On the preceding plate the continuous vent is shown in a special application to two-floor work for four-flat apartment buildings. In Plate 28 the continuous vent is shown as applied to double lines of fixtures on three or more floors. Such double lines of fixtures are often to be found in double apartment buildings.
In the larger cities such buildings are often many stories in height, and in the towns and smaller cities double apartment buildings of three and four stories are very common.
In office buildings, also, fixtures are often so located that two of them on the same floor, and on opposite sides of a wall or partition, waste into the same stack. The work shown in Plate 28 applies to many cases of similar nature. The waste from each of the two adjacent fixtures is carried into the same waste fitting, from the bottom of which a mutual waste is run to the waste stack, and from the top a mutual vent to the vent stack.
In addition to gaining for each fixture the advantages derived from continuous venting, the work may often, and in fact usually, be done with less labor and material than if installed with the customary crown venting. While the matter of saving in the cost of construction might be questionable in the case of a single line of fixtures, the addition of a second line of fixtures requires no additional material or labor, with the exception of the furnishing of the traps and connecting them to the waste fittings.
The system shown is an excellent one, and without doubt will gradually come into general use, a result much to be desired. The entire system shown is of cast iron, but it may be said that for the main vent, and especially for the fixture wastes and vents, wrought iron is more generally used. In the case of the mutual fixture wastes and vents, wrought iron will effect a saving in expense, as sizes smaller than 2 in. may often be used, and cast-iron pipe is not made in sizes smaller than 2 in.
The fixture vent should pitch upward from the trap at all points in order that condensation may drain into the trap, and it should be connected into the main vent line at a point higher than its fixture, so that, in the event of stoppage of the trap or waste, the fixture waste may not pass off through the vent.
To provide against the latter evil, it is good practice in the case of a group of fixtures whose vents connect into a main branch vent, to run this branch so that its lowest vent fitting shall be at least two or three inches above the top of the highest fixture of the group.
Plate XXVIII. Continuous Venting For Two Lines Of Fixtures On Three Or More Floors - Practical Requirements Of Venting
Continuous Venting for Two Lines of Fixtures
Formerly much vent work of lead was used, but the best practice to-day calls for the use of galvanized iron or brass on all branch, main branch, and individual fixture vents of 2 in. or less in size. The use of lead for vent work is fast becoming limited to use in connection with lead traps, short connections being made into the wrought-iron or brass pipe.
Main branch vents should be increased one size in diameter after passing 30 ft.
When a fixture is located 8 ft. or more from the main vent, its trap vent should either be carried independently through the roof, or enter the main vent stack above all fixtures.
Thus, in the case of the lavatory of Fig. C, Plate 20, if its distance is 8 ft. or more from the stack, its vent should be run as above; if its distance is 6 ft. or more, lead should not be used on its waste. Under such conditions the use of the continuous vent for the fixture, as shown, is excellent practice.
Under Plate 13, it was shown that the main vent line might either run independently through the roof or reenter the soil or waste vent above the highest fixture. In many of the large cities this demand is qualified by requiring the running of a main vent separately through the roof, whenever such vent serves fixtures on more than six floors or extends more than 80 ft. above the grade line.
Whenever main vent lines are reentered into soil or waste vents, no fixture should be located on any floor above such reentrance, and be connected to the soil, waste, vent, or back-vent pipes from fixtures on floors below.