they are also invaluable to renovators.
fitting or replacement pipe section, unroll the
2-in. copper vent pipe, and a 2-in.
For example, if you want to add a plastic
cast-iron takeoff on a 2 by 3 wye
neoprene sleeves onto the fitting or pipe, and
shower drain to a cast-iron stack, no-hub cou-
fitting. The other couplings join 3-in. tighten the steel band clamps. You can also tie
plings can accept either a cast-iron or a plastic
no-hub cast-iron fittings.
into a cast-iron drain without cutting into it by
no-hub fitting and seal it tightly to the pipe
building out from an existing cleanout, as shown
ends once you’ve cut into the stack. (support
in “Extending a Cast-Iron Main Drain” on p. 340.
P R O T I P
both sides of the section to be cut out so it can’t
Venting Options
shift during cutting and weaken other joints.)
When joining dWV pipes of different materi-
If you smear liquid soap on
Until you expose the framing and actually run
als, use specialized transition couplings whose
the outside of cast-iron pipes
the pipe, it’s difficult to know exactly how things
and no-hub fittings, you’ll have
neoprene sleeves are sized for incoming pipes
will fit together—especially vents. Because cor-
an easier time pulling the neo-
with different outside diameters, such as the
rect venting is crucial, this section discusses sev-
prene sleeves onto them.
coupling used to join 2-in. copper and 2-in. cast
eral venting options. But first, here are a few
iron, shown in the bottom photo at left.
terms to keep straight: A stack is a vertical pipe.
If the stack carries wastes, it’s a soil stack. If the
334 Chapter 12
side of a drainpipe: If it did, it could become
clogged with waste.
maximum Distance:
Branch vents must rise to a height of at least
Trap arm to vent* 42 in. above the floor before beginning their hori-
zontal run to the vent stack. This measurement
TRaP aRm
maXImum dIsTaNce
adds a safety margin of 6 in. above the height of
dIameTeR (in.)
To VeNT
the highest fixture (such as a sink set at 36 in.),
so there is no danger of waste flowing into the
11⁄4
2 ft. 6 in.
vent. Since branch vents run to a vent stack, they
11⁄2
3 ft. 6 in.
should maintain an upward pitch of at least 1⁄4 in.
per ft., although the UPC allows a vent to be level
2
5 ft.
if it is 6 in. above the flood rim of a fixture.
3
6 ft.
sTaCk venTIng
4
10 ft.
Clustering plumbing fixtures around a central
* Also maximum distance of stack-vented fixture trap arm
stack is probably the oldest method of venting. In
to stack, based on calculations found in the UPC, T10-1.
the early days of indoor plumbing, plumbers
noticed that fixtures near the stack retained
water in their traps while those (unvented) that
were at a distance did not. You can vent three
bathroom fixtures (lavatory, tub, and toilet) off a
3-in. stack vent, without additional branch
zzzzzz Back venting
(Continuous venting)
vents—if you detail it correctly, as shown in
“Stack Venting” on p. 336.
3-in.
Note: When stack venting, never place a toilet
stack vent
above the other fixtures on the stack: Its greater
discharge could break the water seals in the traps
of small-dimension pipes. If you must add fix-
tures below those already stack vented, add (or
11/2-in.
2-in.
extend) vent stacks and branch vents. The maxi-
branch vent
vent stack
mum allowable distance from stack-vented fix-
tures to the soil stack depends on the size of the
minimum Drain, Trap, and vent sizes
2-in.
branch vent
3-in.
FIXTuRe/aPPLIaNce
dRaIN/TRaP sIze
VeNT sIze
soil stack
Toilet
3 in. or 4 in.
2 in.
Bathtub/shower
2-in. drain; 11⁄2-in. trap
11⁄2 in.
shower stall
2 in.
11⁄2 in.
Lavatory
11⁄2-in. drain; 11⁄4-in. trap
11⁄4 in.
3-in.
Paired lavatories
2-in. drain; 11⁄2-in. trap
11⁄2 in.
main drain
Bidet
11⁄4 in.
11⁄4 in.
kitchen sink (with or without disposer) 11⁄2 in.
11⁄2 in.
dishwasher
11⁄2 in.
11⁄2 in.
In this illustration of back venting, all
fixtures have a dry branch vent—that is,
Laundry tub
11⁄2 in. or 2 in.
11⁄2 in.
no vent ever carries water. The fixtures
clothes washer standpipe
on the first floor require a 2-in. branch
2 in.
