APRIL 2011

Recycled steel use growing with energy efficient buildings Click to Enlarge
E-mail the author

Everyone in the recycling industry is aware of the many benefits of recycled steel. It’s less expensive and more environmentally sound than drawing materials from nature, and its recyclability virtually endless.

A basic North American oxygen furnace uses anywhere from 25 to 35 percent recycled steel to make new flat-rolled steel used in products such as automotive fenders and appliances, cans, metal roofing and numerous other thin-gauge applications. The electric arc furnace uses more than 80 percent recycled steel to make new beams, plate, rebar and other structural and flat-rolled products. Most new steel products, including their original recycled content, will eventually feed back into the recycling stream.

Recycled steel has always been important in construction, but now it is finding new roles in structural applications as it helps improve energy efficiencies in commercial buildings and housing, becoming a high national priority for green buildings that seek to conserve resources and contribute to energy savings. On a smaller scale, this also applies to metals such as copper, aluminum and zinc, which are also recycled into new building materials.

In February, during his Penn State University speech, President Obama called for businesses to improve energy efficiency in commercial buildings across the United States. 

The recycled content of a metal roof is much greater than that in an asphalt roof.

Responding to the speech, Lawrence W. Kavanagh, president of the Steel Market Development Institute said, “The President has laid out an aggressive plan for retrofitting commercial buildings with energy-efficient upgrades. We can help businesses meet this challenge with steel technologies and products that are durable, cost-effective, provide long-term energy savings, and are available now.”

Whether doing retrofits or new construction, architects and engineers are using more steel in buildings, not just for energy savings, but to minimize maintenance costs and increase the life expectancy of buildings, satisfying sustainability objectives.

Cooler steel

A major developing trend is greater use of “cool” metal roofing and wall products that help reduce building energy consumption by lowering cooling loads. Many of these newer metal roofing materials are coated with paints containing infrared pigments that increase solar reflectivity and thermal emissivity, saving significantly on energy costs for cooling. Reflectivity is essentially bouncing solar energy back into the sky rather than let it penetrate the building. Emissivity is the ability of a surface to reduce heat build-up by re-emitting energy into the sky not as heat, but as light.

“The reflective technology is relatively new, having emerged over the past decade or so, but it’s just now reaching more broadly into the marketplace thanks to all the emphasis on energy efficiency. Thus the sale of metal roofing keeps going up,” said Greg Crawford, executive director of the Steel Recycling Institute and as executive director of the Cool Metal Roofing Coalition. “Unpainted Galvalumn (a 55 percent sheet steel product coated with aluminum and zinc) in many applications can be considered a cool metal roof because of its excellent reflectivity. Even cooler is the painted steel roof with infrared reflective pigments in the painting system. It not only provides a metal roof with very reflective properties, but it also has greatly improved emissivity that throws off heat.”

As reported by Lawrence Berkeley National Laboratory, installation of reflective metal roofing can save up to 40 percent in cooling energy costs. At the same time, highly emissive metal roofs can reduce urban air temperatures by as much as 12°F, helping to mitigate the “heat island effect” where the density of building in an urban area raises temperatures.

A basic, unpainted galvanized metal roof will reflect much of the solar radiation usually absorbed in a home under an asphalt roof. Homes in warmer climates, with pre-painted reflective metal roofing systems not only reflect solar energy but also cool the home by re-emitting most of the solar radiation captured temporarily on the roof surface. Where annual cooling loads dominate, a highly reflective and highly emissive painted or granular-coated metal roof is optimal for reducing energy consumption and can actually re-emit up to 90 percent of absorbed solar radiation.

“Generally, the reflectivity of asphalt roofing is low on the average of 20 percent or less and it gets lower, the darker color the roof. While it does not reflect well it has good emissive qualities. Metal roofing is going to be more expensive, maybe twice as expensive for a given job. However, the big trade off is the long, credible service life of a metal roof on the order of 30 to 35 years, including the superior energy savings potential over that time,” said Crawford.

Most metal roofing can be installed directly over asphalt shingles or membranes. In new construction and retrofits, green-conscious architects and builders are installing metal roofs with above sheathing ventilation (ASV), which can contribute up to a 30 percent additional reduction in heat gain through the roof. Crawford explained: “With ASV you install bats oriented up and down the roof and put the metal roofing on top of the bats to create an air vent of about one inch. As we all know, heat rises. As the roof heats up during the day, the heat in the air gap rises and automatically vents out the ridge. This reduces heat that could potentially go into the structure’s envelope. In winter, the air space is still and actually acts as an additional insulating layer.”

