Kinds Of Leaders

Rain leaders may be divided into inside leaders and outside leaders. Inside leaders are located within some parts of the building secure from frost, and are installed by the plumber. They are made of cast iron or wrought iron pipe and put together perfectly gas and water-tight. Outside leaders are usually made of sheet metal with loose slip joints, and from a point about 5 feet above grade, are installed by the sheet metal worker. Up to a point 5 feet above grade outside leaders should be of cast iron or wrought iron pipe to withstand the rough usage they are likely to receive.

Trapping Of Leaders

Rain leaders usually are trapped with a running trap placed in the horizontal part of the leader just inside the cellar wall, secure from frost. When inside leaders are used, however, or when outside leaders are made perfectly gas and water-tight and do not open near windows, doors, flues or ventilator shafts, a better practice is to omit the trap and use the leader also for a vent pipe.

Fig. 16

Roof Connections

Inside rain leaders should be connected to the roof gutter by means of a short length of 8-pound lead, or 18-ounce seamless drawn copper tubing, securely soldered to the gutter and calked or screwed into the iron pipe by means of solder nipples or brass ferrules solder wiped to the lead or copper pipe. The mouth of the leader should be made funnel-shaped to provide an easy entrance for the rain water without loss of head, and the inlet should be protected with a brass wire basket to keep out leaves and other foreign matter. Roofs that are surrounded with parapet walls should have overflows built in them through which water can escape in case the leader inlet is obstructed with ice.

Outside leaders should be provided on the top with a service box, into which the roof water can discharge. This service box should be set low enough so that in case the leader becomes stopped with ice, the water can overflow the box without backing up on the roof. The principal objection to outside leaders is that they freeze and burst. In cold climates outside leaders are a source of worry and expense that can be avoided by the additional first cost of inside leaders. The bursting of outside leaders from frost can be reduced to the minimum by using corrugated pipe in place of cylindrical; then, when the water expands upon freezing, the corrugations yield to the pressure without the pipes bursting. Cast iron pipe with lead calked joints never should be used for soil waste or leader pipes where exposed to frost. Even though the pipe is usually empty, the oakum used in calking the joints becomes wet from the water flowing through the pipe, which, upon freezing, forces the lead out of the joints, causing leaks.

Size Of Leaders

Rain leaders never should be less than 2 inches in diameter. For leaders larger than 2 inches in diameter the size can be determined by the rule for determining the size of house drains. In applying this rule, however, the fall of the horizontal portion of the leader must be taken for the head, as the leader, when running full with only the head due to the grade, must be of sufficient size to carry off the greatest possible rainfall. The following simple empirical rule, which is derived from the foregoing rule, will determine the size of leaders with sufficient accuracy for all purposes :

Rule

Allow 1 square inch in sectional area of the leader for each 250 square feet of projected roof surface.

Example

What size of leader will be required to drain a roof 75 feet long by 50 feet wide?

75x50 Solution

= 15 square inches, and from Table VI it is found that a 4 1/2-inch pipe has an area slightly greater than 15 inches.

The area in square inches and in square feet of pipes from 2 inches to 12 inches in diameter can be found in table VI:

Table VI - Diameter And Area Of Pipes

Yard and area drains

Yard and area drains in a sense are rain leaders. Their object is to remove storm water from yard and area surfaces; therefore, what has been written about the size and materials of rain leaders will apply equally to yard and area drains.

Yard and Area Catch Basins (Fig. 17) are simply plain cast iron receptacles with removable perforated covers; they are located in the yard or area to be drained for the rain water to drain into. Catch basins should be so constructed that all water will drain out of them immediately, and the area of perforations in the covers should be equal to twice the area of the drain pipe.

Fig. 17

Trapping Yard And Area Drains

Yard and area drains should be trapped with running traps located inside of the foundation walls where they are accessible and safe from frost. When convenient to do so they should connect to a rain leader. If the rain leader is trapped the yard or area drain should connect to it on the yard side of the trap, and the leader trap will then serve for both. The objects of connecting a yard or area drain to a rain leader are to insure a permanent seal to the trap, or in the event of the seal failing, to provide a draft, down through area drain and up through the rain leader.