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Cortlandt · ADU cost

What it costs to build an ADU in Cortlandt, NY

800 sq ft ≈ $235k–310k $296–388/sq ft 21 districts Con Edison

An 800 sq ft accessory dwelling unit in Cortlandt runs roughly $235k–310k, or about $296–388/sq ft, and that per-square-foot figure sits deliberately above the $242–318/sq ft a full house costs here. An ADU still needs one whole kitchen, one whole bath, its own service panel and its own heating plant no matter how small you draw it, and those costs do not shrink with the floor plan, so they land on half the square footage and push the rate up. Whether the town will let you build one is a separate question from what it costs, and it gets answered parcel by parcel rather than townwide, since the Town of Cortlandt maps 21 districts that treat accessory units differently from one another, so read the table below as a starting point rather than a verdict.

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ADU cost by size in Cortlandt

Standard finish, slab on grade, on a flat and clear part of the lot, general-contractor margin included. These are structure costs at Westchester County pricing, before the service and septic work a second dwelling can trigger.

SizeType$ / sq ftEstimated total
400 sq ft Studio $392–$514 $155k–205k
600 sq ft One bedroom $328–$430 $195k–260k
800 sq ft One bedroom, larger $296–$388 $235k–310k
1,000 sq ft Two bedroom $277–$362 $275k–360k

400 sq ft — One room plus a bath. Garage conversions and small backyard cottages land here.

600 sq ft — The most common detached build - a real bedroom, full kitchen, one bath.

800 sq ft — Room for a proper living area. Still a single bath and one kitchen.

1,000 sq ft — About as large as most codes allow an accessory unit to go.

Why the rate is higher than a house

The systems below are priced for an 800 sq ft unit. The middle column is what each system would cost if it simply shrank with the floor plan; the left column is what it actually costs once you account for the equipment a dwelling needs one of regardless of size. The gap between the two columns is the whole reason small builds price the way they do.

System$ / sq ft in an ADUIf it scaled with floor areaFixed per unit
Site work $9–$13 $9 —
Foundation $19–$27 $19 —
Framing $30–$38 $30 —
Envelope - roof, siding, windows $38–$49 $38 —
Plumbing $33–$40 $19 55%
Electrical $22–$28 $15 35%
HVAC $27–$34 $17 45%
Insulation $9–$11 $9 —
Interior finishes $38–$51 $32 15%
Millwork & cabinetry $22–$33 $13 55%

The fixed-per-unit share is a modeling assumption, not a figure from the code: it is our estimate of how much of each system's budget buys equipment a dwelling needs exactly one of - a kitchen rough-in, a bath group, a service panel, a heating plant - and therefore does not shrink when the unit does. Site work, foundation, framing, envelope and insulation are treated as scaling straight with floor area, which understates the premium slightly, because a small building carries more envelope per square foot of floor than a large one.

What the Cortlandt code says about accessory units

Whether you can build one, and how large, is decided by the district your parcel sits in rather than by the town as a whole. The table shows how each mapped district treats ADUs alongside the lot and setback standards a second unit still has to fit inside. District boundaries and conditions vary, so treat it as a starting point and confirm the district that applies to your parcel.

District Min lot Setbacks F / S / R Max height ADU
Single-Family Residential District — — — Occupancy restricted
Single-Family Residential District 1.84 ac 50 / 30 / 30 ft 35 ft Occupancy restricted
Single-Family Residential District 0.92 ac 50 / 30 / 30 ft 35 ft Occupancy restricted
Single-Family and Two-Family Residential District 0.92 ac 50 / 30 / 30 ft 35 ft Occupancy restricted
Single-Family Residential District 0.23 ac 25 / 6 / 20 ft 35 ft Occupancy restricted
Single-Family Residential District 0.34 ac 30 / 10 / 25 ft 35 ft Occupancy restricted
Single-Family Residential District 0.46 ac 35 / 15 / 30 ft 35 ft Occupancy restricted
General Residential District 0.17 ac 25 / 6 / 20 ft 40 ft Occupancy restricted
Planned Village Development — — — —
Designed Industrial District 5 ac 75 / 75 / 75 ft 40 ft No
Community Commercial District 0.34 ac 30 / 10 / 10 ft 35 ft Occupancy restricted
Designed Commercial District 1.84 ac 75 / 50 / 50 ft 35 ft No
Conditional M-1 — — — —
Highway Commercial District 0.46 ac 30 / 30 / 30 ft 35 ft Occupancy restricted
HC-9A District 0.46 ac 30 / 30 / 30 ft 35 ft Occupancy restricted
Light Industrial District 0.46 ac 40 / 20 / 30 ft 40 ft No
Camp Smith Reuse District B — — 40 ft —
Conservation, Recreation and Open Space District 15 ac 50 / 50 / 30 ft 35 ft Occupancy restricted
Parks, Recreation and Open Space District — — — No
Annsville Waterfront Enhancement District 0.17 ac 10 / 10 / 10 ft 35 ft —
M-1A District — — — —

Single-Family Residential District - Chapter 307 publishes no dimensional figures for R-160.

