Protecting Your Property from Flooding: Sewer Backflow
Are You at Risk?
If you aren't sure whether your house is at risk from
flooding, check with your local floodplain manager, building
official, city engineer, or planning and zoning administrator.
They can tell you whether you are in a flood hazard area.
Also, they usually can tell you how to protect yourself and
your house and property from flooding.
What You Can Do
Flood protection can involve a variety of changes to your
house and property -- changes that can vary in complexity and
cost. You may be able to make some types of changes yourself.
But complicated or large-scale changes and those that affect
the structure of your house or its electrical wiring and
plumbing should be carried out only by a professional
contractor licensed to work in your state, county, or city.
One example of flood protection is installing a backflow valve
to prevent sewage from backing up into your house. This is
something that only a licensed plumber or contractor should
Install Sewer Backflow Valves
some floodprone areas, flooding can cause sewage from sanitary
sewer lines to back up into houses through drain pipes. These
backups not only cause damage that is difficult to repair but
also create health hazards.
A good way to protect your house from sewage backups is to
install backflow valves, which are designed to block drain
pipes temporarily and prevent flow into the house. Backflow
valves are available in a variety of designs that range from
the simple to the complex. The figure shows a gate valve, one
of the more complex designs. It provides a strong seal, but
must be operated by hand. So the effectiveness of a gate valve
will depend on how much warning you have of impending
flooding. Among the simpler valves are a flap or check valves,
which open to allow flow out of the house but close when the
flow reverses. These valves operate automatically but do not
provide as strong a seal as a gate valve.
Keep these points in mind if you have backflow valves
- Changes to the plumbing in your house must be done by a
licensed plumber or contractor, who will ensure that the
work is done correctly and according to all applicable
codes. This is important for your safety.
- Some valves incorporate the advantages of both flap and
gate valves into a single design. Your plumber or
contractor can advise you on the relative advantages and
disadvantages of the various types of backflow valves.
- Valves should be installed on all pipes that leave the
house or that are connected to equipment that is below the
potential flood level. So valves may be needed on washing
machine drain lines, laundry sinks, fuel oil lines, rain
downspouts, and sump pumps, as well as sewer/septic
- If you have a sump pump, it may be connected to
underground drain lines, which may be difficult to seal
Having a plumber or contractor install one backflow valve
will cost you about $525 for a combined gate/flap valve or
about $375 for a flap valve. These figures include the cost of
excavation and back-filling.
Other Sources of Information
Building Utilities from Flood Damage,
FEMA -348, 1999
To obtain copies of these and other FEMA documents, call
FEMA Publications at 1-800-480-2520. Information is also
available on the FEMA
- Protecting Your Home from Flooding, FEMA, 1994
- Repairing Your Flooded Home, FEMA-234, 1992
- Flood Emergency and Residential Repair Handbook, FIA-13,
- Retrofitting Flood-Prone Residential Structures,
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