How to prevent basement flooding: sump pumps, backflow & drainage

Blue Arrow RestorationPublished September 21, 20266 min read

Many Long Island and Queens basements sit below street level, and heavy storms send water in through window wells, walls and floor drains. Here’s how sump pumps with battery backup, backwater valves, downspout extensions, grading and window well covers keep it out — plus the insurance endorsement most homeowners overlook.

In this guide

How water gets into a basement
Outside: grading, gutters and window wells
Sump pumps and backup power
Backwater valves
The insurance gap

How water gets into a basement

Surface water: rain running toward the house and pooling against the foundation
Groundwater: a rising water table pushing through slab cracks and the wall-floor joint
Window wells and exterior stairwells: drains clogged with leaves fill up like a tub
Sewer surcharge: the municipal sewer backs up and pushes water through floor drains

Outside: grading, gutters and window wells

Clean gutters in spring and fall; make sure downspouts discharge at least 4–6 feet from the foundation
Regrade soil so it slopes away from the house
Install clear window well covers and keep well drains clear
Clear the drain at the bottom of exterior basement stairs before storms
Seal visible foundation cracks and gaps around pipe penetrations

Sump pumps and backup power

A sump pump collects water that reaches the pit from drain tile or the soil below the slab and pumps it out. The weak point is power: storms that bring the most water also knock out electricity.

Test the pump every season by pouring water into the pit
Add a battery backup pump or a water-powered backup where allowed
Install a high-water alarm
Make sure the discharge line isn’t frozen or draining right back toward the house
Replace pumps older than about 7–10 years

Flooded basement on Long Island after a storm — Most of the flooded basements we see had a pump that lost power or failed during the storm.

Backwater valves

A backwater (backflow) valve on the building sewer lets wastewater out but closes when the street sewer surcharges. In neighborhoods with combined sewers, such as many parts of Queens, it can prevent sewage from coming up through basement drains. Installation generally requires a licensed plumber and may require a permit.

Inside the basement

Store valuables on shelves, not on the floor, and in plastic bins rather than cardboard
Consider tile or luxury vinyl instead of carpet
Run a dehumidifier in summer and keep humidity under about 50%
Keep furnaces, water heaters and electrical panels raised where possible

The insurance gap

Standard homeowners policies generally exclude flood and water that backs up through sewers or drains. The fix is usually two separate products: a water/sewer backup endorsement on your homeowners policy, and a flood insurance policy for surface water. Ask your agent what limits you have — backup endorsements often carry modest limits. More: Does insurance cover water damage?

Already flooded? See flood cleanup and sewage cleanup.