  • A two-family home in a transitional location needs a special permit and takes the R-G two-family standards: at least 10,000 sq ft, 70 ft of width and at most 45 percent building coverage (§ 307-48).
  • The front yard may be reduced to the average of the improved lots where at least half the lots on the same side of the street within 500 feet already hold single or two-family homes (§ 307-18A).
  • On a corner lot every yard facing a street counts as a front yard for the main building (§ 307-18G).
  • A building owned and occupied by a government agency or a public school may reach 75 feet if every yard is widened one foot for each extra foot of height (§ 307-18F).
  • The Town Board may authorize a cluster subdivision, which may hold no more homes than a conventional layout would (§ 307-19).

Single-Family Residential District, Single-Family Residential District, Single-Family Residential District - A two-family dwelling is a special permit use, and only in a transitional location; it then takes the R-G two-family standards: at least 70 ft of width, 25 ft of front yard, 6 ft on one side and 20 ft of rear yard, up to 40 ft of height and 45 percent building coverage.

  • A transitional location is a lot whose side line runs along a commercial or industrial district for at least half its length, or whose front line faces one across the street for over half of it.
  • The front yard may be reduced to the average of the improved lots where at least half the lots on the same side of the street within 500 feet already hold single or two-family homes (§ 307-18A).
  • A Town Board cluster subdivision may hold no more homes than a conventional layout would, and its setback from the boundary of the tract is the district's own figure for one-family homes (§ 307-19).
  • On a corner lot every yard facing a street counts as a front yard for the main building (§ 307-18G).
  • An accessory building may not stand in a front yard, is limited to 17 feet in height and needs 6 feet to the side and rear lines; one holding an accessory dwelling unit owes the main building's yards.
  • A flag lot needs at least 50 feet of frontage, and the access strip does not count toward lot area (§ 307-18I).

Single-Family and Two-Family Residential District - An existing lot in two-family use needs at least 20,000 square feet and 100 feet of width and 15 feet of side yard, and may cover 30 percent of the lot; a new lot laid out for a two-family home meets the standard lot figures.

  • The front yard, the rear yard and the height are the same either way.
  • A two-family dwelling in a transitional location is a separate special permit route under § 307-48 and takes the R-G two-family standards.
  • The front yard may be reduced to the average of the improved lots where at least half the lots on the same side of the street within 500 feet already hold single or two-family homes (§ 307-18A).
  • On a corner lot every yard facing a street counts as a front yard for the main building (§ 307-18G).
  • An accessory building may not stand in a front yard, is limited to 17 feet in height and needs 6 feet to the side and rear lines; one holding an accessory dwelling unit owes the main building's yards.
  • All accessory structures together may not cover more than the main building's footprint, and no single one may exceed 70 percent of it.

Single-Family Residential District, Single-Family Residential District - A two-family dwelling is a special permit use, and only in a transitional location; it then takes the R-G two-family standards: at least 70 ft of width, 25 ft of front yard, 6 ft on one side and 20 ft of rear yard, up to 40 ft of height and 45 percent building coverage.

  • A transitional location is a lot whose side line runs along a commercial or industrial district for at least half its length, or whose front line faces one across the street for over half of it.
  • The front yard may be reduced to the average of the improved lots where at least half the lots on the same side of the street within 500 feet already hold single or two-family homes (§ 307-18A).
  • A Town Board cluster subdivision may hold no more homes than a conventional layout would, and its setback from the boundary of the tract is the district's own figure for one-family homes (§ 307-19).
  • On a corner lot every yard facing a street counts as a front yard for the main building (§ 307-18G).
  • An accessory building may not stand in a front yard, may not be over 17 ft tall, and needs 6 ft to the side line and 10 ft to the rear; one holding an accessory dwelling unit owes the house's yards.
  • A flag lot needs at least 50 feet of frontage, and the access strip does not count toward lot area (§ 307-18I).

General Residential District - A two-family dwelling needs at least 10,000 square feet of lot and 70 feet of width and may cover 45 percent of the lot; the yards and the height are the same either way.

