Editor's note: the following is an excerpt from the recently-published National Roofing Contractors Association's (NRCA) Architectural Sheet Metal and Metal Roofing Manual.

The following are methods for joining metal components:

  • Overlap standing seam. A minimum 7/8 in. (22 mm) high female leg should be installed over the adjoining metal shape's metal leg and crimped to complete the seam. Sometimes sealant is installed in the female leg prior to installation of the metal shape to provide additional weatherproofing capabilities. For example, the seam is secured by the button-punch method or with rivets.

  • Double lock standing seam. A minimum 7/8 in. (22 mm) high female leg should be installed over the adjoining metal shape's metal leg. The legs are folded over themselves twice to complete the double lock seam. Double lock standing seams are generally weatherproof without the addition of sealants or sealant tapes.

  • Drive cleat seam. A minimum 2 in. (50 mm) wide folded drive cleat should be installed over the folded ends of two metal shapes. The space between the ends of the metal shapes will vary depending on type of material used, gauge thickness and building locale.

  • Exposed cover plate seam. A minimum 6 in. (150 mm) wide exposed joint cover plate should be installed, evenly divided and placed, over the two edges of adjacent metal pieces. It should be attached separately allowing the metal pieces to act independently during thermal movement. The space between the ends of the adjacent metal pieces will vary depending on type of material used, gauge thickness and building locale. Each side of the space requires sealant; a minimum of two beads of sealant should be installed under the cover plate.

  • Concealed backer plate seam. A minimum 6 in. (150 mm) wide concealed joint plate should be installed, evenly divided and placed, under the two edges of adjacent metal pieces. It should be attached separately allowing the metal to act independently during thermal movement. The space between the ends of the adjacent metal pieces will vary depending on type of material used, gauge thickness and building locale. Each side of the space requires sealant; a minimum of two beads of sealant should be installed under the cover plate.

  • Cover plate with backer plate seam. A minimum 6 in. (150 mm) wide concealed joint plate should be installed, evenly divided and placed, between the two edges of adjacent metal pieces. It should be attached separately allowing the metal pieces to act independently during thermal movement. The space between the ends of the adjacent metal pieces will vary depending on type of material used, gauge thickness and building locale. Each side of the space requires sealant; a minimum of two beads of sealant should be installed under the cover plate.

  • "S" cleat seam. A minimum 2 in. (50 mm) wide "S" cleat should be installed between the unhemmed ends of two metal shapes. Sealant is recommended to be installed in the female legs prior to installation of the metal shape to provide additional weatherproofing capabilities. The space between the ends of the metal shapes will vary depending on type of material used, gauge thickness and building locale.

  • Lap seam. Simple joinery consists of overlapping the adjacent ends of two pieces of sheet metal. Sometimes mechanical fasteners or rivets are used to secure the metal in place. Succeeding pieces of metal, lapped a minimum of 3 in. (75 mm) over the preceding pieces, should be installed. A notch can be cut into the return hem along the bottom edge of the metal that receives and locks in place the preceding piece. For weatherproof installations, sealant is required in the seam.

Crimping and locking is a typical method used to join laps in sheet metal components. For example, a standing seam is a locking type of seam. Also, for example, at the outer face of a through-wall scupper where the scupper overlaps the flange, the two pieces of metal are crimped and locked together. Copings and cleats are joined in the same fashion. The gauge of metal must be considered when designing the joinery detail.

(The above manual is available from NRCA at 10255 West Higgins Road, Suite 600, Rosemont, Ill. 60018-5607; 847-299-9070; fax 847-299-1183; www.nrca.net; e-mail: nrca@nrca.net.)

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