Waste Plumbing
downhill, and normal atmospheric pressure must be
maintained throughout the system at all times. Cleanouts
are located to facilitate removal of solid wastes
from clogged pipes.
and large buildings. Cast iron was invented in Germany
in 1562 and was first used in the United States in 1813.
It is durable and corrosion resistant. Cast iron is hard
to cut, and was formerly joined at its hub joints using
molten lead. Today, cast-iron pipes use hubless or belland-
spigot joints and fittings or a neoprene (flexible
plastic) sleeve.
Plastic pipes made of ABS or PVC plastic are lightweight
and can be assembled in advance. Copper pipes
have been used since ancient times. Some building
codes also allow galvanized wrought iron or steel pipes.
Engineers size waste plumbing lines according to
their location in the system and the total number and
types of fixtures they serve. Waste piping is laid out as
direct and straight as possible to prevent deposit of
solids and clogging. Bends are minimized in number
and angled gently, without right angles. Horizontal
drains should have a 1 : 100 slope (_ in. per foot) for
pipes up to 76 mm (3 in.) in diameter, and a 1:50 slope
in. per foot) for pipes larger than 76 mm. These large,
sloping drainpipes can gradually drop from a floor
through the ceiling below and become a problem for
the interior designer.
Cleanouts are distributed throughout the sanitary
system between fixtures and the outside sewer connection.
They are located a maximum of 15 meters (50 ft)
apart in branch lines and building drains up to 10 cm
(4 in.). On larger lines, they are located a maximum of
30.5 meters (100 ft) apart. Cleanouts are also required
at the base of each stack, at every change of direction
greater than 45 degrees, and at the point where the
building drain leaves the building. Wherever a cleanout
is located, there must be access for maintenance and
room to work, which may create problems for the unwary
interior designer.
Fixture drains extend from the trap of a plumbing
fixture to the junction with the waste or soil stack.
Branch drains connect one or more fixtures to soil or
waste stacks. A soil stack is the waste pipe that runs from
toilets and urinals to the building drain or building
sewer. A waste stack is a waste pipe that carries wastes
from plumbing fixtures other than toilets and urinals.
It is important to admit fresh air into the waste plumbing
system, to keep the atmospheric pressure normal
and avoid vacuums that could suck wastes back up into
fixtures. A fresh-air inlet connects to the building drain
and admits fresh air into the drainage system of the
building. The building sewer connects the building
drain to the public sewer or to a private treatment facility
such as a septic tank.
Floor drains are located in areas where floors need
to be washed down after food preparation and cooking.
They allow floors to be washed or wiped up easily in
shower areas, behind bars, and in other places where
water may spill. Interceptors, also known as traps, are intended to
block undesirable materials before they get into the
waste plumbing. Among the 25 types of interceptors are
ones designed to catch hair, grease, plaster, lubricating
oil, glass grindings, and industrial materials. Grease
traps are the most common. Grease rises to the top of
the trap, where it is caught in baffles, preventing it from
congealing in piping and slowing down the digestion
of sewage. Grease traps are often required by code in
restaurant kitchens and other locations.
Sewage ejector pumps are used where fixtures are below
the level of the sewer. Drainage from the below-grade
fixture flows by gravity into a sump pit or other receptacle
and is lifted up into the sewer by the pump. It is
best to avoid locating fixtures below sewer level where
possible, because if the power fails, the equipment shuts
down and the sanitary drains don’t work. Sewage ejector
pumps should be used only as a last resort.
Residential Waste Piping
The waste piping for a residence usually fits into a
15-cm (6-in.) partition. In smaller buildings, 10-cm
(4-in.) soil stacks and building drains are common. It
is common to arrange bathrooms and kitchens back-toback.
The piping assembly can then pick up the drainage
of fixtures on both sides of the wall. Sometimes an extra-
wide wall serves as a vertical plumbing chase, which
is a place between walls for plumbing pipes. Fitting both
the supply and waste plumbing distribution trees into
the space below the floor or between walls is difficult,
as larger waste pipes must slope continually down from
the fixture to the sewer. Some codes require that vertical
vents that penetrate the roof must be a minimum of
10 cm (4 in.) in diameter, to prevent blocking by ice in
freezing weather; such a requirement, of course, adds
another space requirement between walls.
Large Building Waste Piping Systems
In larger buildings, the need for flexibility in space use
and the desire to avoid a random partition layout means
that plumbing fixtures and pipes must be carefully
planned early in the design process. The location of the
building core, with its elevators, stairs, and shafts for
plumbing, mechanical, and electrical equipment, affects
the access of surrounding areas to daylight and views.
When offices need a single lavatory or complete toilet
room away from the central core (as for an executive
toilet), pipes must be run horizontally from the core. In
order to preserve the slope for waste piping, the farther
the toilet room is located from the core, the greater
amount of vertical space is taken up by the plumbing.
Wet columns group plumbing pipes away from
plumbing cores to serve sinks, private toilets, and other
fixtures, and provide an alternative to long horizontal
waste piping runs. Wet columns are usually located at
a structural column, which requires coordination with
the structural design early in the design process. Individual
tenants can tap into these lines without having
to connect to more remote plumbing at the core of the
building.