  • A two-family dwelling built or converted before November 9, 1993 is permitted outright; a new one needs a special permit (§ 307-64).
  • There is no 12-foot limit on the height of a single story here.
  • The front yard may be reduced to the average of the improved lots where at least half the lots on the same side of the street within 500 feet already hold single or two-family homes (§ 307-18A).
  • On a corner lot every yard facing a street counts as a front yard for the main building (§ 307-18G).
  • An accessory building may not stand in a front yard, is limited to 17 feet in height and needs 6 feet to the side and rear lines; one holding an accessory dwelling unit owes the main building's yards.
  • All accessory structures together may not cover more than the main building's footprint, and no single one may exceed 70 percent of it.

Planned Village Development - The lot and yard standards for PVD are not confirmed. Confirm them with the Town of Cortlandt Department of Technical Services before planning a building.

Designed Industrial District - At least 40 percent of the lot area must be landscaped, which is a minimum planting requirement and not a cap on paving, and the landscaping separating buildings, parking and driveways from the street must be a continuous strip 25 feet wide (§ 307-21B(2)).

  • The height limit is stated as 3 stories or 40 feet, whichever is less.
  • A contractor's yard or a specialty trade contractor is a special permit use whose own standards cap impervious coverage, including the buildings, at 55 percent of the site (§§ 307-65.5 and 307-65.6).
  • Outdoor light fixtures may not be mounted higher than 20 feet above average finished grade (§ 307-12.3).
  • On a corner lot every yard facing a street counts as a front yard for the main building (§ 307-18G).
  • An existing building with more than 20,000 square feet per floor is not treated as dimensionally nonconforming.

Community Commercial District - On a lot connected to a public sewer the minimum is 7,500 square feet of lot and 60 feet of width, with 5,000 square feet of land for each dwelling unit; the yards, the height and the coverage are the same either way.

  • A building is capped at 12,000 square feet of floor area, or 75,000 square feet for a self-storage facility, and no single use other than a food store may occupy more than 4,000 square feet.
  • At least 30 percent of the lot area must be landscaped, which is a minimum planting requirement and not a cap on paving.
  • The height limit is stated as 2 1/2 stories or 35 feet, whichever is less.
  • An active adult residential community needs a Planning Board special permit and at least eight acres, and is capped at 17 units per acre, 50 feet, three stories and 135,000 sq ft of floor area.
  • A self-storage facility needs a Planning Board special permit, is limited to lots fronting Route 202 or Route 35, and takes the larger of the district figure or 40,000 sq ft of lot (§ 307-65.11).
  • The Town Board may authorize a cluster subdivision in a CC district as well as in the residential districts (§ 307-19B(2)).

Designed Commercial District - A multifamily dwelling is allowed without a special permit only on a parcel that is also inside the Downtown Neighborhood Overlay, and there the overlay replaces the district's bulk standards for any building containing multifamily units (§ 307-96.4).

  • Inside that overlay such a building needs 20,000 square feet of lot, 80 feet of width and 1,800 square feet of land per unit, and may reach 47 feet and four stories with 50 percent building coverage.
  • The overlay also sets a maximum rather than a minimum front yard for such a building.
  • At least 25 percent of the lot must be landscaped, a minimum planting requirement and not a cap on paving, and the landscaping along the street must be a continuous strip 25 feet wide (§ 307-21B(2)).
  • The height limit is stated as 3 stories or 35 feet, whichever is less.
  • A self-storage facility needs a Planning Board special permit, is limited to lots fronting Route 202 or Route 35, and takes the larger of the district figure or 40,000 sq ft of lot (§ 307-65.11).
  • On a corner lot every yard facing a street counts as a front yard for the main building (§ 307-18G).

Conditional M-1 - The standards that govern COND M-1 parcels are not confirmed. Confirm them with the Town of Cortlandt Department of Technical Services before planning a building.

Highway Commercial District - A multifamily development needs a site of at least five acres and no more than 15 acres, and is allowed without a special permit only on a parcel that is also inside the Downtown Neighborhood Overlay (§ 307-65B(1)).

  • It must be on municipal sewer or an approved disposal system and on a public or approved water supply.
  • Inside that overlay such a building needs 20,000 square feet of lot, 80 feet of width and 1,800 square feet of land per unit, and may reach 47 feet and four stories with 50 percent building coverage.
  • The overlay also sets a maximum rather than a minimum front yard for such a building.
  • At least 30 percent of the lot must be landscaped, a minimum planting requirement and not a cap on paving, and the landscaping along the street must be a continuous strip 25 feet wide (§ 307-21B(2)).
  • The height limit is stated as 2 1/2 stories or 35 feet, whichever is less.
  • A self-storage facility needs a Planning Board special permit, is limited to lots fronting Route 202 or Route 35, and takes the larger of the district figure or 40,000 sq ft of lot (§ 307-65.11).

