Basement finishing in New York City

Cost vs. Value's 2025 report put a basement remodel in the New York market at $61,417¹, above the $52,012² national average. The biggest local factor is water: the Comptroller's office estimated 424,800³ basements and cellars in the city's one- to three-family homes, and 43,000³ of them already facing some flood risk.

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Updated October 12, 2026

Illustration of the basement of a 1920s brick two-family row house in Ridgewood, Queens being finished, with foam board and stud walls along the brick foundation, a new backwater valve set in a trench in the floor and gas meters in a framed utility room. — Illustration

What a finished lower level costs here

Cost vs. Value's standard basement job adds a family room, a wet bar and a small full bath. Its 2025 New York figures run above the national cost, while local agents expected a smaller share back at sale.

Measure	New York market	U.S. average
Basement remodel, job cost	$61,417¹	$52,012²
Basement remodel, resale value	$35,572¹	$36,905²
Basement remodel, cost recouped at resale	58%¹	71%²

Cost vs. Value's basement job finishes a 20-by-30-foot lower-level entertaining area with a wet bar and a 5-by-8-foot full bathroom, with insulated exterior walls, painted drywall walls and ceilings, an enclosed mechanical area and snap-together laminate flooring.⁴ City lower levels are often smaller and lower than that, and flood protection, a backwater valve or a new escape window all come on top.

Basements, cellars and flood risk

The Comptroller's office counted lower levels in one-, two- and three-family homes across the five boroughs and mapped them against flood risk. Its estimate dates from 2022, and we found no newer citywide count.

Measure	New York City
Basements and cellars in one-, two- and three-family homes (estimate)	424,800³
Basements and cellars in one- to three-family homes now facing some flood risk (estimate)	43,000³

When the remnants of Hurricane Ida struck in 2021, 13 New Yorkers died, and 11 of them drowned in basement apartments in Queens and Brooklyn.³ Since then the city has kept basement and cellar apartments out of its highest flood-risk areas, so check your lot before planning a finished room, let alone a separate unit.

Downpours and freezes

Central Park's and LaGuardia's normals both show a steady run of days with an inch or more of rain, the storms that overload sewers, along with a long season of freezing nights.

Measure	Central Park	LaGuardia Airport
Days a year with an inch or more of rain or melted snow	14 days⁵	12 days⁵
Days a year with a low at or below freezing	67 days⁵	62 days⁵

The same guide calls directing roof water away from the foundation walls critical to a dry basement, and recommends cleaning gutters, connecting downspouts to proper drains and sealing cracks in foundation walls.⁶ Do those before paying for interior drains or a new floor.

Houses with a lower level

The Census Bureau doesn't count basements, so building type is the nearest local measure. Queens, the comparison borough, has more detached houses and more two- to four-family buildings than the city overall.

Measure	New York City	Queens County
Single-family detached homes	9%⁷	19%⁷
Homes in buildings with two to four units	21%⁷	30%⁷

A Queens two-family's lower level is usually where the gas meters, the boiler and the laundry for both households sit. Keep clear access to all of it in the finished layout, and plan the work around a tenant who still needs heat and hot water.

Foundations from before the war

Most homes in the city and in Queens went up before 1960, and a lower level that old has usually been patched, painted and re-piped more than once.

Measure	New York City	Queens County
Homes built before 1960	60%⁸	63%⁸
Homes built before 1940	38%⁸	30%⁸

Building America advises keeping fiberglass batts and cellulose out of contact with foundation walls, and not putting polyethylene sheeting, vinyl or foil wallpaper, or epoxy, oil or alkyd paint on the inside of basement walls, because they trap moisture.⁹ Ask what will sit against the brick or block, and how it handles moisture, before any framing goes up.

