To avoid leakage on domes by the effects of expansion and contraction, and to prevent any solder from discoloring the copper work, some form of ribbed covering is employed. This requires the use of a standing or a roll seam, as the character of the building may demand.

The space between the standing seams or rolls should not be more than 2 feet wide, and the sheets should not be more than 4 feet long. They must be securely supported from the top edge, preferably with heavy cold-rolled copper cleats.

It is advisable in all first-class sheet-metal roofing to avoid driving nails through the sheets at any point. The sheets are thus permitted to freely expand and contract without tearing the metal.

An excellent roll seam is shown in Fig. 48. The batten, or roll strip a is nailed down over a long cleat strip b. The sheets c, c are then sprung in between the rolls, and the cleat strip is doubled over the upstand. The roll cap d is then put on over the roll, and locked into the cleated upstand as shown. The roofing sheets, cleat strips, and roll caps are thus all locked together and made water-tight, and yet are free to expand and contract individually. The batten nails combined with the outward curvature, which the sheets c must necessarily have, will prevent a gale from rattling or loosening the sheets.

65 Ribbed Surface Covering 426

Fig. 48.