Nonvented ridge caps
Steep-slope metal roof systems, also called architectural metal panel roof systems, are one of the fastest-growing segments of the roofing industry. These systems are used in commercial and residential applications and require installation over a solid substrate, such as plywood, and use of an underlayment. Although underlayment is used as a secondary protection against moisture infiltration, proper flashing details are necessary to prevent moisture from initially bypassing a steep-slope metal panel roof system.
The NRCA Roofing and Waterproofing Manual, Fifth Edition, which provides 26 details for architectural metal panel roof systems, includes detail A-MTL-4, "Non-venting ridge cap flashing." The detail provides the most common and effective method for flashing a ridge. A ridge cap is used to complete the weatherproofing system where panels meet at a ridge.
Detail A-MTL-4 provides multiple lines of defense against moisture infiltration. The first line is the "Z" closure, which is set in continuous sealant (either a bead or tape); this includes sealing the vertical legs of the "Z" closure to the panel seams. Mechanical fasteners generally are used to secure the closure to the panel; depending on the metal type, soldering the "Z" closure to the panel also is acceptable.
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