Mount Pleasant · ADU cost
What it costs to build an ADU in Mount Pleasant, NY
An 800 sq ft accessory dwelling unit in Mount Pleasant 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 Mount Pleasant maps 32 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 Mount Pleasant
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 Mount Pleasant 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 |
|---|---|---|---|---|
| One-Family Residential | 0.9183 ac | — | 35 ft | Occupancy restricted |
| Planned Residential Historic Dev. Transitional | 6 ac | — | 40 ft | No |
| Planned Residential Development Transitional | 3 ac | — | 40 ft | No |
| Planned Residential Development Transitional | 4 ac | — | 40 ft | No |
| Planned Residential Development Transitional | 3 ac | — | 35 ft | No |
| Planned Residential Development Transitional | 0.1148 ac | — | 35 ft | No |
| One-Family Residential | 0.2296 ac | — | 35 ft | Occupancy restricted |
| One-Family Residential | 0.4591 ac | — | 35 ft | Occupancy restricted |
| Multifamily Residential | 0.2296 ac | — | 40 ft | No |
| Multifamily Residential | 0.2296 ac | — | 40 ft | No |
| Planned Residential Development Transitional | 2.4 ac | — | 35 ft | No |
| Planned Light Industry | — | — | 40 ft | No |
| General Office Building | 25 ac | — | 65 ft | No |
| Public Utility Office Building | 20 ac | — | 40 ft | No |
| Research Office Building | 25 ac | — | 65 ft | No |
| Office Business | 25 ac | — | 65 ft | No |
| OB-6 | 10 ac | — | 40 ft | No |
| General Commercial | — | — | 45 ft | No |
| Neighborhood Retail | 0.2296 ac | — | 35 ft | No |
| Rural Business | 0.9183 ac | — | 35 ft | No |
| Office Business Transitional | 1 ac | — | 40 ft | No |
| Office Business Transitional | 6 ac | — | 40 ft | No |
| Office Business Transitional | 7 ac | — | 40 ft | No |
| Office Business Transitional | 1 ac | — | 40 ft | No |
| Hawthorne Hamlet | — | — | — | No |
| Valhalla Hamlet | 0.2296 ac | — | 35 ft | No |
| Light Industry | — | — | 40 ft | No |
| Corporate Office Education | 50 ac | — | 45 ft | No |
| Planned Shopping | — | — | — | No |
| Floating Zone | — | — | — | — |
| Hawthorne Hamlet | — | — | — | No |
| Hawthorne Hamlet Core | — | — | — | No |
Size limits on record in Mount Pleasant
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 Mount Pleasant:
- One-Family ResidentialR-40 is one of the three One-Family Residential Districts of § 218-4, so § 218-36 reaches it. Planning Board accessory apartment permit, issued ONLY to the owner-occupant of the principal dwelling and lapsing automatically on a change of ownership or when the owner stops occupying — a new owner has ten days from taking title to apply (§ 218-36A, B). Principal dwelling only, which must have existed at least 10 years (C); maximum 25% of the dwelling or 600 sq ft, whichever is less (D); one per lot (E); lot must meet the district minimum (K); and the dwelling must be served by both public sewer and public water (H).
- One-Family ResidentialR-10 is one of the three One-Family Residential Districts of § 218-4, so § 218-36 reaches it. