•The common size of tin shingles for flashing is 5x7 inches, the shingles being laid lengthways. on the roof and turned up 2 ½ inches. This is the smallest size that should be used, and in ex-posed places or on rather Flat roofs they should be larger, say 7x7 inches, or 7x9 ½ Inches, so chimneys, or where the roof abuts against any brick or stone wall is done in the same manner as against wooden walls, except that the flashings should be not less than 7 inches wide, and they should be covered by "counter flashings"
These counter flashings consist of pieces of metal, preferably 3 or 4-pound sheet lead, wedged or built into the joints of the mason work and turned down over the flashings. They should be placed at least 6 inches above the roof, and in places where snow is likely to lodge correspondingly higher. It is much better to build the counter flashings into the joints of the mason work as the latter is laid, as the flashings are more securely held and a tighter joint can be made. When not built in, the joint should be raked out and the counter flashings inserted and wedged with metal, and the joint tightly pointed with elastic cement. The bottom of the counter flashing should be not more than 1 inch above the roof.
Behind the chimney a "cricket" or A should be built and cov-ered with metal to prevent snow and water from lodging there. Fig. 177 shows a portion of a chimney flashed in the method above described, which is the same for either shingles or slates.
Back of towers, or any place where snow is liable to collect, the flashing should be carried high enough both on the roof and wall that the water from the melting snow will not rise above it, and the joints should be locked and soldered like an open valley.
Where a shingle roof comes against a stone or brick gable wall, finished with a stone or terra cotta coping, the bottom of the coping should be kept at least 4 inches above the shingles, and the flashing should extend to within ½ inch of the coping. The counter flashing should be laid in the joint before the coping is set, and the coping should project over it.
Where there is a large stone, as a kneeler, or finial, a groove should be cut in the back of the stone, on a line with the bottom of the coping, and the counter flashing wedged into the groove and pointed with elastic cement. Such places on large roofs are frequently a source of trouble, and the flashing and counter flashing should be done with the greatest care.
The curbs of skylights and all parts rising from or coming against the roof should be carefully flashed. If the young architect wishes to establish a reputation for tight roofs he must be very particular to specify suitable flashing and counter flashing, and of ample width, as the builder will not be likely to put in more than is required.