Energy, Green Building—and Metal Panels

It's just another reason why—according to the Metal Construction Association—“Metal is one of the most energy-efficient and sustainable building materials available.”

A Metal Initiative white paper, Improving Building Energy Efficiency with Metal Roofs and Walls points out for example, that “cool metal roofing is a viable solution that offers enormous economic and environmental benefits. It conserves utility use by helping to cool buildings naturally in warmer climates and temperatures.” That paper goes on to show how “the same paint systems used for cool roof systems are used for metal wall systems and these energy-efficient wall systems are beginning to gain more visibility in the market.”

Insulated metal panels are also an energy-efficient choice for architects who need to consider the multitude of efficiency-related measures when designing buildings with metal exteriors—specifically, thermal performance and insulation integrity as measured in R-value and U-value or U-factor ratings. “While R-value measures resistance to heat transfer, U-value measures the rate of heat transfer,” according to Ken Brenden, AAMA technical services manager, who covered the subject in a recent Metal Construction News article comparing metal walls in terms of the panel construction and core characteristics.

In general, Brenden concluded, IMPs offer “extremely high R-values.” IMPs also offer the benefits of continuous insulation and serve as continuous air barriers. Still, in choosing metal products, architects should review the three types of panels—single-skin panels, insulated metal panels (IMPs), and metal composite materials (MCMs)—to understand which will perform best given the design specifications and intended use of a given building. In the Whole Building Design Guide article “Building Envelope Design Guide – Panelized Metal Wall Systems,” the authors note, “The designer must select the types of metal panels that will meet design criteria and also establish the panel performance criteria.” That is, architects need to weigh performance against aesthetics.

The MCA's Selection Guide for Insulated Metal Panels indicates that, “the primary variable in the selection of an insulated panel is the thickness needed to meet the required thermal value. After the thermal value is determined, a review of the structural span tables is necessary to ensure that the panels in the thickness selected will meet the structural requirements.”

While single-skin panels and MCMs provide no significant thermal resistance and rely on the insulation included in backing systems, IMPs provide an R-value of roughly R7 per inch of thickness, thanks to the solidity of their foam cores, which retain their rigid uniformity and don't suffer from compression as some insulation types do, which can significantly reduce R-value. The insulation in IMPs is commonly injected as a urethane foam—again, typically polyurethane or polyisocyanurate—between two continuous metal sheets, called coils, and then allowed to expand and bond to those metal surfaces. Some manufacturers use a laminating process to bond foam board to the metal faces.

The MCA literature also explains that IMPs “have a foam core that provides R-values generally ranging from 7 to 48 … in thickness from 1 inch to 6 inches for wall systems, and R-values ranging from 10 to 48 for roof systems.” Because the insulation in IMPs is enclosed between two metal skins, it isn't subject to significant thermal drift—caused by offgassing—which can decrease R-values. Likewise, the continuous insulation within the sandwich design of IMPs reduces thermal bridging, which occurs when conductive materials allow heat to travel. To further reduce thermal bridging, industry experts suggest keeping the numbers of fasteners and joints in a given design to a minimum.

Because they can be custom-fabricated to meet the architect's design criteria, IMPs interact and interface as desired with other building materials and fenestration. According to Paul E. Totten, senior principal at Halsall Associates, if insulated metal panels are employed in an enclosure design, “the insulating cladding can be aligned with the windows to maintain continuity,”³ as reviewed in the NIBS paper he co-authored, The Effects of Thermal Bridging at Interface Conditions.

Also, while metal wall- and roof-panel products are available in a wide variety of shapes, sizes, colors, and textures, it's important to design the mechanical connections properly and for contractors to use the proper hardware and fastening tools during the installation process. Industry leaders from metal panel companies urge architects and installers to make sure the products they choose are designed for mutual use, as incompatible products can undermine envelope performance. The keys to proper façade detailing for IMPs include compatibility of the fasteners and the IMP substrate. Among the potential defects is corrosion between dissimilar metal types, including the destructive electrochemical process known as galvanic corrosion. Experts caution: If the architect is not following manufacturer guidelines for hardware and panel joinery, make sure to have an expert review the proposed design in the earliest possible phase.

When installed properly, one significant benefit offered by IMPs is their rigid insulating cores, which prevent thermal bridging. Similarly, the seals at panel edges, where they interlock, provide thermal breaks within a cladding system.

This raises a valuable point: Choosing panelized metal products for building exteriors can be an overall win with respect to sustainability. MCA lists a number of considerations: “Today's metal construction products,” says the group, “contain 25 percent to 95 percent recycled materials [and] are virtually 100 percent recyclable.” Industry professionals say that metal wall- and roof-panel products should last at least 40 years, with well-maintained energy savings over that lifespan.

Beyond those direct sustainability benefits, manufacturers point out that the comparatively lightweight nature of their products means cost-savings for transport, delivery and construction operations. Lighter weight also means that a building's foundation and structural framing loads are decreased as compared to heavier façade materials. The fact's that metal wall- and roof-panel systems can be installed in inclement weather conditions, which means uninterrupted installation, and require no significant maintenance mean even greater potential cost savings.

As reported in the Whole Building Design Guide article Building Envelope Design Guide —Panelized Metal Wall Systems, “metal panel systems, when properly designed and constructed, require little maintenance. However, over the life of the structure cleaning and sealant stet may be required. If the system includes sealant, the time frame for sealant replacement usually ranges from seven to over 20-year periods, depending on the sealant used and the joint design.”

Continuous product improvements in the industry make metal wall- and roof-panel systems an ideal choice for architects and end-users looking for aesthetic flexibility and energy-efficient building solutions. These developments place manufacturers in a good position to meet sustainability-geared performance requirements and client expectations. The use of metal-panel systems can earn architects credit toward LEED certification.