A parapet gutter for a building of modern fireproof construction is shown in Fig. 37. The only notable difference between this and the other box gutters, already described, is the fact that the gutter is located behind a wall which is higher than the point to which the gutter is extended under the slates. It will be readily seen that there is great danger of the building being flooded if the leader opening should become covered with leaves or dirt, so that the rain water cannot escape down the conductor pipe a as fast as it flows into the gutter. To avoid this difficulty an overflow tube b having a sectional area at least equal to, but preferably greater than, that of the conductor pipe, should extend through the wall as shown.

The bottom of the overflow opening should not be less than 5 inches above the lowest point of the gutter bed, but not high enough to cause the water to overflow any upstands or flashings that the gutter may be provided with. In the figure, the sheet copper composing the gutter and the rear covering of the parapet wall is all in one piece, consequently, the main consideration in locating the overflow tube here is to prevent the water from backing up under the slates and leaking over the top edge of the flashing. The sill of this gutter, like that shown in Fig. 35, is filled in with cement and graded down to the conductor opening.

48 Parapet Gutters 414

Fig. 36.

48 Parapet Gutters 415

Fig. 37.

When the parapet wall is extended higher than about 18 inches or 2 feet above the gutter, it is customary to flash the back into the wall, as shown at a, in Fig. 38. A joint in the brickwork is raked out to a distance of about 1 1/2 inches,, and the copper is bent over and let in as shown. Soft cast-lead bats b, b are then driven solidly into the raglet, about 6 or 8 inches apart, and the raglet is then filled with elastic cement. The objection to this arrangement, however, is that the expansion and contraction of the gutter is likely to loosen the bats, and the raglet joint may leak.

48 Parapet Gutters 416

Fig. 38.

49. A better arrangement is shown in Fig. 39, in which the gutter is not nailed down or secured at any point except at the conductor opening. The upstand a back of the parapet is held down by a number of cleats b, of which the tops are doubled over the top of the upstand and the lower ends are bedded in the cement sill. A counterflashing c of lead or copper is batted into the raglet and overlaps the upstand at least 3 inches. The top of the overflow tube d should be on a line with the top of the upstand or a little below it. To avoid nailing down the gutter at the back, also to prevent it from rising or shifting, an iron or brass tilting fillet e is bolted to the fireproof roofing. The sheet copper is bent under and doubled over this fillet, as shown. The tilting fillet is also advantageous to the slater, because it enables him to start his bottom course with the proper cant.