11⁄2 in.
vent because the toilet’s 3-in. drain
needs more incoming air to equalize its
large waste flow.
plumbing
335
pipe serving a particular fixture (see “Maximum
Distance: Trap Arm to Vent” on p. 335).
zzzzzz stack venting
venTIng ToIleTs
3-in. stack
3x11/2
sanitary tee
Because they have the biggest drain and vent
11/2-in.
p
CONSTRICTED SPACES ipes of any fixture, toilets can be the trickiest to
lav. drain
When a branch dr v
ai enn t
m . uW
st htreanv esl ptahcre
o ubgehn
ae a
fl toho ra ptloatilfeotr ims bneofto rae prero ac bh-ing a stack, the drain must slope gradually.
Here, the angle the vent takes off from the toilet drain is critical—it must not be less than 45 degrees, as depicted lem, use a setup such as the one show
in the accompanying cross-section drawing.
in “Venting a Toilet,” in which a 2-in. vent pipe
Closet flange
43 closet bend
rises vertically from a 3 by 2 combo, while the
3-in. toilet drain
3-in. drain continues on to the house main. The
32 combo
3-in.-dia. toilet drain allows the vent to be as far
Min. 45 degrees
2-in. vent
as 6 ft. from the fixture, as indicated in the table
on p
. 335.
11/2-in.
tub drain
When space is tight, say, on a second-floor
bathroom with finished ceilings below, the drain
and vent pipes must descend less abruptly (see
Side-inlet tee
3-in. toilet drain
“Constricted Spaces” below). Here, the critical
4x3 closet bend
detail is the angle at which the vent leaves the
3 by 2 combo: That vent takeoff must be 45° above
a horizontal cross section of the toilet drain. If it
If close enough to a stack vent of adequate size, fixtures can
is less than that, the outlet might clog with waste
use it for venting (see “Maximum Distance: Trap Arm to Vent” on p. 335).
and no longer function as a vent. As important,
Note: The side inlet serving the tub enters above the toilet inlet;
the “horizontal” section of the vent that runs
this fixture group must be the highest on the stack.
between the takeoff and the stack must maintain
a minimum upward pitch of 1⁄4 in. per ft.
2-in. vent
zzzzzz venting a Toilet
zzzzzz Constricted spaces
2-in. vent
Closet flange
Closet flange
Minimum upslope of
1/4 in. per ft.
45° minimum
4x3 closet bend
4x3
3x2 low-heel vent or
closet bend
3-in. tee with 2-in.
bushing
3-in. toilet drain
3x2 combo
3-in. drain
3-in. combo
When a branch drain must travel through a
floor platform before reaching a stack, the
drain must slope gradually. Here, the angle
the vent takes off from the toilet drain is
When there’s plenty of space under a
critical—it must not be less than 45°, as
toilet—say, in an unfinished basement—
depicted in the cross-section drawing
the branch drain can descend steeply.
on the facing page.
336 Chapter 12
When you’ve got two toilets back to back, you
In addition to the fittings shown in the draw-
can save some space by picking up both with a
ing, note these factors as well: The loop must rise
single figure-5 fitting (double combo), like the
as high under the counter as possible and at least
small one in the bottom right photo on p. 333.
6 in. above the juncture of the trap arm and the
From the top of the fitting, send up a 2-in. or
sanitary tee to preclude any siphoning of waste-
3-in. vent; from the two side sockets use two 3-in. water from the sink. The vent portions may be
soil pipes serving the toilets; and use a long-sweep 11⁄2-in. pipe, but the drain sections must be 2 in.
ell (or a combo) on the bottom to send waste on
in diameter, and drain sections must slope down-
to the main drain. This fitting is about the only
ward at least 1⁄4 in. per ft.
way to situate back-to-back water closets and is
air-admittance valves (aaV) are one-way
quite handy when adding a half bath that shares
mechanical vents designed to eliminate the need
a wall with an existing bathroom.
for conventional branch vents for fixtures too far
from a wall. As water drains from a sink, it cre-
oTher venTIng opTIons
ates a partial vacuum within the pipes, depress-
ing a spring inside the AAV and sucking air in.
Common vents are appropriate where fixtures
When the water is almost gone and the vacuum
are side by side or back to back. This type of vent is equalized, the spring extends and pushes its
usually requires a figure-5 fitting.
diaphragm up, sealing off outside air once again
Loop vents are commonly installed beneath an
and preventing the release of sewer gases.
island counter in the middle of a room. The sink
Because fixture drains with AAVs don’t need lat-
drain is concealed easily enough in the floor plat-
eral vent runs or additional vent-stack penetra-
form, but the branch vent, lacking a nearby wall
tions in the roof, they allow greater design flexi-
through which it can exit, requires some ingenu-
bility, while saving considerably on labor and
ity. This problem is solved by the loop shown in
materials. Mechanical vents were once intended
“Venting an Island Sink” below.
