Copper Sheet and Copper Applications Preparation: Sheet and copper applications in construction are inevitably required to provide some level of resistance to water penetration. Anything that can cause punctures or openings in the copper membrane should be avoided. Copper roofs, valley flashings, and gutter linings should always be applied on a smooth, dry, stable surface with no projecting nail heads or other imperfections. Properly designed expansion joints should accommodate movement in the substrate.
In such applications, an approved underlayment, usually saturated felt, must be applied to the substrate. The felt acts as a cushion for the copper sheets. A sheet of rosin-sized building paper should be inserted between the copper and the underlayment. This will prevent bonding between the two surfaces that would otherwise restrict the thermal movement of the copper. The only exceptions to this requirement are applications where the copper is not intended to move, not even under thermal stress. For example, continuous cleats and edge strips are nailed down, usually in a staggered pattern of nails 3 inches on center, to limit movement. Flat seam copper roofing, also, does not require a slip-sheet, since it is not designed to allow movement.