Visual Acceptance Parameters Beyond The Codes

While the International Building and Fire Codes define a number of exterior cladding performance requirements—including material performance, structural integrity, and allowable deflection limits—a number of flatness and localized issues, such as denting and colorfastness, are not specifically addressed within the code.

To highlight the industry standards for perceived “defects” in MCM panel installations, and essentially promote a higher standard for these systems, MCA developed a useful white paper titled, Visual Acceptance Parameters for Metal Composite Material Panels and Panel Systems.

The document identifies four main areas: panel deflection, panel bow, surface imperfections, and finish performance and color fastness. Panel Deflection: Metal panel deflection is generally caused by two factors: wind load and thermal movement of the panel due to temperature change. Any expansion and contraction commonly resulting in panel deflection can easily be addressed with proper design, fabrication, and installation techniques.

Of note, MCM cladding is allowed by code to have a panel deflection of L/60, which recognizes the ability of metal cladding to deflect a considerable amount and still return to its original position without yielding the material. {{Question7}}

Panel Bow: When subjected to a change in ambient temperature, a restraint in an MCM panel can cause panel bow. The movement causes the panel to grow as the temperature rises and shrink as the temperature declines. These dimensional changes are directly related to these temperature changes in the panels when compared to the installation temperature. For example, with aluminum panels, this change in temperature can easily vary +/- 100°F from the installation temperature and cause a change in panel length of 1/8-in (per 8 feet in length) or more. If this is not considered in the panel system design, fabrication, and installation, this level of panel movement may cause visual panel bowing.

Further, movement within the structure itself, or the sub-framing may directly impact the panel flatness. Consequently, the load deflection criteria of the panel system and connection methods should be coordinated with the load deflection criteria of the primary support system to control movement and reduce significant panel bowing. To address these issues prior to installation, panel fabrication often includes slotted holes in panel framing members or use of adhesives that allow some panel movement.

Panels are usually installed with a fixed point in the center of the panel, allowing for expansion and contraction of the panel in both directions from the fixed point. While this technique can become particularly difficult around openings and at building corners, proper planning can minimize this difficulty.

Finally, consideration must be given to allow free panel movement. This means that fasteners generally should not be torqued tight against connecting extrusions, effectively locking the panels in place.

In sum, as objectionable as panel bow can be on a project, the effect is generally temporary and will often subside as the panel approaches the installation temperature.

Surface Imperfections: Not specifically addressed within the code, Imperfections typically include surface dents, dimples, abnormal core defects, and defects within the metal facing material.

As defined by the Insulated Glass Manufacturers Association’s insulating glass units and American Architectural Manufacturers Association (AAMA) 2605 Section 5.2, the Voluntary Specification, Performance Requirements and Test Procedures for Superior Performing Organic Coatings on Aluminum Extrusions and Panels, a visual inspection is made when standing 10 feet from the surface at a 90° angle, typically under natural exterior lighting conditions.

If imperfections are identified, they should be indicated to the installer for investigation and possible remediation or replacement.

Finish Performance and Color Fastness: Also not specifically addressed in the building codes, finish criteria are often defined in detail in the project specifications. These performance characteristics include, but not limited to hardness, impact resistance, wear resistance, humidity, and corrosion resistance, as defined by various ASTM, AAMA and NCCA standards.

Color fastness is measured under laboratory conditions and compares a sample of the project panel to a production control sample using one of several standard test methods.

A cleaning and maintenance standard should be included to sustain the finish of the MCM panel systems. Also of note, the performance characteristic of the detergent resistance used for cleaning should conform to the chemical resistance criteria specified in AAMA 2605.

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Working With Certified MCM Fabricators

When designing MCM exteriors, architects can significantly boost the quality of the installed panels by working with certified MCM fabricators.

Photos courtesy of 3A Composites USA

Miles Associates chose MCM for the interior design of the 65,000-square-foot atrium of the Children’s Hospital at Oklahoma University Medical Center in Oklahoma City.

Developed by MCA’s Metal Composite Material Council, certification is based on experience, the extent of services offered—i.e., project design, fabrication, installation, in-house engineering—meeting industry performance requirements, and demonstrating the company’s level of financial strength, thereby offering assurance that the company can support large projects.

For example, fabricators earn qualification points by meeting standard performance testing such as:

• ASTM E 283 Static Air Infiltration standard of no more than 0.06 cubic ft. per minute per sq. ft. at 6.24 pounds per sq. ft. (PSF) of loading
• ASTM E 330 Structural Design Load where deflection of framing members doesn’t exceed L/60 of the clear span or anchor deflection doesn’t exceed 1/16 inch at +/– 30 PSF.3
• ASTM E 331 Static Water Infiltration with no uncontrolled water passing from the panel system onto the substrate at 12.0 PSF loading
• AAMA 508 or 509 for rainscreen installation systems

In terms of quality of the services that certified MCM fabricators offer to architects, these premium subcontractors create project and shop drawings and often provide engineering calculations to verify the adequacy of the panel system design. The fabricator also takes responsibility for designing, sourcing, and fabricating all structural components including extruded aluminum, fasteners, and clips.

Quality control procedures used by certified subcontractors can identify problems early, before installation, avoiding time-consuming delays and modifications. In addition, by selecting selected certified MCM fabricators, architects are ensuring that the fabricated systems will meet performance requirements in the area of water penetration, structural performance, and visual appearance.

In Conclusion

While MCMs are more commonly used in a variety of commercial applications for today’s buildings, many architects may not be aware of the extent of their capabilities in the realm of design. From unique shapes and curves to textures and patterns to bold and trendy colors, MCMs are an amazing tool in an architect’s design toolbox.

Sustainable and cost effective, this long-lasting, exceptional fire protection material is a great option for projects seeking both sleek, stand-out designs and more traditional facades. As more retail, healthcare, office, automotive, convention centers, and multi-family buildings select MCM wall cladding, their popularity is expected to continue growing.