Additional factors that demand close attention when specifying single-skin metal panels, MCMs, or IMPs:
✔ Possible galvanic corrosion. Be careful that you are not putting aluminum and steel together. You don’t want to substitute components without knowing whether dissimilar metals are touching, which could promote corrosion.
✔ Potential chemical interactions between metal and other materials. “In Colorado, we are seeing zinc being used in conjunction with cedar shakes,” says Linda McGowan, PE, AIA, president of Building Consultants & Engineers, Littleton, Colo. “The tannic acids in the cedar tend to degrade the zinc.” This problem can sometimes be addressed through the use of paint finishes, says Paul R. Bertram, Jr., FCSI, CDT, LEED AP, Kingspan’s director of environment and sustainability.
✔ Fire code compliance. Some fire codes prohibit cladding composite material containing polyethylene, used in some metal panel cores, above a certain height. Another core material, often mineral-based, must be used above the height limitation.
✔ Hurricane-zone code compliance. Many metal panel systems are rated for hurricane zones, but this must be demonstrated by such tests as Miami-Dade TAS 201-94 (impact), 202-94 (uniform static air pressure), and 203-94 (cyclic wind pressure loading) or ASTM E1886-05 and E1996-09, says CSI president-elect Bertram. Mark Baker, PE, president of IBA Consultants, Coral Springs, Fla., adds, “On a couple of projects, we have had to put a hurricane-resistant wall behind metal panels to comply with code.” In the U.S., this is of particular concern in the hurricane-zone areas within a mile of the water on the East Coast and Gulf Coast.
✔ Choose the right gauge thickness. Heavier gauge metals are generally more expensive, but hold their shape better. Oil canning (perceived waviness in the metal skin) can result from using an inappropriately thin material.
✔ Beware sealant degradation. Because metal is such a robust heat conductor, direct sun can raise temperatures high enough to degrade certain sealants. Butyl sealants resist heat better than silicone. Exposure to UV light can also degrade some sealants.