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Sewer Backup
As shown in basement
plumbing, the
sanitary sewer line
drains toilet waste,
laundry tubs, and
(sometimes) the
basement floor drain
to the sanitary
sewer main in the
street. Clean
stormwater and
groundwater is
handled by
downspouts, footing
drains, and sump
pumps.
Often basement
flooding is caused
by these two sewer
systems being
interconnected.
 Some
houses have the
downspouts, footing
drain, and/or the
sump pump connected
to the sanitary
sewer service.
During a heavy rain,
stormwater enters
the sanitary sewers,
causing backups into
one house and
overloading the main
lines, contributing
to backups in other
houses.
Sewer backups can
also be caused by
events not related
to storms or
flooding. Individual
service lines can be
plugged by grease,
waste, tree roots,
breaks in the pipe,
or saturated ground.
Proper maintenance,
like pouring tree
root killer down the
toilet or floor
drain can prevent
most of these
problems.
The sewer mains can
also be plugged by
the same causes, or
by vandalism or
illegal dumping in
manholes. These
problems can be
fixed by the owner
or the Village,
depending on where
the stoppage occurs.
There are four ways
to stop sewer backup
that occurs when the
sewer main is
overloaded and backs
up through the
sanitary service
line into the house:
floor drain plug,
floor drain
standpipe, overhead
sewer, and backup
valve. Each of these
measures work for
buildings with
basements or
below-grade floors.
Floor Drain Plug
The simplest way to
stop sewer backup is
to plug the opening
where it first
occurs (see the
basement plumbing
graphic). This is at
the floor drain, the
sanitary sewer
system’s lowest
opening in the
house. Two
inexpensive measures
can be used: a plug
or a standpipe. Both
can be purchased at
local hardware
stores and are easy
for the handyperson
to install.
The flood drain plug
stops water from
flowing in either
direction.
Therefore, if the
laundry tub
overflows or other
spillage occurs, it
will stay in the
basement unless the
plug is removed.
Because of this, it
may be best to leave
the plug out under
normal circumstances
and put it in place
only during heavy
rains.
One variation is a
plug with a float.
It allows water to
drain out of the
basement (see
illustration, left
side). When the
sewer backs up, the
float rises and
plugs the drain (see
illustration, right
side). A float plug
permanently
installed will not
interfere with the
floor drain’s normal
operation.
Precautions:
A plug left in the
floor drain may
contribute to a wet
basement if water
from a laundry tub
spill or a leaky
pipe cannot drain
out. Float plugs are
known to have been
jammed open by a
small amount of
debris. A plug does
not tell you if
there is a problem
in your sewer
service line. If the
plug is not tight
enough, pressure can
eject it. Therefore,
a plug is not
recommended for
flood depths greater
than one foot.
Standpipe
A standpipe is
an inexpensive
alternative to a
floor drain plug.
When the sewer backs
up, the water moves
up the pipe. If
properly installed,
water pressure
cannot build up to
blow a standpipe out
of the floor drain.
The system works
unless the backup is
so deep that it goes
over the top of the
pipe.
Precautions:
Neither the plug or
standpipe stops
backup from coming
out of the next
lower opening, like
a laundry tub or
basement toilet.
Sealing the base of
the toilet to the
floor will protect
you until the water
backs up higher than
the top of the bowl.
Because water
pressure depends on
the height of water
in the pipes, a
standpipe does not
reduce the pressure
in the pipes (or
under the floor, if
the pipes leak).
Because the pressure
under the floor is
the same with a
standpipe or a plug,
standpipes and plugs
are only recommended
for flood depths of
one foot or less and
for buildings with
cast iron sewer
lines underneath the
floor.
Sewer Backup
Valve
A backup valve stops
the water in the
sewer pipes. While
not as foolproof as
an overhead sewer,
installation is less
disruptive to the
basement.
Older versions of
this approach were
located in the
basement floor and
relied on gravity to
close the valve. If
debris got caught in
the flapper, the
valve did not close
tight. Because of
its unreliability,
valves were
discouraged and even
prohibited in some
communities. Today’s
systems are more
secure. They include
installing two
valves in line,
using better, more
watertight
materials, or
counterweights that
keep the valve open
all the time so
debris won’t catch
and clog it.
Larger valve systems
are usually
installed in a
manhole in the yard,
well away from the
basement wall, so
there is less
disruption during
construction and no
concerns over
breaking the pipes
under the basement
floor. The cost of
this type of backup
valve is comparable
to the cost of an
overhead sewer, in
the $4,000 to $6,000
range.
Precautions:
The ejector pump and
the valve require
maintenance.
This work
requires a licensed
plumber.
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