Why do basements flood in Washington, DC rowhouses and homes?
Many District rowhouses and older homes have full basements built long before modern waterproofing. Foundation walls of brick or old concrete can seep during heavy rain, and floor drains can back up. Some basement units, often called English basements, sit partly below the street, which leaves little margin when water rises outside.
The area also gets intense summer thunderstorms and the remnants of tropical storms. Gutters, downspouts and yard grading that send water toward the foundation make seepage worse. In some older neighborhoods, the public sewer system is a combined system that carries both storm water and sewage, and heavy rain can cause backups. That varies by street, so ask your utility if you are unsure.
Sump pumps help, but they fail. Power loss during a storm, a stuck float switch or a pump that is simply worn out can all let water in.