HC-9A District - The yards shown are for commercial use; a residential-only use owes 30 ft front, 10 ft side and 25 ft rear, and a mixed-use building owes 30 ft front, 25 ft side and 25 ft rear.

  • A residential-only or mixed-use building needs 7,500 square feet of land for each dwelling unit and must keep 25 percent of the lot landscaped rather than 30 percent.
  • That landscaping figure is a minimum planting requirement and not a cap on paving.
  • Three and four-unit dwellings are limited to two bedrooms per unit.
  • Single-family, two-family and three to four-family dwellings are permitted here, and a multifamily dwelling needs a special permit.
  • The height limit is stated as 2 1/2 stories or 35 feet, whichever is less.
  • On a corner lot every yard facing a street counts as a front yard for the main building (§ 307-18G).

Light Industrial District - The landscaping separating buildings, parking and driveways from the street must be a continuous strip 25 feet wide (§ 307-21B(2)), and the height limit is given in feet alone, with no story limit.

  • A contractor's yard or a specialty trade contractor is a special permit use whose own standards cap impervious coverage, including the buildings, at 55 percent of the site (§§ 307-65.5 and 307-65.6).
  • On a corner lot every yard facing a street counts as a front yard for the main building (§ 307-18G).
  • An existing building with more than 20,000 square feet per floor is not treated as dimensionally nonconforming.

Camp Smith Reuse District B - The 5,000 square feet is land area for each dwelling unit rather than a minimum lot size, and the Town Board may reduce it by as much as 1,000 square feet on a lot where other land is preserved as open space by deed restriction (§ 307-95E(4)(a)).

  • The code publishes no lot minimum, no lot width and no yard standards for the district.
  • At least 25 percent of the lot must be kept as landscape coverage, which is a minimum planting requirement and not a cap on paving.
  • Parks and recreation are the only uses of right; homes, retail, offices, lodging, institutional uses and manufacturing are all reachable only by Town Board special permit (§ 307-95B).
  • The land uses must be mixed so that the residential area does not exceed the commercial and open space area.
  • The maximum height may be modified by a local law providing for incentive zoning.

Conservation, Recreation and Open Space District - The district is not applied to an area of less than 25 acres unless the parcel is already encumbered by a conservation easement, a use restriction or a cluster subdivision set-aside (§ 307-12.2C).

  • An accessory building may not stand in a front yard, is limited to 17 feet in height and needs 6 feet to the side and rear lines; one holding an accessory dwelling unit owes the main building's yards.
  • All accessory structures together may not cover more than the main building's footprint, and no single one may exceed 70 percent of it.
  • Each story may not exceed 12 feet.
  • On a corner lot every yard facing a street counts as a front yard for the main building (§ 307-18G).
  • A building owned and occupied by a government agency or a public school may reach 75 feet if every yard is widened one foot for each extra foot of height (§ 307-18F).

Parks, Recreation and Open Space District - Chapter 307 publishes no dimensional figures for PROS.

  • The general rules of § 307-18 still apply, including that on a corner lot every yard facing a street counts as a front yard for the main building.

Annsville Waterfront Enhancement District - Multifamily development is allowed outright only in the AWE-4 subarea and mixed-use only in the AWE-2, AWE-3 and AWE-4 subareas, at no more than five units per acre; the yards may be increased by the district's design guidelines.

  • The bonuses are 70 feet of height in AWE-1, 15 units per acre with four stories or 50 feet in AWE-2, and 15 units per acre in AWE-3.
  • In AWE-4 the bonus is 20 units per acre, or 40 units per acre with five stories or 55 feet where the project dedicates a publicly accessible waterfront walkway.
  • A bonus is earned with an amenity package that must include infrastructure investment or a cash payment to the Town, and it needs municipal water and sewer on or reasonably adjacent to the site.
  • Any multifamily unit is capped at 1,200 square feet, and a building with more than five units must set aside at least 10 percent of them as affordable under the Westchester County definition.
  • An active adult residential community needs a Planning Board special permit and at least eight acres, and is capped at 17 units per acre, 50 feet, three stories and 135,000 sq ft of floor area.
  • Multifamily in AWE-4 must include ground-floor commercial space at the Sprout Brook Road and Dogwood Road intersections on Albany Post Road.

M-1A District - Chapter 307 publishes no dimensional figures for M-1A.

