Cold-water
Branch
trunk line
get to know the staff at a local
temperature- and pressure-relief (TPR) valves,
lines
plumbing-supply store. But visit
which keep water heaters from exploding, are
Risers
Hot-water
trunk line
the store during off-peak hours.
correctly rated and installed.
Service
The last thing counter clerks
pipe
need during the 8 a.m. rush is
duffers with dinky orders and a
million questions. when business
the service pipe. So it won’t freeze, a service pipe
Main supply pipe
is slow, however, most of these
must run below the frost line and enter a build-
clerks are happy to share what
ing through the foundation. Typically, a 1-in. ser-
they know.
vice pipe is controlled by a main shutoff valve
Water heater
shortly after it enters a building; municipal hook-
ups may enter a water meter first. Plumbing
codes also may require a pressure-reducing valve
if water pressure is more than 80 pounds per
square inch (psi).
Originating at a service pipe from the
On the other side of the shutoff valve, the ser-
street (or from a wel ), the main supply
vice pipe continues as the main supply pipe, com-
pipe splits at a T-fitting, with one leg
monly 3⁄4 in. in diameter. At some point, the main
feeding cold-water trunk lines and the
supply pipe enters a tee fitting where it splits.
other entering the water heater to
One leg continues on as a cold-water trunk line
emerge as the hot-water trunk line.
and the other feeds into the water heater, where
it emerges as the hot-water trunk line. From the
3⁄
and easily assembled with solvent cement. But it
4-in. hot and cold trunks run various 1⁄2-in.
branch lines that serve fixture groups. Finally,
may be cross-linked polyethylene (PEX) flexible
individual risers (supply tubes) run from branch
piping that will finally dethrone King Copper
lines to fixtures. Risers are 3⁄
(PEX is discussed later in this chapter).
8 in. or 1⁄2 in. in
diameter and connect to fixtures with threaded
In contrast to the trunk-and-branch distribu-
fittings. By decreasing in diameter as they get
tion common to rigid piping, flexible PEX tubing
farther from the trunk lines, supply pipes help
systems feature a 3⁄4-in. main water line that
maintain constant water pressure.
feeds into a manifold, out of which small supply
Before the 1950s, supply pipes were usually
lines run directly to fixtures. Because it doesn’t
galvanized steel, joined by threaded fixtures, but
rely on large pipes to distribute water, this home-
steel pipes corrode and corrosion constricts flow. run manifold system delivers hot water quickly to
Consequently, rigid copper piping, which cor-
fixtures, saving water and energy.
rodes more slowly, soon replaced galvanized
pipe. Joined by sweat fitting (soldering), copper
DraInage, wasTe, anD venTIng
was also easier to install and has been the domi-
The DWV system carries wastes and sewage
nant supply piping since the 1950s. Rigid plastic
gases away from the house.
pipe, especially chlorinated polyvinyl chloride
Every fixture has a drain trap designed to
(CPVC), has gained market share because it is
remain filled with water after the fixture empties.
corrosion resistant, less expensive than copper,
This residual water keeps sewage gases from
plumbing
317
rising into living spaces. (Toilets have integral
and whose upper leg is a branch vent. Branch
traps.) As trap arms leave individual fixtures,
vents continue upward, often joining other fix-
they empty into branch drains or directly into a
ture vents, until they join a vent stack, which
soil stack, which, at its base, turns and becomes
exits through the roof.
the main drain. The main drain then discharges
Because vents must admit enough air to offset
into a city sewer main or a septic tank.
that displaced by falling water, vents are approxi-
Drainpipes also may be differentiated accord-
mately the same size as their companion drains.
ing to the wastes they carry: Soil pipes and soil
Branch vents and drains are usually 11⁄2-in. or
stacks carry fecal matter and urine, whereas
2-in. pipes, and main stacks and drains are 3 in.
waste pipes carry wastewater but not soil. Stacks Minimums are indicated in “Minimum Drain,
are vertical pipes, although they may jog slightly
Trap, and Vent Sizes” on p. 335. Important:
to avoid obstacles.
Drainpipes must slope downward at least 1⁄4 in.