Permits

Finishing a basement is permit work at the Department of Buildings, with plans filed by a registered architect or engineer and the plumbing and wiring under licensed trades. Whether the space is a cellar or a basement, measured against the curb, decides whether anyone may live in it. A separate apartment below grade is an ancillary dwelling unit with its own ceiling, escape-window and sprinkler rules, and it can't go in the city's high-risk flood areas.

The majority of construction in New York City needs a DOB permit, and the plans must be filed by a New York State registered architect or licensed professional engineer, who submits the application and drawings.¹⁰
Under the Multiple Dwelling Law, a cellar is an enclosed space with more than half of its height below the curb level, and it does not count as a story.¹¹
A basement, by the same law, is a story partly below the curb level but with at least half of its height above it.¹²
Under the state Multiple Dwelling Law, residential use is prohibited in cellars but allowed in basements, so whether a lower level counts as a cellar or a basement decides whether anyone may live in it.³
DOB's ADU rules require at least 7 feet of ceiling height in every habitable room, and a cellar's ceiling must be at least 2 feet above grade.¹³
Basement and cellar ADUs are not permitted in the city's high-risk flood areas: FEMA's Special Flood Hazard Area, the Coastal Flood Risk Area and DEP's 10-Year Rainfall Flood Risk Area.¹⁴
In New York City, any work that alters, rearranges, relocates or permanently removes piping must be supervised by a Licensed Master Plumber, who obtains the permits from DOB and arranges the tests and inspections.¹⁵

Checked October 12, 2026

Before you hire

New York has no statewide contractor license, so check the city or county home improvement license where one is required, and make sure any job over $500²⁷ comes with the written contract state law calls for.

How to check a contractor's license in New York

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Cellar or basement

Under the Multiple Dwelling Law, a cellar is an enclosed space with more than half of its height below the curb level, and it does not count as a story.¹¹ A basement, by the same law, is a story partly below the curb level but with at least half of its height above it.¹² Measure from the curb in front of the house, not from the backyard, before deciding what the room can become.

Under the state Multiple Dwelling Law, residential use is prohibited in cellars but allowed in basements, so whether a lower level counts as a cellar or a basement decides whether anyone may live in it.³ That leaves a finished cellar for uses other than living space, and the city's ADU rules set a separate bar before any lower level can become an apartment. DOB's ADU rules require at least 7 feet of ceiling height in every habitable room, and a cellar's ceiling must be at least 2 feet above grade.¹³

Flooding and sewer backups

Basement and cellar ADUs are not permitted in the city's high-risk flood areas: FEMA's Special Flood Hazard Area, the Coastal Flood Risk Area and DEP's 10-Year Rainfall Flood Risk Area.¹⁴ Even for a family room, a lot inside one of those areas is a reason to choose water-tolerant finishes and to keep outlets and equipment as high as the plan allows.

DEP's homeowner guide says a backwater valve can keep sewer water from backing up into a home through basement plumbing fixtures, that basement fixtures shouldn't be used while the valve is closed, and that a plumber can help decide whether one makes sense for the house.⁶ In New York City, property owners own and must maintain and repair the sewer service line that connects the property to the city sewer in the street.¹⁶ A backwater valve goes into that line, which makes it piping work for a Licensed Master Plumber. In New York City, any work that alters, rearranges, relocates or permanently removes piping must be supervised by a Licensed Master Plumber, who obtains the permits from DOB and arranges the tests and inspections.¹⁵

DOB is the city's floodplain administrator, and an existing building in the floodplain that undergoes a substantial improvement, or was substantially damaged, must be brought fully up to the flood-zone rules as if newly built, which for a home includes raising living space and filling basements or cellars to grade.¹⁷

Radon runs low here, but test anyway

The New York State Department of Health's list of high radon area counties names 40 counties, and none of the five New York City counties is among them; the department still recommends testing all homes.¹⁸ The EPA recommends testing for radon on the lowest lived-in level, so a basement that hasn't been tested should be tested before it is remodeled; fixing a radon problem is usually easier and cheaper before the basement is finished.¹⁹