When running pipes vertically, a hole in the floor
for each pipe is preferred over a slot or shaft, as it interferes
less with the floor construction. Where waste
piping drops through the floor and crosses below the
floor slab to join the branch soil and waste stack, it can
be shielded from view by a hung ceiling. An alternative
method involves laying the piping above the structural
slab and casting a lightweight concrete fill over it. This
raises the floor 127 to 152 mm (5–6 in.). Raising the
floor only in the toilet room creates access problems, so
the whole floor is usually raised. This creates space for
electrical conduit and to serve as an open plenum
for heating, ventilating, and air-conditioning (HVAC)
equipment as well.
WASTE COMPONENTS OF
PLUMBING FIXTURES
Originally, the pipe that carried wastewater from a
plumbing fixture ran directly to the sewer. Foul-smelling
gases from the anaerobic (without oxygen) digestion in
the sewer could travel back up the pipe and create a
health threat indoors.
The trap (Fig. 10-2) was invented to block the waste
pipe near the fixture so that gas couldn’t pass back up
into the building. The trap is a U-shaped or S-shaped
section of drainpipe that holds wastewater. The trap
forms a seal to prevent the passage of sewer gas while
allowing wastewater or sewage to flow through it. Traps
are made of steel, cast iron, copper, plastic, or brass. On
water closets and urinals, they are an integral part of the
vitreous china fixture, with wall outlets for wall-hung
units and floor outlets for other types.
Drum traps are sometimes found on bathtubs in
older homes. A drum trap is a cylindrical trap made
from iron, brass, or lead, with a screw top or bottom.
Water from the tub enters near the bottom and exits
near the top, so the wastewater fills the trap and creates
a water plug before flowing out. Sometimes the screwoff
top, called a cleanout, is plated with chrome or brass
and left exposed in the floor so it can be opened for
cleaning. Drum traps can cause drainage problems because
debris settles and collects in the trap. If not
cleaned out regularly, these traps eventually get com-
Figure 10-2 Trap.
pletely clogged up. Drum traps should be replaced during
remodeling.
Every fixture must have a trap, and every trap must
have a vent. Each time the filled trap is emptied, the
wastewater scours the inside of the trap and washes debris
away. Some fixtures have traps as an integral part
of their design, including toilets and double kitchen
sinks. There are a few exceptions to the rule that each
fixture should have its own trap. Two laundry trays and
a kitchen sink, or three laundry trays, may share a single
trap. Three lavatories are permitted on one trap.
Traps should be within 0.61 meters (2 ft) of a fixture
and be accessible for cleaning. If the fixture isn’t
used often, the water may evaporate and break the seal
of the trap. This sometimes happens in unoccupied
buildings and with rarely used floor drains.
VENT PIPING
The invention of the trap helped to keep sewer gases out
of buildings. However, traps were not foolproof. When
water moving farther downstream in the system pushes
along water in front of it at higher pressures, negative
pressures are left behind. The higher pressures could
force sewer water through the water in some traps, and
lower pressures could siphon (suck) water from other
traps, allowing sewer gases to get through (Fig. 10-3).
Vent pipes (Fig. 10-4) are added to the waste piping
a short distance downstream from each trap to prevent
the pressures that would allow dirty water and
sewer gases to get through the traps. Vent pipes run upward,
join together, and eventually poke through the
roof. Because the roof may be several floors up and the
pipes may have to pass through other tenants’ spaces,
adding vent pipes in new locations can be difficult. The
vent pipe allows air to enter the waste pipe and break
the siphoning action. Vent pipes also release the gases
of decomposition, including methane and hydrogen
sulfide, to the atmosphere. By introducing fresh air
through the drain and sewer lines, air vents help reduce
corrosion and slime growth.
The vent pipes connect an individual plumbing fixture
to two treelike configurations of piping. The waste
piping collects sewage and leads down to the sewer. The
vent piping connects upward with the open air, allowing
gases from the waste piping to escape and keeping
the air pressure in the system even. This keeps pressure
on foul gases so that they can’t bubble through the trap
water, and gives them a local means of escape to the
outdoors.
The vent must run vertically to a point above the
spillover line on a sink before running horizontally
so that debris won’t collect in the vent if the drain
clogs. Once the vent rises above the spillover line, it
can run horizontally and then join up with other vents
to form the vent stack, eventually exiting through
the roof.
When all fixtures are on nearly the same level, a separate
vertical vent stack standing next to the soil stack
is not required. In one-story buildings, the upper extension
of the soil stack above the highest horizontal
drain connected to the stack becomes a vent called the
stack vent. It must extend 31 cm (12 in.) above the roof
surface, and should be kept away from vertical surfaces,
operable skylights, and roof windows.
When a sink is located in an island, as in some
kitchen designs, there is no place for the vent line to go
up. Instead, a waste line is run to a sump at another location,
which is then provided with a trap and vent. A
fresh-air vent, also called a fresh air inlet, is a short air
pipe connected to the main building drain just before
it leaves the building, with a screen over the outdoor
end to keep out debris and critters.
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