roof-science Basics

You couldn’t build a more efficient solar collector than a black roof, yet they’re popular because Americans hate the look of white roofs. The consequence of the fashionable black roof is it reflects just 5 percent of the sun’s heat; the rest is absorbed. A gray roof reflects about 20 percent of the sun’s heat and absorbs the rest. However, white roofs reflect 25 percent. As a result, black roofs get as much as 90 degrees hotter than white roofs. Imagine reducing that $40 billion cooling bill by 25 percent just by changing the color, coating types and the resulting reflectivity of the roof material.

How can changing the features of just one roof have an effect on a national scale? If the building community buys into the cool-roof movement, it means changing not just one rooftop, but potentially hundreds of square miles of roofs. All these roofs currently are collecting solar energy and transferring it into structures, which then are forced to be cooled by gas-fired AC units or by using electricity, most of which comes from nuclear or coal sources that negatively impact the environment.

Roofing Ideas

An innovative solution has emerged that allows homeowners to have fashionable black roofs that reflect the sun’s heat like white roofs. Roof shingles now are being manufactured in lighter colors and/or with surface treatments that better reflect and emit heat. Granules embedded in the shingles appear dark, yet are highly reflective.

Although it’s odd to see an Energy Star label on squares of shingles because they don’t actually consume power, shingles affect power consumption so dramatically they can earn Energy Star status. An Energy Star shingle will have, upon installation, a solar reflectance greater than or equal to 0.25, meaning 25 percent of the sun’s heat is reflected. If you are installing metal roofs, you’ll find a wide range of Energy Star-rated products because metal roofs can be factory-treated with durable, highly reflective coatings. In fact, the vast majority of Energy Star-rated roofs are factory-treated metal roofs.

The Cool Roof Rating Council, or CRRC, offers another cool-roof product label. CRRC is the rating system followed by California’s Title 24—the mandated

energy-efficiency building standard. However, CRRC is not strictly a California program. This group tests roofing material and rates solar reflectance (a measure of what percent of the sun’s energy gets reflected by the roof) and solar emittance (a measure of how well the roof defeats transfer of that absorbed heat into the structure) to create a CRRC rating between 0 and 1. The higher the number, the better. Generally, roofs that are considered cool have ratings in the 0.7 to 0.75 range. View CRRC-rated products at coolroofs.org.

Recyclability

Although the color of a roof can make a big difference, recyclability still plays a role in determining a roof’s green attributes. Metal roofs are made entirely of recyclable material; even brand-new metal roofs can have 100 percent recycled content. High-tech EPDM rubber and TPO plastic are used to create molded, lightweight, shake- or slate-like shingles that offer long warranties, impact resistance and UL Class A fire ratings. Many of these new roofing products are made from 100 percent recycled content, and they are 100 percent recyclable.

For those readers who still think green building means using exotic or expensive products, think again. A simple adjustment to the attributes of the lowly roof shingle can have a dramatic and long-term effect on a structure’s energy consumption.

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