To use a basement or cellar apartment as an ADU, qualified professionals must test its radon and soil vapor levels and certify to the Department of Buildings that the results are below the levels the NYC Health Department sets.²⁰ The EPA's guidance is to fix your home if radon tests at 4 picocuries per liter or higher, and to consider fixing it between 2 and 4.²¹

Keeping the space dry

Before turning basement space into living space, the EPA advises checking it for leaks and other signs of moisture and fixing any moisture problem first, because damp basements promote mold and other biological growth.¹⁹ The EPA warns that carpet on a basement slab can stay damp from water or vapor coming up through the concrete, or from room moisture condensing on a slab that is colder than the air, and either can lead to mold.¹⁹

For the inside of basement walls, Building America calls for rigid foam fully adhered to the foundation with sealed seams, or spray foam, and rates closed-cell spray foam as the best moisture control of the interior options.⁹ Because finishing a basement changes how air moves through a house, the EPA advises having a professional check afterward that new and existing combustion equipment is not backdrafting.¹⁹ In a city house where the boiler and water heater share the basement, that check matters once the space is closed in.

If the plan is a basement apartment

In December 2024, alongside the City of Yes for Housing Opportunity zoning change, New York City enacted Local Laws 126 and 127, letting the owner of a one- or two-family home add an ancillary dwelling unit in an attic, basement or cellar, in a free-standing building or in an attached addition.¹⁴ Every habitable room in an ADU must meet the emergency escape and rescue opening requirements of the city's Building and Fire Codes.¹³ Sprinklers are required in most ADUs; the exception is an above-grade ADU within a one-family home, and attic ADUs must always be sprinklered.¹³

The Local Law 126 pilot for legalizing existing basement and cellar apartments covers only Bronx Community Districts 9 through 12, Brooklyn Community Districts 4, 10, 11 and 17, Manhattan Community Districts 2, 3 and 9 through 12, and Queens Community District 2.¹⁴ To enter the legalization pilot, a basement or cellar unit must have existed before April 20, 2024 and the owner must apply before April 20, 2029; enrolled units then follow a ten-year compliance schedule, and DOB is not taking applications until its program rules are issued.¹⁴

The cellar stairs, later on

More than one in four adults 65 and older fall each year.²² The steep, narrow stairs down to many city basements are a likely place for one. While the space is being finished, add a second handrail, a light switch at the top and the bottom, and treads in a color that contrasts with the floor. NAHB's Certified Aging-in-Place Specialist (CAPS) credential trains remodelers in home modifications for aging in place.²³

What happens when you call

When you call the number on this page, a recorded line connects you with one independent company that handles basement finishing in the New York City area. What gets built, when and for how much is between you and that company.

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After you're connected

Look the company up with DCWP before any deposit changes hands. New York City requires a Department of Consumer and Worker Protection Home Improvement Contractor license for residential construction, repair or remodeling work that costs more than $200; new construction, plumbing and purely electrical work are not covered.²⁴ DCWP's online Search Business tool shows whether a business or individual holds a DCWP license, without logging in, and can be searched by name or DCWP license number.²⁵ Check a New York license

Ask who will file the DOB plans and the plumbing and electrical permits, and whose license goes on each. In New York City, the Department of Buildings licenses master plumbers and master electricians, and its License Search confirms a license's status and any disciplinary actions.²⁶

Questions people ask

What does it cost to finish a basement in New York City?

In the 2025 Cost vs. Value report the New York market's basement job came to $61,417¹, with $35,572¹ of that expected back when the home sells. A backwater valve, flood-resistant finishes and any new escape window are priced separately.

Can I put a bedroom in my cellar?

Not as living space. Under the state Multiple Dwelling Law, residential use is prohibited in cellars but allowed in basements, so whether a lower level counts as a cellar or a basement decides whether anyone may live in it.³

Do I need to test for radon in New York City?

