This course is part of the Metal Architecture Academy

Cradle-to-cradle design is an idea that uses nature’s processes as a model for the built environment, including its products and systems. Whereas the idea of cradle to grave restricts focus on a product or system from birth to death, cradle-to-cradle encourages a more holistic approach in which the architecture, engineering, and construction industry is sustainable and considerate of its impacts from one generation to the next.

Specifying metal roofs and walls for a cradle-to-cradle design would include considering the sustainability characteristics featuring energy efficiency, recyclability, and durability. Considering how to optimize these traits for a building’s location and function promises that a project is serving that cradle-to-cradle approach. Seeking out the right products can assist a project in meeting requirements of Cradle to Cradle (C2C) and the Leadership in Energy and Environmental Design (LEED) green building rating system. In addition, these sustainability goals within the cradle-to-cradle approach often support health, safety, and wellness goals—which makes sense because the idea is about building spaces that model on nature’s ecosystems.

When specifying for metal roofs and walls, there are a few ways to obtain verifiable product performance information. Key to transparency and product performance assurance are independent, third-party labels, evaluations, and program certifications such as UL GREENGUARD Gold and Declare and product reports such as Environmental Product Declarations (EPDs) and Health Product Declarations (HPDs). These third-party evaluations provide assurance, credibility, and verification that manufacturers themselves cannot provide, and they are the path toward certified buildings.

Life-Cycle Assessments

A life-cycle assessment or analysis (LCA) is one way that products are assessed for sustainability. It is a type of environmental accounting commonly used for assessing environmental impacts associated with all stages of a commercial product, process, or service’s life cycle. When applied to multiple assemblies at the building level, it is referred to as a Whole Building Life-Cycle Assessment (WBLCA). Green building rating systems such as LEED and Envision include credits for performing WBLCA and choosing less impactful materials and systems. This is a cradle-to-grave assessment that can be used in the broader goal of a cradle-to-cradle approach.

In a whole building LCA study by Houston-based Walter P. Moore Associates on behalf of the Metal Building Manufacturers Association, the environmental impact of metal buildings was found to be lower in case studies comparing structural and envelope materials to load-bearing concrete, masonry, tilt-up, and steel-framed construction within the same basic building footprint. The study concluded that in buildings where metal is typically most economical, LCA performance is also better, with the least embodied building material impact.

EPDs and HPDs

An Environmental Product Declaration (EPD) report summarizes the life-cycle impact of a product from “cradle to grave” based on a product’s LCA. An EPD report includes information about a product’s global warming potential, its potential toxicity, and manufacturer’s sustainability initiatives, among other things. EPDs do not rank products. Instead, an EPD is a transparency tool that helps specifiers make choices based on the sustainable qualities and environmental impacts. Products with EPDs can contribute to LEED and WELL credits.

A Health Product Declaration (HPD) is similar to an EPD but is focused on the health impacts of the product. HPDs are shared by manufacturers to disclose a product’s ingredients and any health hazards associated with these ingredients. HPDs may be created by product manufacturers, by manufacturer’s agent, or by a third party. As with EPDs, an HPD is a transparency document that allows a specifier or building owner to compare the health impacts of products using a standardized format. Products with HPDs can also contribute to both LEED and WELL credits. Third-party verified contributes more than self-verified products.

With the concept of sustainability now being widely embraced by the architectural community, metal roofs and walls are being seen in a new light. Metal roofing can contribute significantly to the sustainable building movement. Their high recycled content, total recyclability, energy efficiency, and the ability to utilize “cool” finishes allow "cool metal roofs" to qualify for LEED points.

Photo courtesy of Northclad

The content of steel, aluminum, and copper metal roofing and wall material contains substantial amounts of recycled materials, making them excellent candidates for LEED credits.

Recyclability

While the most widely known LEED credit for roofing is for the heat island effect, metal’s high recycled content, total recyclability, and smooth, impervious surface allow metal to meet requirements for other points in the LEED program as well.

Metal is the world’s most recycled material. Iron, including its refined product steel, is the most widely used of all the metals, and the recycling of iron and steel scrap (ferrous scrap) is an important activity worldwide. Because it is economically advantageous to recycle iron and steel by remelting and casting for use in the manufacture of new steel products, a significant industry has developed to collect old scrap, including used and obsolete iron and steel products, and new ferrous scrap generated in steel mills and steel-product manufacturing plants. The North American steel industry’s overall recycling rate is 71%, according to the Steel Recycling Institute.

Consequently, the content of steel, aluminum, and copper metal roofing material is comprised of substantial amounts of recycled materials, making them excellent candidates to be considered for the LEED credits focused on Materials and Resources.

Most steel sheet products are produced through the basic oxygen furnace process, which uses 25%–35% old steel to make new steel. Figures for pre-consumer and post-consumer recycled scrap may vary slightly at individual furnaces making steel around the country. And architects and builders will certainly want to ask their metal panel supplier to provide them with their product’s recycled content.

Aluminum is recycled extensively from both post-consumer and pre-consumer sources. According to the Aluminum Association, the recycled content of domestically produced, flat-rolled products for the building and construction market is approximately 80%–85%. Aluminum Alloy 3105, the aluminum product used in nearly every aluminum standing seam roofing application, is produced from 99% scrap, 80% of which is from post-consumer sources. The aluminum coil used comes from state-of-the-art, scrap-based aluminum mini-mills producing a variety of common alloy sheets. The association notes that, in addition, at the end of its long, useful life, aluminum roofing can be repeatedly recycled back into similar products with no loss of quality.

