White Plains · ADU cost
What it costs to build an ADU in White Plains, NY
An 800 sq ft accessory dwelling unit in White Plains 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 city 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 City of White Plains maps 33 districts that treat accessory units differently from one another, so read the table below as a starting point rather than a verdict.
ADU cost by size in White Plains
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.
| Size | Type | $ / sq ft | Estimated 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 ADU | If it scaled with floor area | Fixed 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 White Plains 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 |
|---|---|---|---|---|
| Residential One Family | 0.4591 ac | — | 30 ft | Occupancy restricted |
| Residential One Family | 0.6887 ac | — | 30 ft | Occupancy restricted |
| Residential One Family | 0.287 ac | — | 30 ft | Occupancy restricted |
| Residential One Family | 0.1722 ac | — | 30 ft | Occupancy restricted |
| Residential One Family | 0.1148 ac | — | 30 ft | No |
| Residential One and Two Family | 0.1148 ac | — | 30 ft | No |
| Residential One and Two Family | — | — | — | No |
| Residential Multi-Family | 0.1148 ac | — | 35 ft | No |
| Residential Multi-Family | 0.1148 ac | — | 35 ft | No |
| Residential Multi-Family | 0.1148 ac | — | 35 ft | No |
| Residential Townhouse | 0.1148 ac | — | 35 ft | No |
| Residential Townhouse | 0.1148 ac | — | 35 ft | No |
| Residential Multi-Family | 0.4591 ac | — | 35 ft | No |
| Residential Multi-Family | 0.1148 ac | — | 35 ft | No |
| Residential Multi-Family | 0.1148 ac | — | 35 ft | No |
| Residential Multi-Family | 0.2296 ac | — | 125 ft | No |
| Residential Multi-Family | 0.3444 ac | — | 125 ft | No |
| Residential Multi-Family | — | — | 35 ft | No |
| Campus Office | 10 ac | — | 50 ft | No |
| Restricted Business | — | — | 50 ft | No |
| Neighborhood Business | — | — | 25 ft | No |
| Intermediate Business | — | — | 50 ft | No |
| Enclosed Mall | — | — | 90 ft | No |
| Business Residential -1 | — | — | 35 ft | No |
| Business Residential -2 | — | — | 65 ft | No |
| Core Business-1 | — | — | — | No |
| Core Business-2 | — | — | — | No |
| Core Business-3 | — | — | — | No |
| Core Business-4 | — | — | — | No |
| Office-Residential | — | — | 40 ft | No |
| Urban Renewal Central Business | — | — | 230 ft | No |
| Light Industrial | 0.1148 ac | — | 50 ft | No |
| Planned Senior Residential Development District | 0.0689 ac | — | — | — |
Costs an ADU adds that a house does not
- Septic and water A second dwelling adds bedrooms to the design flow, which on an unsewered parcel often means expanding or replacing the existing system rather than tapping it. This is the single most common reason an ADU budget moves after design, and it is site-specific enough that no model should quote it - get it evaluated early.
- Utility service Con Edison territory. A detached unit needs power run to it, and whether it goes on its own meter or subfeeds the main house changes both the cost and the permit path.
- Access and parking Many codes require an added parking space for the accessory unit, and a detached unit usually needs a driveway extension or a path, both of which count against a lot-coverage or impervious-surface cap.
- Short-term rentalsNo local short-term-rental law on record - which is not the same as permission. The earlier note attributed a short-term-rental registration and licensing requirement to 'Chapter 9-7 of the City Code'; Chapter 9-7 is Affordable Housing Regulations. The Rental Housing Registry and License Program is an ordinance of the Common Council of 18 June 2018 adding §§ 4-28-1 et seq. to Title IV, Article I of the White Plains Municipal Code — and it never mentions short-term rentals, transient occupancy or any rental period. Both documents were read in full 2026-08-27, together with the City Zoning Ordinance as amended through 5 February 2024 (296 pp.), which returns zero hits for 'short-term'. WHAT ACTUALLY GOVERNS IS THE ZONING ORDINANCE'S CLOSED USE SCHEDULE. Section 5 states: 'Any use not specifically listed as being permitted shall be deemed to be prohibited.' No residential district in the Schedule of Use Regulations lists any transient-lodging use. The only lodging-adjacent entry in a residential district is a Permitted Accessory Use — 'the keeping of not more than two roomers per dwelling unit' in the R1 districts, and not more than one roomer per dwelling unit in a one- or two-family dwelling in the R2 and RM districts. A 'roomer' is defined as the occupant of a 'rooming unit', and a 'rooming house' (a dwelling containing three or more rooming units) is a special permit use in only some districts. 'Hotel' is defined by rooms 'occupied by transient guests who are lodged ... which rooms have primary access from interior lobbies' — a commercial building, not a house. TOURIST HOMES GET ONE MENTION AND IT IS A NEGATIVE: the definition of 'customary home occupation' states that tea rooms, barber shops, beauty parlors, real estate and insurance offices, limousine and taxi operations 'and tourist homes are not customary home occupations.' THE REGISTRY IS STILL A REAL OBLIGATION FOR AN UNHOSTED LET. § 4-28-4: 'It shall be unlawful ... to conduct, keep, manage, or operate ... any rental housing unit until a Rental Housing License is issued by the Department of Building.' A 'rental housing unit' is any dwelling unit being rented or intended to be rented. § 4-28-3 EXEMPTS owner-occupied single-family dwellings, two-family dwellings where one unit is owner-occupied, condominium and co-operative buildings, multifamily buildings of more than twelve units, hotels/motels/rooming houses/group homes/nursing homes and assisted living, and government-managed multifamily. So a non-owner-occupied White Plains house let out is inside the registry; an owner-occupied one is not. Licences run 1 January to 31 December and require landlord inspections reported to the City. The registry licenses rental housing generally — it does not authorise a transient use that the zoning schedule does not list. Get the Department of Building's written position before underwriting nightly income: (914) 422-1269. Separate question from whether you can build the unit.
- Building dept(914) 422-1269
Sizing up a specific parcel in White Plains?
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 White Plains runs $242–318/sq ft, about $435k–570k at 1,800 sq ft , plus roughly $539 for a conforming lot. See what it costs to build a house in White Plains.
ADU cost in nearby towns
All Westchester County towns: Harrison (City) · Mount Vernon (City) · New Rochelle (City) · Peekskill (City) · Rye (City) · Yonkers (City) · Bedford · Cortlandt · Eastchester · Greenburgh · Lewisboro · Mamaroneck · Mount Pleasant · New Castle · North Castle · North Salem · Ossining · Pound Ridge · Somers · Yorktown · 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 White Plains: Can you build an ADU here? · Zoning for new construction · Westchester County build cost
ADU cost in White Plains: common questions
How much does it cost to build an ADU in White Plains, NY?
An 800 sq ft accessory dwelling unit in City of White Plains 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 White Plains?
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 White Plains?
City of White Plains has 33 districts. 28 districts prohibit ADUs, 4 allow them with occupancy restrictions. 1 district has incomplete data - verify with the building department at (914) 422-1269. Check the specific address with the free ADU checker before you spend money on design.
Can I rent an ADU in White Plains short term?
No local short-term-rental law on record - which is not the same as permission for City of White Plains. 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 City of White Plains vary by district and often carry exceptions this page does not show; zoning last reviewed 2026-06-08; verify with the building department at (914) 422-1269 before relying on any answer. Sources: Offsite / Aldo cost engine (costEngine.js + constants.js); zoning dataset (municipalData.js).