Preventing basement flooding in New York City is mostly about the sewer, the gutters and the ground around the house. You cannot stop a cloudburst, but you can make it much less likely that the water ends up in your basement. Here is a short checklist, built on what the Department of Environmental Protection and FloodHelpNY tell homeowners.
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Why basements flood in NYC
DEP names four kinds of flooding in the city: street flooding from blocked catch basins, coastal flooding from high tide and surge, groundwater coming through foundation cracks or a leaking floor drain, and sewer backups when heavy rain exceeds the pipes’ capacity. During Ida, NYC Health reports, rain fell at up to 3.5 inches an hour in places, against a sewer capacity of 1.75 inches an hour. NYC Health’s point is that rainfall flooding can happen anywhere in the city.
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The checklist
Disconnect your downspouts
This one is the law. DEP says it is mandatory for homeowners to make sure their downspouts are disconnected from the city’s sanitary sewer, because those connections can overwhelm the sewer with rainwater and cause sewer backups in basements. Redirect the water at least 6 feet away from the foundation. Non-compliance may result in fines.
Ask a plumber about a backwater valve
A backwater valve on the sewer line closes when sewage tries to flow back in. FloodHelpNY lists the common types, gate, ball and flapper valves (also called check or duckbill valves), and says a licensed plumber or engineer can tell you which, if any, suits your home. It also lists the communities in its Residential Backwater Valve Installation Program: Lower Manhattan, Rockaway East, Southeast Brooklyn Waterfront, Gravesend and Bensonhurst, Howard Beach, Gerritsen Beach and Sheepshead Bay, and the Southern Brooklyn Peninsula. Check with FloodHelpNY whether it is taking applications.
Report clogged catch basins
DEP cleans and maintains about 150,000 catch basins and asks residents to report a clogged one to 311. A catch basin full of leaves on your corner is a street flood waiting for the next storm. Report it before the rain, not during.
Read Rainfall Ready
DEP publishes “Rainfall Ready: A Homeowner’s Guide” in 12 languages, with tips to protect a home from flooding and sewer backups. It is worth reading once and keeping.
Look after the ground and the openings
As general practice: keep the ground sloping away from the foundation, keep areaway and stair drains clear, cover or raise low window wells, and seal gaps at basement doors. Small seepage through cracks can be sealed; anything bigger is for a waterproofing contractor. The basement waterproofing guide goes through the options.
Store things off the floor
Keep boxes, papers and anything you cannot replace on shelves, not on the basement floor, and in plastic bins rather than cardboard. “The key to mold control is moisture control,” the EPA says: a dry basement is far less likely to grow mold.
Know your zones
Look up the FEMA flood zone and the NYC evacuation zone for your address. NYC Flood Maps describes the high-risk area as a 1% chance of flooding in any year and 26% over a 30-year mortgage; NYC Emergency Management ranks six evacuation zones by surge risk. NYC Health also reports a 200% increase in high tide flood days from 2000 to 2021. The NYC flood zones guide explains how.
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Bigger changes
Some owners consider filling in a basement after repeated floods. FloodHelpNY notes that this needs an engineer and a permit from the Department of Buildings. If anyone lives in the basement, the first priority is getting out safely when water comes in: see the post on basement apartment flooding.
If the basement has already flooded, start with basement flooding in NYC.
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Questions people ask
Where do I start with preventing basement flooding in NYC?
Start with what DEP requires: disconnect downspouts from the sanitary sewer and send the water at least 6 feet from the foundation. Then ask a plumber or engineer whether a backwater valve suits your home.
Can a backwater valve stop basement flooding?
It is designed to stop sewage flowing back in through the sewer line, not groundwater or street water. FloodHelpNY says a licensed plumber or engineer can tell you which type, if any, suits your home.
Who do I tell about a blocked catch basin?
311. DEP maintains about 150,000 catch basins and asks residents to report clogged ones.
NowWater in the building?
Tell us where and what happened, and an independent local provider can contact you.