Venting is the “V” in DWV. Without venting,
per ft. so that waste will be carried out; vent
wastes would either not fall at all or, in falling,
pipes usually slope upward a minimum of
1
would suck the water out of fixture traps, allow-
⁄8 in. per ft.
ing sewage gases to enter living spaces. Vents
DWV pipes may be of any number of materi-
admit an amount of air equal to that displaced
als. An older house may have drain and vent
by the falling water. Thus every fixture must be
pipes with sections of cast iron, galvanized steel,
vented. In most cases, the trap arm exits into a
copper, or plastic. Because some of these materi-
tee fitting whose bottom leg is a branch drain
als also are used for supply, let size be your guide:
If an existing pipe’s diameter is 11⁄4 in. to 4 in., it’s
a drain or vent pipe. DWV pipes installed these
days are mostly plastic: white polyvinyl chloride
(PVC) or black acrylonitrile butadiene styrene
zzzzzz The Dwv system (Drainage,
waste, venting)
(ABS). A host of ingenious fittings enable the var-
ious materials to be connected tightly together.
Note: If sound suppression is an issue, you
Stack vent
should insulate plastic pipes or install cast iron.
Branch
2 in.
vent
Vent stack
zzzzzz a Drain Trap
11/2 in. 11/2 in.
2 in.
Vent
2 in.
Branch
drain
2 in.
2 in.
Soil stack
11/2 in.
3 in. minimum
Main drain or
Sanitary
To sewer or
building drain
tee
septic tank
Drain-trap
water seal
Drain
Drainpipes must slope downward at least
Water traps seal sewage gases from
1/4 in. per ft. so wastes can fall freely.
living spaces, but they need vents to
Vent pipes must slope upward at least
operate properly. Without incoming air
1/8 in. per ft. so sewage gases can rise
from the vent, fal ing wastes could suck
and exit the building.
the water out of traps.
318 Chapter 12
mounted ceramic tank with a standard (close-
Planning
coupled) unit, there could be an ugly gap
If you’ll be adding or moving fixtures, you’ll need between the toilet and the finish wall. By install-
to install pipes, and that will require permits and
ing a 14-in. rough toilet, whose base is longer, you
planning. Start by assessing the condition of
can use the existing floor flange and eliminate
existing pipes (see chapter 1), which you can con- the gap behind the toilet.
nect to if they are in good shape. Create a scale
Install water-supply risers on the wall behind
drawing of proposed changes, assemble a materi-
the toilet, 6 in. above the floor and 6 in. to the left
als list, and then ask a plumbing-supply store
of the drainpipe. If there’s a functional riser stick-
clerk or a plumber to review both. If you’re well
ing out of the floor, use it. But floor risers are sel-
organized, clerks at supply stores will usually be
dom installed today because they make mopping
glad to help. However, if you need help under-
the floor difficult. Clearances around bidets are
standing your existing system, hire a plumber to
the same as those for toilets.
assess your system. He or she can also explain
Lavatories and pedestal sinks should be a
how to apply for a permit and which inspections
comfortable height for users. Typically, lavatory
will be required.
rims are set 32 in. to 34 in. above the finish floor,
but if a family is tall, raise the lav. (If you do,
Is There enough room?
remember to raise drain and supply-pipe holes
If you’re adding a bathroom, first consider the
overall size of the room. If there’s not enough
space, you may need to move walls. Layouts with
pipes located in one wall are usually the least dis-
ruptive and most economical because pipes can
zzzzzz minimum Bathroom Dimensions
PIPES IN ONE WALL
PIPES IN TWO WALLS
be lined up in one plane. On the other hand, lay-
outs with pipes in three walls are rarely sensible
7 ft. 2 in.
7 ft. 2 in.
or feasible unless there’s unfinished space above
or below in which to run pipes.
FIxTure rough-In DImensIons
Once you have a general idea if there’s enough
room, focus on the code requirements for each
5 ft. 0 in.
5 ft. 0 in.
fixture, which dictate where fixtures and pipes
must go. It would be aggravating and expensive
if code inspectors insisted that you move fixtures
after finish floors and walls had been put in
PIPES IN THREE WALLS
place. So install fixtures and pipes to conform
with code minimums. The drawings on
8 ft. 6 in.
pp. 320–321 show typical drainpipe and supply-
pipe centers for each fixture and, in most cases,
minimum clearances required from walls, cabi-
nets, and the like.
On toilets, the horn—the integral porcelain bell
protruding from the bottom—centers in the floor
6 ft. 0 in.
flange. The flange, and the closet bend to which
it attaches, should be centered 12 in. from the
finish wall for most toilets or 121⁄2 in. from an
exposed stud wall. Codes require at least 15 in.
clearance from the center of the toilet to walls
FIVE FIXTURES
or cabinets on both sides: In other words, install
16 ft. 4 in.
toilets in a space at least 30 in. wide. There also
must be at least 24 in. of clear space in front of
the toilet.
