Contrarian Micro Textures has announced their findings relating to research they conducted on solar reflectance that has determined stainless steel roofs can provide a significant reduction in global warming. Further, the sustainably efficient solar reflectance of stainless steel, combined with its very low emission of infrared energy, create more energy efficient buildings. While it is theoretically possible to offset global warming completely by roofing enough buildings in stainless steel, the real solution to the problem would include further conservation measures as well. The point being that stainless steel roofs offer a meaningful contribution towards cooling the planet.
Stainless steel is an extraordinarily efficient reflector of solar radiation, making it an ideal material for building construction, particularly roofing. While initial solar reflectance of white painted metal surfaces can achieve the same degree of reflectance as stainless steel, painted surfaces lose up to 5% of their solar reflectance each year, due to oxidation. An oxidized surface tends to convert solar energy to infrared energy, which heats up the atmosphere. Since stainless steel does not oxidize, it retains its solar reflectance efficiency over time. Therefore stainless steel provides a much greater offset to global warming in the long run compared to white painted metals or membrane products that degrade over time. Beyond effectively cooling the planet, stainless steel roofs and wall systems conserve energy. In fact, stainless steel contributes an insulation value to an exterior cladding system.
During daylight hours the Sun bombards the Earth with solar radiation, averaging 395 Watts per meter squared for 85% of the planet. About a third of this radiation is reflected by the Earth’s surface. The remainder gets converted to infrared energy (heat), which gets absorbed and re-emitted by greenhouse gases. The effect of this is to warm the surface and the troposphere of the Earth. The physics here is pretty simple, carbon in the atmosphere, whether it’s generated naturally by the Earth or by man-made means, serves to trap infrared energy. If we are able to generate less heat through energy conservation, improvement in the global warming phenomenon can be achieved. However, conservation alone cannot solve the problem. We must rely on reflective materials to make a substantial contribution in order to completely offset global warming.
Any human who dresses for a hot sunny day will prefer a white shirt to a black one in order to be comfortable. We offer another example of a natural species on the Earth that has adapted to living in a region of the earth where solar radiation is intense. Clad in a reflective skin, the Saharan Silver Ant is able to function effectively in the midday sun. Other species are unable to operate in full vigor during full sunlight, but this creature manages to reflect solar radiation very efficiently. Building design professionals can take a lesson from the Saharan Silver Ant in creating buildings that are likewise not reactive to the midday sun. The world will be cooler if buildings are clad in sustainably reflective materials like stainless steel.
Stainless steel reflects substantially more solar energy without converting to infrared (heat) than asphalt or white painted metal. In fact, stainless steel absorbs only 8 Watts per meter squared (about 3% of total radiation) of infrared energy compared to 46 Watts per meter squared in the case of aged white painted metal and a whopping 122 Watts in the case of asphalt.
It’s important to point out that much of the burden of the solution of reflective materials to curb global warming lies in latitudes nearer to the equator, as the angle of the Sun creates both a greater impact and a greater opportunity for effective remediation. When you consider the world’s population growth and wealth generation is skewed toward countries near the equator, a large part of the burden as well as the opportunity to achieve global cooling lies between the 45th parallels North and South. It is interesting to note that if 2,000 square feet of stainless steel roofing were installed for each person on Earth, global warming would be offset completely. Highlighting the areas of Texas and Burma combined, which represent the portion of the Earth that would need to be covered in stainless steel to neutralize global warming, it is not realistic to build giant canopies over these regions no more than it is realistic to build 2,000 square feet of roofing per person. Clearly, a solution to global warming is within reach by maximizing the use of highly reflective building materials like stainless steel combined with effective conservation measures.
Because of its very low emissivity, stainless steel makes a contribution in the area of conservation as well. Assuming outside temperature of 40°C (104°F) and maintaining an interior building temperature of 20°C (68°F), half the insulation of white painted metal and a third of the insulation of asphalt is required to maintain a heat loss of 10 Watts per meter squared in the case of stainless steel. With stainless steel building panels, the owner has two very good choices. The first is to accept good performance with less insulation and therefore save expenses related to acquiring it and providing space to install it. The second, and perhaps better choice is to detail a building that is even more energy efficient using standard insulation details that are used with more common materials.
A real world example of a stainless steel roof saving energy can be found at the David Lawrence Convention Center in Pittsburgh, PA. While stainless steel was originally chosen for its durability, high recycled content and high recyclability, it stands to reason that the stainless steel roof has contributed to energy savings as well. In fact, the DLCC upgraded the building’s LEED® status from Silver to Gold, due in part to lower than expected energy consumption in the 15 – 20% range. While an engineering study concluded a natural ventilation system has been the major contributor to the building’s energy efficiency, Contrarian’s later research suggests a meaningful contribution from the stainless steel roof itself. Solar reflectance readings taken on the DLCC roof 10 years after installation, with no cleaning having ever been conducted, showed no degradation compared to a cleaned roof specimen or a new control sample. The dirt resistant InvariMatte® finish was deemed to be a factor in maintaining the roof’s energy efficiency.
Stainless steel is an undervalued building material that provides significant benefits to the building owner and represents a substantial weapon in the battle against global warming. Beyond its impressive energy performance, as a building material, stainless steel has low embodied energy compared to other construction materials including glass, carbon steel, and aluminum. Stainless steel contains at least 60% recycled content and is 100% recyclable without having to downgrade to less critical applications. Stainless steel building panels are resistant to fire, wind, hail, and corrosion. Because of its extraordinary durability and corrosion resistance, stainless steel buildings can last indefinitely, assuring low maintenance cost and a long service life.