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Using Stainless Steel as a Building Envelope

Stainless steel is emerging as a material of choice in build-ing construction. Its longevity is without question. Recy-cling statistics are impressive. It has the lowest embodied energy of any metal used in construction. Finishing methods offer substantial variety. If this list of benefits isnt impressive enough, stainless steels unparalleled solar reflectance saves energy and reduces global warming.

While the majority of architectural applications of stainless steel have been for interior elements like elevators, the shift to-ward sustainable materials has propelled the use of stainless steel as a building envelope in recent years. As architects, spec-ifiers, fabricators and contractors become more familiar with the application of stainless steel in architecture, building owners will realize lower maintenance and operating costs through in-creased use of this sustainable material.

A building envelope is what separates the inside from the outside and its components include the foundation, the roof, the walls, the door and the windows. The materials used for these parts help determine the effectiveness, structural integrity and

durability of the building, which stated briefly means the way that the pieces interact with one another, their connections, their fasteners and fabrications. All these pieces and their details work in conjunction to provide physical protection from the weather, the indoor climate, the air quality, the durability and the energy efficiency.

Stainless steels use in building envelope applications dates as far back as the 1920s. Perhaps the most prominent building from that era is the Chrysler Building. Completed in 1930, the stainless work has withstood the test of time, with maintenance limited to two cleanings (one in 1961 and another in 1995) and the replacement in 1995 of a few panels near the heating ex-hausts that showed evidence of pitting corrosion. Clearly, the use of such a durable material has saved the owners of this building considerable expense over the years.

Another example of stainless steels durability is the Socony Mobil building, also in New York City. The accompanying photo shows a recent cleaning that was undertaken. Completed in the mid 1950s, the building accumulated dirt until cleaning was undertaken in 1995. This cleaning was accomplished with soap, water and cotton cloths. Ammonia was used to address some spots that did not respond to soap and water. The finish, being somewhat coarse, facilitated the buildup of dirt on the exterior surfaces but this condition did not prevent the appearance from being 100 percent restored with traditional cleaning methods.

These fine examples of stainless steel envelopes on histor-

James HallidayPresident, Contrarian Metal Resources

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ic buildings underscore what true sustainability is as stainless steel offers greater residual and resale value with lower main-tenance costs as it does not require repainting or resurfacing. While the use of stainless steel building envelopes was a bit of a novelty when these two New York properties were built, there has been increased interest in this impressive material in recent years.

With respect to the maintenance of stainless steel, when properly specified and installed it does not require replacement and therefore avoids service disruption which should not be un-dervalued. Stainless steel lasts indefinitely without coatings that emit volatile organic compounds (VOCs) as in the case of many painted surfaces. Stainless requires minimal maintenance and has no leaching or runoff as with less stable materials. World-wide, stainless steel is 60% recycled. In the United States the figure is 80%, it is a truly green, sustainable product that when used appropriately will garner LEED certification points. In ad-dition, when the building is no longer in service it is highly likely that the material will be recycled. The result is a sustainable de-sign with low maintenance costs and low environmental impact that generates long-term value to the building owner. Unlike aluminum, for example, stainless steel can be fully recycled into new stainless steel applications without needing to be downgraded. Further, the extraordinarily high recycled content of stainless steel is part of the reason why it has the lowest embodied ener-gy of metals used in construction.

Contrarian Metal Resources has developed a number of finishes that are specifically designed for architectural appli-cations. Its line of micro-embossed finishes in particular, provide reduced maintenance costs since they are hydrophobic, or self-cleaning. Available in stainless steel as well as titanium with

varying degrees of reflectivity, these finishes support a number of design aesthetics while delivering ease of maintenance. We suggest that the cleaning crew on the Sacony Mobil building would have had a better looking building start with an a much easier job on their hands in order to clean it if these products were available in the 1950s when it was built.

Contrarian Metal Resources signature product, InvariMatte Stainless Steel was specified for the new Hamid International Airport, Doha, Qatar. Its gulf location is a corrosive environment with elevated temperatures and sand-bearing winds that con-tribute to the severity of its environment. Contrarian worked in conjunction with ATI Flat Rolled, its melting mill supplier and Bemo USA, a leading international roofing concern, in order to meet the challenge by developing an ATI 2003 lean duplex alloy version of the InvariMatte finish that could be fabricated into a structural standing seam roofing system. The result is a hand-some roof that is low gloss, dirt resistant, uniformly textured and stands up nicely to the harsh environment in Doha. The oldest panels have been installed for more than 8 years with no signs of corrosion.

Beyond coastal Middle East environments, there are many other locations around the world where mild grades of stain-less steel do not have adequate corrosion resistance. Coastal India, other Asian locations and even parts of North America, such as the Hawaiian islands present environmental conditions where Type 316 stainless steel, the normal marine grade, can rust. The development of ATI 2003 InvariMatte stainless steel allows sustainable corrosion free performance of metal building envelopes in these locations at lower cost. Prior to its develop-ment, coatings and their resulting maintenance and replace-ment were the only metal building options, unless titanium could find its way into the budget.

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While the duplex alloy version of InvariMatte was designed for Doha with corrosion resistance and glare reduction in mind, much more was learned from this extraordinary project. Atop the Hamid airport roof on a 48 degree Celsius day in full sun, I was unable to detect radiant heat emanating from the roofs surface. I placed my hand on the metal and discovered to my surprise that the roof was comfortable to the touch. Clearly, something important was going on. When we returned to the United States, we initiated a study to try to understand why that roof was cool to the touch, and what it meant for the building owner. With the help of an independent metallurgical consultant, we obtained a number of important findings.

In short, we were able to understand the important solar reflectance property of stainless steel and what it means to en-ergy efficiency as well as global warming. We also became more aware of the potential human health risk of urban surfaces that generate heat from solar radiation. Beyond heat island mitigation for global warmings sake, stainless steel building envelopes

(better than even white painted surfaces) promise to reduce urban temperatures during heat waves, potentially saving lives. It was clear to us that a great deal can be done to benefit planet Earth through the increased use of stainless steel in construction.

Stainless steel is an extraordinarily efficient reflector of solar radiation, making it an ideal material for roofing as well as wall systems. Stainless steel does not oxidize; it retains its solar reflectance efficiency over time, unlike painted surfaces and membrane materials. While modern high-tech white paint finishes offer about the same solar reflectance when new, they oxidize over time, thereby losing solar reflectance. After about 20 years in most environments, white paint loses about a third of its solar reflectance, while InvariMatte stainless steel has been proven to lose none.

Accumulated dirt on the surface of a building envelope will interfere with solar reflection. This is true of any material, in-cluding stainless steel. Since InvariMatte is designed to shed dirt, its solar reflection efficiency is undisturbed over time. We tested three InvariMatte roofs in different parts of the United States after 10 years in service that had not been cleaned and were unable to measure any degradation in solar reflectance compared to brand-new control samples.

Beyond cooling the planet, stainless steel roofs and wall systems act as radiant barriers that conserve energy. Since stainless steel contributes to the buildings insulation system in this important way, the advantages apply to warm climates as well as cold. However, the biggest economic benefits as well as the greatest contribution to cooling the planet will be realized in hot climates.

In the past, stainless steel had been an underappreciated building material. However, more building owners and the con-struction professionals who serve them are recognizing the tre-mendous value this material represents. Beyond its impressive energy performance as a building material, stainless steel has low embodied energy compared to other construction materials including glass and painted aluminum. Provided the right alloy is used for a given environment, its durability is unquestioned, allowing stainless steel buildings to last indefinitely with low maintenance and operating costs over a service life that can last as long as the building stands.

BUILDING ENVELOPE