The following is taken from the Sheet Metal and Air Conditioning Contractors’ National Association’s Architectural Sheet Metal Manual.

Figure 6-2 illustrates some of the many sections of metal-roof deck available from manufacturers. Decks are made for short-, intermediate- and long-span construction and are applicable to most any type building. Decking is available in painted steel, galvanized steel and aluminum.

Figure 6-2A, B, and C are light-gauge decking used with narrow-span construction. Figure 6-2D and 6-2E are for intermediate-span construction.

Figure 6-2F and G are long-span decks. Integral plates are provided with figures 6-2E and G, which can serve as a ceiling, or the deck may be inverted to use as a smooth surface for the roof.

Roof deck is normally installed by welding or by mechanical fasteners. The manufacturer’s recommendations for installation of the deck selected should be followed.

Flat-seam roofs

Figure 6-3

The flat-seam method of roofing, as illustrated in Figure 6-3, is most commonly used on roofs with a slight pitch. However, the flat-seam method is also used for covering towers or domes. The seams may also be sealed except where the pitch is less than 3 inches per foot, in which case they must be soldered.

Expansion battens would be used at building-expansion joints.

Before the roof is installed, the wood deck should be thoroughly dry, smooth and covered with 30 pounds of felt and building paper. Roofing-support systems for flat-seam roofs should have continuous (solid) sheathing for metal support.

It is recommended that flat-seam roofing be from pans made from sheets 20 by 28 inches. For soldered joints, these pans may be pre-tinned 1 1/2 inches back from all the edges on both sides of the sheet.

Pans are formed by notching and folding the sheets as shown in Detail 1. The pans are held in place by cleating, as shown. After pans are in place, all seams are malleted and soldered or seamed.

Copper, minimum 16-ounce or 0.0015 dead-soft stainless steel is recommended for flat-seam roofs.

Flat-seam roofs that exceed 30 feet in any direction should not be divided into sections with a maximum width of 30 feet to accommodate expansion. Sections should be separated by 1 5/8-inch-tall wooden expansion battens that are 3 inches wide across the top and tapered equally to 2 1/4 inches at the bottom — see Batten Detail 1 in Figure 6-7 (not shown) for a similarly tapered but differently dimensioned batten. The expansion batten is covered with 8- to 10-foot lengths of metal locked and soldered together with 4-inch horizontal flanges and right-angle bends in one piece. The flanges extend onto the roof deck and are locked and soldered to the roofing pans.

Detail 2 shows the junction of a roof and parapet wall. Metal base flashing is cleated to deck on 24-inch centers and extended up-wall 8 inches. Pans are locked and soldered to base flashing. Metal counter flashing covers 4 inches of the base flashing.

Detail 3 illustrates the installation of flashing at the edge of the roof. Flashing is formed as shown and attached to the face by a continuous cleat nailed on 12-inch centers and is cleated to the roof deck. Pans are locked and soldered or sealed to the flashing.

To order copies of SMACNA’s Architectural Sheet Metal Manual, write 4201 Lafayette Center Drive, Chantilly, VA 20151-1209; see www.smacna.org on the Internet.