Suggestions on the installation

of flat-seam metal roofs

(The following is taken from the recently published sixth edition of SMACNA's Architectural Sheet Metal Manual.)

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 dorms. The seams may be sealed, except where the pitch is less than 3 inches per square 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 edges on both sides of the sheet.

Pans are formed by notching and folding the sheets as shown in Detail No. 1. The pans are held in place by cleating, as shown. After pans are in place, all seams are malleted and soldered or sealed.


Copper, minimum 16 ounce, 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 across the top and tapered equally to 2 1/4 inches at the bottom.

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 No. 2 shows the junction of a roof and parapet wall. Metal base flashing is cleated to deck on 24-inch centers and extended up the wall 8 inches. Pans are locked and soldered to base flashing. Metal counter flashing covers 4 inches of the base flashing.

Detail No. 3 illustrates 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.

(For information on ordering the Sheet Metal and Air Conditioning Contractors' National Association's Architectural Sheet Metal Manual, Sixth Edition, write SMACNA, 4201 Lafayette Center Drive, Chantilly, VA 20151-1209; call (703) 803-2989; see on the Internet.)