either side of a partition (as shown in the illustration).
A point to note is that the waste from both fixtures
discharges into a double sanitary tee.
A CIRCUIT VENT serves a group of fixtures. As
shown in figure 3-37, a circuit vent extends from the
main vent to a position on the horizontal branch
between the last two fixture connections. Make sure
that a maximum of eight fixtures are put on any one
circuit. If you have more than eight fixtures to be
circuit vented, use two circuits instead of one. In this
type of vent, water and waste discharged by the last
fixture tends to scour the vents of other fixtures on the
A vent pipe, in which liquid wastes flow through
a portion of it, is known as a WET VENT. A LOOP
VENT is the same, except it connects into the stack
unit to form a loop. This type of vent may be used on
a small group of bathroom fixtures, such as a
lavatory, water closet, and shower, as shown in
figure 3-38. The pipe for a wet vent installation
should be sized to take care of the lavatory, the water
closet, and the shower.
Figure 3-37.Water closets circuit vented.
Figure 3-38.Wet vent.
When you are draining more than four fixture
units, the wet vent should never be under 2
inches in diameter. A water closet must not
drain into a wet vent.
As shown in figure 3-38, the lavatory should be
individually vented. This is necessary to prevent loss
of the trap seal through indirect siphonage. Another
point to note with the lavatory is that the relatively
clean water discharged from it tends to scour the wet
vent, preventing an excessive buildup of waste
material in the vent.
A venting system must be installed properly with
little repair and upkeep. This section points out your
duties in installing vent systems.
Refer to figure 3-39. Notice that a MAIN VENT
TEE forms a junction between the main vent and the
main soil and waste vent. This is a tapped tee having a
stack side outlet. It should be installed by caulking in
the vertical stack, at least 6 inches above the overflow
level of the highest fixture connected. After this has
been done, the vertical stack should be extended, full
size or larger, through the roof to form the vent
terminal. The pipe must extend at least 6 inches above
the roof. If the roof is used for other than weather
protection, the vent terminal must be 7 feet above the
roof. The opening in the roof through which the main
soil and waste vent runs must be properly
waterproofed. Roof flashing is used for this purpose
Roof flashing is made of galvanized iron or copper.
Flashing is available in different sizes. Normally, the
size of flashing needed for a job is determined by the
size of the main soil and waste vent.
When installing roof flashing on a shingled roof,
extend it under two courses of shingles above the pipe.
On a flat roof, place it between layers of the roofing
material and have the finishing layer over the top of the
flashing. To complete the installation on either type of
roof, always apply a coat of roofing cement as added
protection against leakage.
In a cold climate, you must think about ways to
prevent closure of the main soil and waste vent at the
roof outlet by freezing. The air discharged by the main
stack and waste vent is humid and condenses. This