None of the boroughs is on the state's high-radon list, but testing before you finish is still the advice. The EPA recommends testing for radon on the lowest lived-in level, so a basement that hasn't been tested should be tested before it is remodeled; fixing a radon problem is usually easier and cheaper before the basement is finished.¹⁹

Can I rent out my basement as an apartment?

Possibly, under the city's ADU rules, if your lot is outside the high-risk flood areas. Basement and cellar ADUs are not permitted in the city's high-risk flood areas: FEMA's Special Flood Hazard Area, the Coastal Flood Risk Area and DEP's 10-Year Rainfall Flood Risk Area.¹⁴ When the ADU is first occupied, the property must be the primary residence of one of its owners.¹⁴

Sources

Page updated October 12, 2026. How we source our numbers

Zonda / Journal of Light Construction, Cost vs. Value 2025, New York, NY. Released 2025. New York, NY (Cost vs. Value market). Industry source.
Zonda / Journal of Light Construction, Cost vs. Value 2025, national. Released 2025. United States. Industry source.
Office of the New York City Comptroller, Bringing Basement Apartments Into the Light. Released August 30, 2022. New York City.
Zonda / Journal of Light Construction, Cost vs. Value project description: Basement Remodel. Released September 18, 2025. View source. Industry source.
NOAA National Centers for Environmental Information, U.S. Climate Normals 1991–2020. Released 2021. Central Park, Manhattan (station USW00094728), LaGuardia Airport, Queens (station USW00014732).
NYC Department of Environmental Protection, Rainfall Ready NYC: A Homeowner's Guide. Released July 2022. View source.
U.S. Census Bureau, American Community Survey 2020–2024 5-year, table B25024. Released January 29, 2026. New York City, NY, Queens County, NY.
U.S. Census Bureau, American Community Survey 2020–2024 5-year, table B25034. Released January 29, 2026. New York City, NY, Queens County, NY.
U.S. Department of Energy, Building America Top Innovations: Basement Insulation Systems. No publication date. View source.
NYC Department of Buildings, Obtaining a Permit. No publication date. View source.
New York State Senate, Multiple Dwelling Law § 4 (definitions), subdivision 37. No publication date. View source.
New York State Senate, Multiple Dwelling Law § 4 (definitions), subdivision 38. No publication date. View source.
NYC Department of Buildings, Ancillary Dwelling Units FAQs. No publication date. View source.
NYC Department of Buildings, Ancillary Dwelling Units (Local Laws 126/127). Released April 9, 2026. View source.
NYC Department of Buildings, Plumbing Permits. No publication date. View source.
NYC Department of Environmental Protection, Sewer Backup. No publication date. View source.
NYC Housing Recovery Office, Resources: Department of Buildings. No publication date. View source.
New York State Department of Health, Protect Your Family From Radon: A Guide for New York State Residents (publication 3168). No publication date. View source.
U.S. Environmental Protection Agency, Remodeling Your Home and Indoor Air Quality. Released February 17, 2026. View source.
NYC Department of Health and Mental Hygiene, Indoor Air Quality: Testing for Radon and Soil Vapor in ADUs. No publication date. View source.
U.S. Environmental Protection Agency, Health Risk of Radon. Released June 24, 2026. View source.
Centers for Disease Control and Prevention, Facts About Older Adult Falls. Released September 4, 2026. View source.
National Association of Home Builders, Certified Aging-in-Place Specialist (CAPS). No publication date. View source. Industry source.
NYC Department of Consumer and Worker Protection, Wall of Shame: Unlicensed Home Improvement Contractors. Released October 1, 2026. View source.
NYC Department of Consumer and Worker Protection, Check a License. No publication date. View source.
NYC Department of Buildings, Know Your Construction Professional. No publication date. View source.
New York State Senate (Open Legislation), General Business Law, Article 36-A, Section 770. Released May 29, 2020. New York State.