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.
Detail A-MTL-4 from The NRCA Roofing and Waterproofing Manual, Fifth Edition
In addition, the "Z" closure also provides the base securement for the one-piece metal ridge cap. The ridge cap is attached to the "Z" closure simply by hemming the ridge cap on both sides. Fasteners may be used to provide additional attachment.
The second line of defense is the upturned panel end. The detail provides this as an option, but conservative roofing practice incorporates this additional protection against moisture infiltration.
The last line of defense is the required underlayment, which is installed over the ridge line of the roof deck. The underlayment on each side of the ridge should extend under the panel on the opposite side.
A properly installed ridge cap detail should provide weatherproofing for the service life of a metal roof system.
James R. Kirby is an NRCA senior director of technical services.
COMMENTS
Be the first to comment. Please log in to leave a comment.