What is the difference between sewer backup coverage and flood insurance for apartments?

Sewer backup and flood are distinct perils with different coverage mechanisms, and confusing them is a common and costly mistake for apartment owners. Flood insurance, whether through the NFIP or a private carrier, covers direct physical damage from the overflow of inland or tidal waters, mudslides, unusual and rapid accumulation of surface waters, and storm surge. The FEMA NFIP Flood Insurance Manual defines flood as 'a general and temporary condition of partial or complete inundation of normally dry land areas from overflow of inland or tidal waters or unusual and rapid accumulation or runoff of surface waters from any source.'

Sewer and drain backup coverage, available as an endorsement to the commercial property policy, covers water that enters the building through the building's own sewer, drain, or sump pump systems. This can occur because of a blockage in the building's plumbing, a failure in the municipal sewer system, or an overwhelmed storm drain that backs up into the building through connected pipes. The ISO Sewer Backup endorsement (CP 10 38) or equivalent proprietary endorsements provide this coverage.

The distinction matters most during heavy rainfall events. If rainwater overwhelms the storm sewer and backs up into the building through the building's drains, the loss is a sewer backup claim (covered by the sewer backup endorsement). If the same rain causes a nearby river to overflow and floodwater enters the building through doors and windows, the loss is a flood claim (covered by the flood policy). Both events can occur simultaneously during the same storm, splitting the loss between two different coverages with different limits and deductibles. Apartment owners in areas with combined sewer systems should carry both flood insurance and sewer backup endorsements with adequate limits.