INSTALL SEWER BACKFLOW VALVES
Protecting Your Property from Flooding
FEMA
April 2008

In some floodprone areas, flooding can cause sewage from sanitary 
sewer lines to back up 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 property from sewage backups is to 
install backflow valves, which are designed to block drain pipes 
temporarily and prevent return flow. 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. The 
effectiveness of a gate valve will depend on how much warning you 
have of impending flooding. 

Among the simpler valves are flap or check valves, which open to 
allow flow out of the structure but close when the flow reverses. 
These check valves operate automatically but do not provide as 
strong a seal as a gate valve. 

BENEFITS OF UTILIZING THIS MITIGATION STRATEGY

* Helps to prevent damage to a structure

* Helps to protect the health and safety of the structure’s 
occupants 

TIPS 

Keep these points in mind if you have backflow valves installed: 

* Changes to the plumbing in your property 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 structure 
or that are connected to equipment that is below the potential flood 
level. Therefore, valves may be needed on washing machine drain 
lines, laundry sinks, fuel oil lines, rain downspouts, and sump 
pumps, as well as sewer/septic connections. 

* If you have a sump pump, it may be connected to underground drain 
lines, which may be difficult to seal off. 

ESTIMATED COST 

Having a plumber or contractor install one backflow valve will cost 
approximately $1,400 for a combined gate/flap valve or about $600 
for a flap valve. These figures include the cost of excavation and 
backfilling. 

OTHER SOURCES OF INFORMATION 

FEMA 348, Protecting Building Utilities from Flood Damage, November 
1999, http://www.fema.gov/library/viewRecord.do?id=1750. 

FEMA 499, Home Builder's Guide to Coastal Construction, Technical 
Fact Sheet No. 29, August 2005, 
http://www.fema.gov/library/viewRecord.do?id=1570.  

To obtain copies of FEMA documents, call the FEMA Publications 
Warehouse at 1-800-480-2520 or visit FEMA’s Library online at 
http://www.fema.gov/library.