A metal roof can also offer additional protection compared to asphalt roofing from assaults from nature and can potentially reduce insurance costs. “Whether it’s worries about fires, hail storms, hurricanes, or other such events, we say that properly installed metal roofing is about as good as you are going to get. In California, homeowners who had metal roofs fared much better amid the wildfires. You can find stunning examples where fires simply skipped over them,” Crawford noted.

“We think market share for metal residential roofs in the United States is right around nine percent according to annual surveys by McGraw-Hill Analytics. Over the last 10 years, it’s grown from about 3 percent,” said Tom Black, executive director of the Metal Roofing Alliance, a group of contractors, manufacturers and suppliers of investment grade roofing. “These numbers include new construction as well as re-roofs, but by far the largest portion, 90 percent of the metal installed each year, is for re-roofing.”

Black continued, “For new construction a developer or builder is going to put the money into square footage, or the kitchen, something that sells the house rather than put money into the roof. But in a re-roof, it’s the consumer and the contractor making the decision. They are looking for long-term value, wanting to make it the last time that they have to deal with the roof. They are also considering weather events, especially in the Midwest where metal roofing stands up really well to devastating hail storms. Depending on where you are in the Midwest you can get discounts on your homeowners insurance, up to 35 percent in some areas of Texas. It depends on the insurance companies. I like to use a range of 20 to 25 percent discounts on average.”

Solid solar power platforms

As more homebuilders and commercial real estate developers include rooftop solar generation, metal roofing has become the preferred foundation for heavy photovoltaic panel arrays. Metal roofing can be expected to last longer than the solar panels themselves, which are typically performance warranted for 25 years. Panels can actually have productive lives of 35 to 40 years. It makes little sense to install solar panels on a membrane roof with a lifespan of 15 to 20 years because when the roof has to be replaced the panels have to be disconnected, removed and reinstalled at great expense. A solar module can be installed on a metal roof with a simple attachment that does not penetrate the roof, making panel swaps easy.

Metal roofing and walls are also ideally suited to the new breed of thin-film solar cells that are growing in popularity because of lower production costs than traditional polysilicon panels. These thin-film laminates are a lightweight, flexible, and a durable alternative to conventional glass-faced photovoltaic arrays that many people find unsightly. Not only more aesthetically pleasing than PV modules, thin-film silicon solar laminates can be applied between the seams on existing metal roofs and siding or laminated onto new building materials. Thin-film silicon solar has come a long way over the past few decades and now represents approximately 20 percent of all solar cells being manufactured today.

In the near future, emerging nanocrystal and dye-sensitive solar cell technologies with micron-thin layers may be deposited or printed on metal substrates. This holds the promise to truly revolutionize the function of metal building materials by adding a cheap, distributed source of electricity generation.

Aesthetic challenges

Consumer perceptions have been largely clouded by the old fashioned galvanized roofs long used on farm and commercial buildings which have shown unsightly rusting after decades in service, even though they maintained their waterproofing. They fail to recognize the good economics of installation costs versus length of service, nor the new advances that have been made in metal roofing and siding technology.

Today, metal roofing and side panels are fabricated from steel and alloys to mimic most every other type of building material and are available in virtually every profile, finish and color. Lighter colors offer the best reflectivity and emissivity, therefore better energy performance. In appearance, metal roofing systems are designed to be indistinguishable from typical roofing materials. Factory produced products with infrared pigment coatings are self-cleaning with normal rain. Smooth surfaces make it difficult for dirt and algae to build up, which maintains a cleaner surface and optimizes the reflectivity and emissivity characteristics.

Earning green points

Because of high recycled content and the ultimate recyclability of the material as well as energy efficiency factors, cool metal building products can help contribute towards points under the U.S. Green Building Council Leadership in Energy and Environmental Design (LEED) green building rating system.

Architects, real estate professionals, engineers, builders, lenders government officials are looking to acquire LEED points for a given award level, such as Gold, but essentially the design can be seen as adding value to a property. LEED rated homes and commercial buildings are becoming the new standard in green excellence.

“There is a federal tax rebate for painted cool metal roofs, but it must meet the Energy Star requirements to qualify. It’s 10 percent of the material cost or a maximum of $500,” said Black.

Green is good for the environment, but the real green is in the dollars saved by using recycled and recyclable metals in building materials, not just because it rightfully conserves resources, but because well performing metal construction products are also stronger and more durable and thus, all the way around, a better investment in the long run.