Copper is a routinely recycled metal with the highest scrap value of any building metal. Copper’s high cost makes it a favored product for collection and sale to nonferrous scrap-recycling companies. The average recycled content of all copper products is 44.6%. Copper roofing and wall cladding contains 75% scrap. Almost 50% of this is post-consumer scrap.

How do metal roofing and wall cladding manufacturers gain LEED compliancy? It must be made clear that the U.S. Green Building Council does not certify products, but only buildings, in the LEED program. However, a product’s sustainable attributes can help earn credits and points toward a building’s LEED certification.

Documentation and Other Challenges

Trying to track down material resources including the substrate manufacturer's information on recycled content or location of manufacture can be challenging. Some metal panel manufacturers who have been working with LEED projects and architects are aware of this need and have the information, including letters and other forms of verification from substrate manufacturers. It is important that for projects pursuing LEED certification, that specifications and bid packages provide clear directions about points of origin of the metal and manufacturer distance requirements (for example, 100 miles or less from the project site), and for recycled content requirements.

Metal panels may play an indirect role in qualifying for other LEED credits as well. Ultimately, metal panels present architects and builders with an opportunity to use the products’ sustainable attributes in a LEED project. When amassed with other rating points for various sustainable features, metal can be a simple and cost-effective way to meet program requirements.

THERMAL AND ENERGY-SAVING BENEFITS OF METAL

Metal provides many thermal and energy-saving benefits. This section looks at all the ways metal provides energy-saving benefits to a project by way of reflective pigment technology that results in overall energy efficiency and lowers utility bills. There are a variety of coatings that can keep metal cool in the summer and warm in the winter. These energy saving benefits are not just environmental solutions; they provide health, safety, and well-being to occupants in the space. Thermal qualities ensure the comfort of occupants.

Cool roofs can reduce heat transfer to the indoor environment, thereby lowering air conditioning costs. Studies monitoring buildings in California and Florida demonstrate that cool roofs save residents and building owners 20–70% in annual cooling energy use, and cool metal roofing can qualify for tax incentives and earn LEED credits.

Photo courtesy of Tedlar

Cool roofs, like this one at an oceanfront Hilton, can reduce the heat island effect, lower air conditioning costs, and minimize negative impact on microclimate and human and wildlife habitat.

Cool roofs can also reduce thermal gradient differences between developed and undeveloped areas to minimize impact on microclimate and human and wildlife habitat.

The temperatures in the air above heat islands can be as much as 12 degrees Fahrenheit hotter than the surrounding suburbs, leading to higher air conditioning costs, greater use of electricity, and higher levels of smog and ozone.

The U.S. Department of Energy research has shown that one additional percent of reflectivity in a roof coating on average will reduce the roof temperature by one degree. The ultimate result is that heat is reflected away from buildings, smog is reduced, energy costs are lowered, and the life expectancy of the roof will be increased due to less expansion and contraction.

Cool roofs reflect heat well across the entire solar spectrum, especially in the infrared and visible wavelengths. In addition to absorbing less heat, the coolest roofing materials radiate away any absorbed heat.

Regardless of the kind of material used, cool roofs have two important surface properties: a high solar reflectance and a high thermal emittance. Solar reflectance, also called albedo, is a measure of the ability of a surface material to reflect sunlight—including the visible, infrared, and ultraviolet wavelengths—on a scale of 0 to 1, which can be expressed as a decimal fraction (0.7) or a percentage (70%). Essentially, it is the percentage of solar energy that is reflected by a surface.

Thermal emittance is defined as the percentage of energy a material can radiate away after it is absorbed. It is the ability to release absorbed heat. Scientists use a number between 0 and 1 (or a percentage) to express emittance.

Solar reflectance and thermal emittance have noticeable effects on temperature. Some conventional roof surfaces have low reflectance (from 5%–25%) and high thermal emittance (typically over 80%). These surfaces can heat up to 150–190 degrees Fahrenheit at midday during the summer. Bare metal or metallic surfaced roofs often have a high solar reflectance (typically 50% or higher) and may have low thermal emittance (anywhere between 2% and 66%), depending on their surface treatment. These surfaces warm to 140–170 degrees Fahrenheit. Cool roofs with both high reflectance and high emittance warm to only 100–120 degrees Fahrenheit in the summer sun.

Under LEED v4, in the heat island reduction credit in the sustainable sites category, roofing materials used on low slope roofs with a slope of less than 2:12 must now meet a minimum initial solar reflectance index (SRI) of 82 (or a 3-year aged SRI of 64), while steep-sloped roofs with a slope of more than 2:12 must have a minimum SRI of 39 (or a 3-year aged SRI of 32).

According to these requirements, an SRI is defined as "a measure of the constructed surface's ability to reflect solar heat as shown by a small temperature rise. It is defined so that a standard black (reflectance of 0.05 and emittance of 0.90) is zero (0) while the SRI for a standard white (reflectance of 0.80 and emittance 0.90) is 100."

To calculate the SRI for a given material, it is necessary to obtain the reflectance and emittance values for the material. SRI is calculated according to ASTM E 1980. This is a standard practice for calculating the SRI of horizontal and low-sloped opaque surfaces with emissivity greater than 0.1. Reflectance is calculated according to any one of three ASTM standards—ASTM E 903, ASTM E 1918, or ASTM C 1549. Emittance is calculated according to ASTM E 408 or ASTM C 1371.