Not All Backwater Valves Are Equal
Some types of backwater valves, such as the plug type, are not recommended. While they may prevent water from entering your basement, they allow sewer backup pressure to build beneath your basement floor. This can potentially cause structural damage to your home.
Insurance and Backflow Valves
Depending on where you live and the prevalence of sewer flooding events, your insurer may require you to install a backflow valve. If you have suffered substantial sewer backup damage, the installation of a back water valve may be required to maintain insurance coverage. Some municipalities offer rebates to encourage installation of these preventive devices. For more information on how installing a backwater valve can help with your home insurance premiums, contact your insurance broker or agent.
Source:
Handbook for Reducing Basement Flooding, Institute for Catastrophic Loss Reduction