The sheets having been fastened at the sides by means of the rolls as above described, it next becomes necessary to make a connection between the lower edge of each sheet and the upper edge of the sheet next below it on the slope of the roof (Fig. 117).
This is done by means of the joint shown in section in Fig. 119 and called a Welt or Fold joint.
In this figure the hatched section is that of a "clip," or strip of zinc about 2 inches wide nailed to the boarding, and doubled in between the edges of the two sheets to be connected, which are shown in section by the black lines, so as to make a secure joint, and yet to give them plenty of play for expansion and contraction.
"Welted joints are used only when the roof has a slope of 1/7 or more; for flatter roofs drips are introduced.
The lower edges of the sheets nearest the eaves are strengthened where they project over the gutter, by being doubled back so as to form a bead; and further, by a strip of stout zinc (S in Fig. 117), nailed along the edge of the boarding over which the bead is formed.
The ridge is covered by a zinc roll cap turned over it, which latter is strengthened on the lower edges by their being bent round to form beads.
Zinc may be fixed with rolls on boarding laid upon roofs of any pitch not less than about 1 in 15.
When, however, the slope of the roof is flatter than 1/7, drips should be formed similar to that shown in Figs. 120, 121, at intervals of from 7 to 8 feet, that is at the end of each sheet.
Fig. 120. End Sectional Elevation.
Fig. 121. Side Sectional Elevation.
The figures show the end elevation and the section of a drip joint over a roll.
The thick lines show the sections of the sheets, the ends of which, it will be noticed, are bent inwards, so that they may be able to expand and contract without danger of any water getting in behind the joint.
The stopped end of the roll cap on the upper level is bent over with the edge of the sheet.
Drips in flats should be 2½ inches deep, and in gutters 1½ inch deep.
Another form of roll patented by the Vielle Montagne Zinc Company is recommended as lasting longer than the simple form just described, and as being peculiarly suitable " for terraces or flats of warehouses where weights are stored, or where there is much walking about;" and, as regards appearance, for Mansard or high-pitched roofs.
The method of laying zinc with these rolls is somewhat similar to that with the ordinary rolls; but the loose zinc roll cap is done away with, the zinc being drawn tight over the roll by machinery.