Toilets with 10-in. and 14-in. rough-in dimen-
sions are available to resolve thorny layout issues
(such as an immovable beam underneath) or to
5 ft. 0 in.
replace nonstandard toilets. For example, if you
replace an old-fashioned toilet with a wall-
plumbing
319
Toilet Rough-in Dimensions
Center the toilet drain 12 in. from the finished wall behind the unit. Allow at least 15 in. clearance on both sides of the toilet, measured from the center of the drain.
1/2-in. water supply
Finished wall
12 in.
6 in.
15 in.
15 in.
Closet flange
Finished wall
zzzzzz Toilet rough-In Dimensions
zzzzzz lavatory rough-In
Dimensions 1/2-in.
water supply
1/2-in.
4 in. to 8 in.
water supply
11/2-in.
drain
6 in.
18 in.
24 in.
12 in.
15 in.
15 in.
Lavatory
centerline
Center the toilet drain 12 in. from the
finished wall behind the unit. Allow at least
Positioning supply pipes and valve stems is
15 in. of clearance on both sides of the toilet,
easier because they’re smaller and typically cen-
measured from the center of the drain.
tered on an end wall—although, again, follow the
manufacturer’s rough-in dimensions for code-
required pressure-balancing valves and the like.
an equal amount.) Codes require at least 18 in.
Place the shower arm 72 in. to 78 in. above the
clearance in front of a sink; 24 in. is better.
floor so taller users won’t need to stoop when tak-
Lavatory drains are typically 18 in. above the
ing a shower. Place the tub spout 22 in. high. Tub
floor and centered under the lavatory, although
faucet handles (and mixing valves) are customar-
adjustable P-traps afford some flexibility in posi-
ily 6 in. above the spout.
tioning drains. Center supply pipes under the
lav, 24 in. above the floor, with holes spaced 4 in.
Kitchen sinks frequently have double basins, so
on center. Pedestal sink drains are housed in
you can center or offset drainpipes. In a standard
the pedestal, so tolerances are tight; follow the
36-in.-wide base cabinet, the drain often is offset
manufacturer’s installation instructions when
so that it is 12 in. from one cabinet sidewall, leav-
positioning pipes.
ing room to hook up a garbage disposer. To make
cabinet installation easier, have the drain exit
Bathtubs and showers vary greatly, so follow
into the wall rather than the floor. A drain that
the manufacturer’s guides when positioning the
exits 15 in. above the finish floor will accommo-
pipes. Most standard tubs are 30 in. to 32 in.
/>
date the height of a garbage disposal (11 in.) and
wide and 5 ft. to 6 ft. long. Codes require a mini-
the average depth (9 in.) of a kitchen sink. Sink
mum of 18 in. clearance along a tub’s open
faucet holes are typically spaced 8 in. on center,
side(s); 24 in. is better.
so align supply pipes with their centerline,
Freestanding tubs have exposed drain and
roughly 2 in. above the drain height. Supply-pipe
overflow assemblies, so their 11⁄2-in. drains can
height is not critical because risers easily accom-
be easily positioned to avoid joists and other
modate varying heights.
design constraints. Standard tubs require a hole
approximately 12 in. by 12 in. in the subfloor
skeTChIng layouTs
under the tub drain end to accommodate the
drain and overflow assembly. If an existing joist
Make a separate sketch of each floor’s plumbing;
is in the path of the tub drain, you may need to
include the basement and attic, too. Start by cre-
cut through the joist and add doubled headers, as ating an accurate outline of the house’s footprint,
explained further on p. 341.
using graph paper and a scale of 1⁄4 in. per 1 ft.
320 Chapter 12
zzzzzz Tub/shower rough-In
Dimensions
zzzzzz kitchen sink rough-In
Dimensions
15 in.
1/2-in.
36-in.
shower arm
cabinet height
72 in. to 78 in.
1/2-in.
water supply
8 in.
Long wall
End wall
or pipe wall
12 in.
Mixing valve
1/2-in.
15 in.
12 in. or as
tub spout
or less 18 in.
desired
12 in.
22 in.
8 in.
11/2-in. drain
offset
15 in.
Double sinks are most often installed in
kitchens, so the drain is often offset under
one sink, as shown in the drawing on p. 348.
Braided stainless-steel supply lines are very
Tub width:
flexible, so you can rough-in water supply
30 in. to 32 in.
stub-outs at any convenient height; 18 in.
Tub length:
is common.
60 in. to 72 in.
The tub drain and stubs in the end wall should
be centered 15 in. from the long wall. Mixing
Framing Considerations
valves are typical y set 12 in. above the tub spout,
whereas individual valve stems are set 6 in. above
after positioning fixture drains, see if there’s a joist in the drain path. If there
the spout, 8 in. o.c., or follow the manufacturer’s
Renovation 4th Edition Page 74
