Key Codes and Standards for Metal Claddings

Other standards for IMPs and metal panels are focused on their manufacture, detailing, installation, erection and joinery. According to MBCI's Ken Buchinger, minimum performance standards are given primarily by a half-dozen groups, including: ASTM International; the American Architectural Manufacturer's Association (AAMA); the American Society of Civil Engineers (ASCE); ICC Evaluation Service (ICC-ES); and the International Accreditation Service (IAS), which has a certification program for inspecting metal building systems. Among the most important tests to consider are ASTM E1592 and E330, which test the structural performance of sheet-metal roof and siding systems or their fenestration systems, and ASTM E72, a strength test for panels to ensure proper performance in building construction.

ASCE 7 provides for minimum design loads, as is typical with any building design. AAMA's tests for structural loading, water penetration, and air and water resistance are very important for specifiers to include. Two related tests of weather resistance are AAMA 809.2—a spec for non-drying sealants—and AAMA 501.2, a water leakage check for glazed areas of panelized metal claddings, such as storefronts and sloped fenestration. Other AAMA standards seen in metal panel specifications include AAMA 621, for organic coatings applied to hot-dipped galvanized (HDG) and zinc-aluminum-treated steel.

Yet the ASTM standards are among the most pertinent specifically for metal cladding performance. For example, structural performance is given by the manufacturer's tests against ASTM E 72—a basic strength test for panels—as well as ASTM E 1592, an air-pressure method that addresses the robustness of sheet-metal roofing and siding assemblies.

The balance of the key ASTM International standards address parameters for energy performance as well as concerns of aesthetics and durability. Looks and resilience are related, of course: For example, ASTM A 755 describes the hot-dip process for metallic coating and prepainting by coil metal suppliers, while ASTM D 4214 presents the relative tendency of an exterior paint to chalk or flake. Other standards describe the minimum or required hot-dip techniques for applying protective zinc, zinc-iron, and aluminum-zinc coatings.

In terms of energy performance of metal panel claddings and IMP systems, there are four important standards that help support compliance with IECC, ASHRAE 90.1 and other jurisdictional energy codes. Understandably, they address some points of vulnerability:

• ASTM C920—Specification for Elastomeric Joint Sealants. Since the air leakage through metal skins is effectively zero, any joints and penetrations are critical control areas. In addition to gaskets and tapes, elastomeric sealants—typically with a backer rod or other backup material—serve as an effective detail. Single-component urethanes are commonly used for these high-movement façade joints, though silicone-based products are occasionally used for nonporous joint surfaces.²

• ASTM E283 – Standard Test Method for Determining Rate of Air Leakage Through Exterior Windows, Curtain Walls, and Doors Under Specified Pressure Differences Across the Specimen. Contrasting with the battery of tests to prove the air permeance rate and effectiveness of air barrier products – such as ASTM E 2178 for air-barrier materials and ASTM E 2357 or E 1677 for air-barrier assemblies – the standard E283 is an ideal metric for ensuring proper air infiltration rates at key openings within panelized metal cladding façades.

• ASTM E331—Standard Test Method for Water Penetration of Exterior Windows, Skylights, Doors, and Curtain Walls by Uniform Static Air Pressure Difference. This air chamber method (and its field-test cousin, ASTM E 1105) should demonstrate that the IMP or other metal cladding system incorporates fenestration meeting the same design penetration forces based on properly determined air-pressure differences acting across the building envelope.

• ASTM C1363—Standard Test Method for Thermal Performance of Building Materials and Envelope Assemblies by Means of a Hot Box Apparatus. For such calculations as the U.S. Green Building Council's LEED certifications, IMP envelopes can help contribute to higher energy efficiency potential. Independent testing to ASTM C 1363 ensures a thermal transmittance that at least meets ASHRAE/IESNA Standard 90.1 and in some cases provides a significant percentage improvement, to meet the LEED criteria for optimized performance.

With these key achievements in hand, the architect and project team are well-positioned to create an efficient, ecologically sound building using metal panels. There are many other codes and standards worth mentioning for such attributes as life safety—for example, metal panel cladding is ideal for meeting ASTM E 84, which evaluates surface burning characteristics—even though green building and energy use are such strong drivers for architects today.

In fact, fire-safe construction is another benefit of metal panel envelopes. The IBC calls for fire-rated wall assemblies, and for multi-story construction, the claddings must meet the National Fire Protection Association (NFPA) standard 285, which is a test for any exterior, non-load bearing wall assemblies and panels used as components of curtain wall assemblies that incorporate combustible materials, including foam plastic core insulation. The recent MCA white paper, Insulated Metal Panels and NFPA 285, notes that IMP manufacturers were among the leading proponents of this test. It requires the testing of a full two-story assembly with a window. This is costly, but MCA notes that “if the 'basic' IMP panel system meets NFPA 285, minor variations in items such as caulks, trim, window details, and joints can be allowed without retesting or an analysis.”

Renovation and Overcladding

Some of the latest changes to building codes address the need to renovate and improve the energy performance of existing buildings. For example, cities like New York have adopted new rules that allow building developers and owners to add up to 8 inches of wall thickness to new or existing façades for adding insulation without facing penalties for exceeding floor area limits. The new codes promote “not only the new green buildings, but also retrofits of existing buildings,” according to Urban Green Council. In New York, if the new buildings exceed the local energy code, the exterior wall thickness can be deducted from floor area calculations.

In this way, metal panels can be added to an existing building as a retrofit strategy to add R-value and other performance benefits—not to mention a sleek new exterior image. While a metal panel retrofit may carry a higher initial cost than some alternatives, they add benefits in terms of total life-cycle cost that can make it a long-term money saver for the owner.

“Regardless of whether the substructure is steel, wood or concrete, metal wall-panel retrofit systems can address construction that has leaks, high maintenance costs, or low energy efficiencies,” says Buchinger. “Retrofit wall applications can also help to increase the energy efficiency of a building and improve aesthetics.”