Branch
zzzzzz vent-Takeoff Cross section
vent
zzzzzz venting an Island sink
Countertop
Wall
Section of
(flood rim)
horizontal drain
90° ell
45° ell
OK
11/2 in.
2 in.
Cleanout
P-trap
OK
45° minimum
Long-sweep
Sanitary tee
ell
Floor
Combo
11/2-in.
Cleanout
foot vent
No!
Combo
2-in. branch drain
Wastes
A looped vent is one code-approved way to vent an island sink.
The loop should extend as high as possible under the countertop.
Vents must take off from horizontal
Loop preassembly makes construction easier. The foot vent must
drains at a 45° angle minimum. If the
connect to the loop via a combo fitting and slope upward to the
takeoff angle is less than 45°, wastes
stack at a minimum of 1/8 in. per ft.
can block the vent.
plumbing
337
to be only temporary, but their valve mechanisms
have been improved so that air-admittance valves
gOiNg WiTH THe Flow
are now accepted by major building codes,
To optimize flow and minimize clogged pipes,
including the IRC.
follow these guidelines:
venT TermInaTIon
dRaINage FITTINgs. use a long-sweep ell
(90° elbow) or a combo when making a 90°
To reduce chances that vent gases will enter the
bend on horizontal runs of waste and soil pipe
home, stack tops must be at least 6 in. above the
and where vertical pipes empty into horizontal
upslope side of the roof and at least 3 ft. above
ones. use a standard ell when going from
any part of a skylight or window that can be
horizontal to vertical. Where trap arms join vent
opened. A vent stack must be at least 12 in. hori-
P R O T I P
stacks, use sanitary tees. (Long-sweep fittings
zontally from a parapet wall, dormer sidewalls,
and the like. Finally, stacks must be correctly
are not required on turns in vent pipe; regular
when ordering supplies,
flashed to prevent roof leaks.
tees and ells may be used there.)
order 20% more pipe than you
think you’ll need and at least
cLeaNouTs. cleanouts are required where a
a half-dozen extra of the more
buildi
ng main joins a lead pipe from a city sewer
Roughing-in DWV Pipes
common fittings such as tees,
line or septic tank, at the base of soil stacks,
In new construction, pros typically start the DWV
combos, ells, and couplings.
and at each horizontal change of direction of
system by connecting to the sewer lead pipe, sup-
you’ll also need straps and
45° or more. also, install cleanouts whenever
porting the main drain assembly every 4 ft. and
clamps to support pipe runs,
at each point a fitting is added.
as well as consumables such as
heavy flow increases the possibility of clogging,
Renovation plumbing is a different matter
solder or plastic-pipe cement and
such as in back-to-back toilets. There must be
altogether, unless an existing main is so corroded
plumber’s sand cloth. most supply
enough room around the cleanout to operate a
or undersize that you need to tear it out and
stores accept returns, but check
power auger or similar equipment.
their policy before ordering.
replace it. Rather, renovation plumbing usually
entails tying into an existing stack or drain in the
most cost- and time-effective manner. There are
three plausible scenarios: (1) cutting into a stack
to add a branch drain, (2) building out from the
end of the main drain where it meets the base of
pipe-support spacing the soil stack, and (3) cutting into the main drain
in midrun and adding fittings for incoming
PIPe maTeRIaL
HoRIzoNTaL suPPoRTs
VeRTIcaL suPPoRTs
branch drains.
This discussion assumes that the existing
Water supply
pipes are cast iron and that new DWV pipes or
copper
6 ft.
10 ft.
fittings are ABS or PVC plastic, unless otherwise
noted. If you’re adding several fixtures, position
cPVc
3 ft.
10 ft. and midstory guide
the new branch drain so that individual drains
PeX
32 in.
Base and midstory guide
can be attached economically—that is, using the
least amount of pipe and fewest fittings.
dWV
Remember, drainpipes must have a minimum
downward slope of 1⁄4 in. per ft.
4 ft. and at
10 ft. and midstory guides
aBs or PVc
branch connections
if pipe ≤ 2 in.
cast iron
5 ft.
Base and each story; 15 ft.
When splicing a branch to an existing
drain, support both sides of the
takeoff fitting. Here, J-clamps are on
both sides of a combo fitting.
Transition couplings join copper to
Renovation 4th Edition Page 78