  • The district takes the same permitted uses as the Light Industrial district and adds the composting of organic waste (§ 307-96).
  • Rock crushing is a special permit use that may be carried on only in this district (§ 307-65.9).
  • Outdoor light fixtures may not be mounted higher than 20 feet above average finished grade (§ 307-12.3).
  • On a corner lot every yard facing a street counts as a front yard for the main building (§ 307-18G).
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Size limits on record in Cortlandt

Where the code states a size cap, it decides which row of the cost table above actually applies to you. These are the caps recorded for Cortlandt:

Costs an ADU adds that a house does not

Sizing up a specific parcel in Cortlandt?

Aldo pulls the exact zoning district, setbacks, and build feasibility for any parcel — before you buy. Enter your email to open Aldo and run your free report.

Building a full house instead?

A standard-finish house in Cortlandt runs $242–318/sq ft, about $435k–570k at 1,800 sq ft , plus roughly $7,657 for a conforming lot. See what it costs to build a house in Cortlandt.

ADU cost in nearby towns

Mount Vernon (City)
800 sq ft ≈ $235k–310k
New Rochelle (City)
800 sq ft ≈ $235k–310k
Peekskill (City)
800 sq ft ≈ $235k–310k
Rye (City)
800 sq ft ≈ $235k–310k
White Plains (City)
800 sq ft ≈ $235k–310k
Yonkers (City)
800 sq ft ≈ $235k–310k

All Westchester County towns: Mount Vernon (City) · New Rochelle (City) · Peekskill (City) · Rye (City) · White Plains (City) · Yonkers (City) · Bedford · Eastchester · Greenburgh · Lewisboro · Mamaroneck · Mount Pleasant · New Castle · North Castle · North Salem · Ossining · Pound Ridge · Somers · Yorktown · Harrison (Village) · Ardsley (Village) · Briarcliff Manor (Village) · Bronxville (Village) · Buchanan (Village) · Croton-on-Hudson (Village) · Dobbs Ferry (Village) · Elmsford (Village) · Hastings-on-Hudson (Village) · Irvington (Village) · Larchmont (Village) · Mamaroneck (Village) · Mount Kisco (Village) · Ossining (Village) · Pelham (Village) · Pelham Manor (Village) · Pleasantville (Village) · Port Chester (Village) · Rye Brook (Village) · Scarsdale (Village) · Sleepy Hollow (Village) · Tarrytown (Village) · Tuckahoe (Village)

More on Cortlandt: Can you build an ADU here? · Zoning for new construction · Westchester County build cost

ADU cost in Cortlandt: common questions

How much does it cost to build an ADU in Cortlandt, NY?

An 800 sq ft accessory dwelling unit in Town of Cortlandt runs roughly $235k–310k at a standard finish, general-contractor margin included. A 400 sq ft studio runs about $155k–205k. Those are structure costs on an easy site and do not include the septic, water or electrical service work a second unit often triggers.

Why does an ADU cost more per square foot than a house in Cortlandt?

Because a lot of a dwelling's cost is per dwelling, not per square foot. One kitchen, one bath group, one service panel and one heating plant cost about the same in an 800 sq ft cottage as in a 1,800 sq ft house, so on the smaller unit they get spread over less than half the floor area. That is why an ADU here prices at $296–388/sq ft against $242–318/sq ft for a full house, even though it is the same trades doing the same work.

Are ADUs allowed in Cortlandt?

Town of Cortlandt has 21 districts. 12 districts allow ADUs with occupancy restrictions, 4 do not. 5 districts have incomplete data - verify with the building department at (914) 734-1010. Check the specific address with the free ADU checker before you spend money on design.

Can I rent an ADU in Cortlandt short term?

Short-term rentals allowed with local rules for Town of Cortlandt. ADU rules and short-term-rental rules are set separately, so a unit you are allowed to build is not automatically one you are allowed to rent nightly. Confirm both before you underwrite the build on short-term-rental income.

ADU costs are modeled estimates in current 2026 dollars at the Westchester County regional index, general-contractor margin included, derived from Offsite's cost engine with a stated adjustment for the equipment a dwelling needs one of regardless of size. They are planning numbers for decision-support only - not a bid, quote, or guarantee, and not legal, architectural or engineering advice. They cover the structure and exclude septic expansion, utility service runs, site work beyond a flat and clear pad, and permit fees. ADU eligibility, size, owner-occupancy and permit conditions in the Town of Cortlandt vary by district and often carry exceptions this page does not show; zoning last reviewed 2026-09-26; verify with the building department at (914) 734-1010 before relying on any answer. Sources: the Offsite / Aldo cost engine and zoning dataset.

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