The first portion of this message was posted by mistake, this is a
The floor drain plug might also cause backups in basement toilets,
laundry sinks or other basement drains. None of the homes affected
in my town had backups affecting anything besides the basements.
After learning about this problem, the only way I would have ever
allow a basement toilet in my residence is if there were a highly
reliable downstream backup prevention device in place.
Otherwise, what would have been most helpful would have been a
passive floor drain mechanism which can easily be retrofitted, and
that, left in place, would allow the floor drain to work except when
back pressure in the sewage line increased, at which point it would
There is only one product I was able to find after an extensive
search using Google, and it was far back in a long series of web
pages. The product is "Flood-guard" (R), made by General Pipe
Cleaners of McKees Rocks, PA, see their web site at
http://www.drainbrain.com , photos and complete explanations available
at the site.
One of their Flood-Guard devices is a check valve that is rammed
into the floor drain opening, then expanded with a stainless steel
screw/rubber donut mechanism to hold it in place. There is a float
in the center which rises when the downstream pressure does, and
blocks backflow. It comes in 2", 3" and 4" sizes. The cost is
about $10. Each floor drain would need one of these.
The company advises that the check valve device could be popped
out of its pipe if the pressure were high enough. In cases like
that, they also have a "stand-pipe" model, which uses the same
stainless steel screw/rubber donut mechanism, but with a pipe threaded
center to allow a standpipe to be screwed into the device. The
height of the standpipe determines the amount of protection provided.
There are two risks to standpipe use: (1) once the level of pressure
pushes the sewage to the top of the standpipe, it will overflow and
sewage backflow into the basement will occur. Unless there is an
alternate way of draining the basement, such as a sump pump, the
backflow cannot drain passively from the basement once the downstream
pressure falls. An standpipe which overflows will actually trap any
backflow on the basement floor until removed. (2) The height of the
standpipe determines the maximum pressure downstream before overflow
occurs. Some homeowners' sewer pipes could conceivably rupture under
their basement floors, were this to occur. It is hard to conceive
that a 3 to 7 foot head of water pressure would cause most commonly
used sewer pipes to rupture. The Flood-guard standpipe mechanisms
come in 3 and 4 inch sizes.
Unfortunately my floor drain opening (the bell of a 4" cast iron
sewer pipe of the 1950's) is incompatible with any of the Flood-guard
mechanisms - too big for 3" and too small for 4".
(End part 2, part 3 to follow)
One other danger of a sewer plug or standpipe is if you have
clay tile pipes under the floor instead of cast iron. They are
found in older houses (40 or 50 years or older). During a
backup the joints will leak causing hydraulic pressure under the
floor. The floor will try to float and could break up. As far
as back pressure causing the pipe to rupture, it's not likely.
The pressure, even from a 8' head, is not that great, still far
less than 1 psi.
Art beat me to it. <g>
There is indeed danger of lifting the entire basement slab when
a drain plug or a standpipe is used.
The joints in clay drain pipe are notoriously leaky and even a
small backpressure will cause many substantial leaks under the slab.
If you are there at the time of the backup, you can actually hear
the joints spitting water.
Assume a slab which is 10' X 10'. That's 100 sq ft, which is
14,400 sq in. Now, lets say that there is only 1/2 PSI of
pressure in the backed up sewer. If the leaky tile has flooded
under the entire slab (quite possible), the force trying to lift
the slab is over 7,000 Lbs !!! While that may not actually
float the thing, it usually results in very nasty cracks.
(BTW, the pressure developed by a head of water is closer to
1/2 PSI per foot of head. So, 8 Ft of head will give you
roughly 4 PSI.)
Actually, I had it on my calculator but didn't post the number;
I thought under 1 PSI was sufficient. But for the purists, it
is 0.29 PSI for an 8' head, water, of course. But, as Speedy
Jim points out, all those square inches add up real fast.
Speedy Jim wrote:
You have a typo. It's 8 *inches* of water, not 8 feet,
which produces .29 PSI.
8 foot of head gives 3.46 PSI.
See this instant chart:
Art Todesco wrote:
I'm still working on part 3 of 3.
The references I found about standpipes in floor drains did mention the
possibility of leakage under the slab due to leakage from the sewer pipe
joints, including heaving of the floor. I noticed my floor drain is part
of a cast iron pipe system & I can only assume the rest of the drain to the
city sewer is the same material. I wonder how common basement floor
heaving is versus the damage caused by sewage backflow, which is in our
local media many, many times annually. The concrete basement floor must
weigh several thousand pounds on its own.
Other references advised not to use standpipes higher than 3 feet from
the basement floor. The reasoning was that concrete block walls that make
up most basements can endure up to 3 feet on their outside surface, above
that level, they tend to cave in, which could result in a collapsed house.
So, it would be better to allow sewage to pour into one's basement when the
backup pressure exceeds 3 feet of water (and equalize the pressure from
inside to outside) rather than have the basement walls collapse. I'm a
doctor, not an engineer, but that makes sense. This is the reasoning that
also supports the gradual pumping-out of a totally flooded basement, since
too-rapid draining could also cause the basement walls to cave in. If the
basement is <= 3 feet of water in it, it's OK to pump it out as fast as
My 3 foot standpipe would, if filled, mean a back pressure of 1.3 psi,
per your reference. for a 100 sq. ft. slab, the underpressure could be as
much as 18,720 lb. If my concrete floor weighs 145 lb/cu ft and is 3
inches thick, a 100 sq ft slab weighs 3625 lb.
When I learned that the Flood-Guard wouldn't fit my cast iron floor
drain, I used a standpipe instead: Home Depot has variety of rubber donuts
one of which fitted precisely into the bell of my cast iron floor drain, and
allowed me to leave the iron grate inside the mechanism to keep solids out
of the drain. The inner diameter of the donut is a precise fit for 4" Sch.
40 PVC DWV, which is gently pounded in with the help of a 2 x 4 and a
hammer. The fit is very tight, appears leakproof, and the mechanism can be
disassembled for servicing by wiggling it free. My washing machine drain
hose hooks over the top of the standpipe, and is held in place with wire to
prevent it from whipping free. I understand some modern washing machines
drain themselves extremely rapidly, but mine isn't one of those. The cost
of my setup was $11. Now a Flood-guard would fit in the PVC pipe, but
the structure would start to resemble a water-propelled rocket, so I will
leave my standpipe as is.
I had to disconnect my laundry tray to install the standpipe, but it was
a small price to pay for peace of mind.
I am considering reattaching the laundry tray drain to the standpipe
using a Y of some sort and a rubber sleeve, and putting a gate valve into
the laundry drain, which would be left normally closed unless the tray was
actually in use. The function of the standpipe would be unchanged. I
could also install a laundry tray electric sump system to pump the tray out
to the top of the standpipe, or even to a higher level, HD's price was $165
and a 4-week wait for the special order.
The other two items that used to go into the floor drain are the
central A/C condensate, and the basement dehumidifier condensate, but my
plumbing inspector told me it was OK to drain these into the sump pit for
pumping into the street. I understand there are small pumps available to
put the A/C condensate anywhere desired, but gravity is OK for me, and the
sump pit will be very close to where the floor drain/standpipe is now.
HomeOwnersHub.com is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here.
All logos and trade names are the property of their respective owners.