This section is from the book "A Treatise On Architecture And Building Construction Vol3: Stair Building, Ornamental Ironwork, Roofing, Sheet-Metal Work, Electric-Light Wiring And Bellwork", by The Colliery Engineer Co.. Also available from Amazon: A Treatise On Architecture And Building Construction.
These flashings, and those around all other forms of movable finials, require much attention to detail, as they must be made water-tight, and remain water-tight under peculiar conditions. Every flagpole sways more or less, according to its strength, the pressure of the wind, etc., and,therefore, a rigid flashing at its base cannot be durable. The liability of the pole to "settle down" is another item to be considered. On this account it is advisable to use slip joints or telescope flashings, which are provided with enough clear space or "play" to allow the pole to move or sway in any direction without touching or affecting the sheet-metal covering of the dome. A good arrangement is shown in Fig. 54, which is, in fact, a detail of the intersection between the flagpole and the cupola shown in Fig. 51. The rolls of the dome finish inside of the bead a. The copper work finishes around the top member b. An 8-pound per square foot sheet-lead bonnet c encircles the pole and covers the member b. The top of the bonnet is "dressed " close into a small groove in the pole, which is cut just deep enough to allow the lead to finish flush, a bed of red and white lead being used to make the connection water-tight. The bonnet is nailed to the pole with a ring of 1-inch, pointed, flat-head copper nails, which may be concealed with a bead d if desired. The lower edge of the bonnet overhangs the block b and forms an open lap joint around the top of the copper. The top of the block b is well greased, and the bonnet is free to slide as the pole sways. When the pole intersects a flat roof, a plain slip-joint connection, like that shown in Fig. 55, may be used. A cylinder, or upstand, a is soldered to the roof. A sleeve b overhangs the upstand and is nailed to the pole as shown,a space being provided on each side of the upstand to allow the pole and its flashings to move in any direction.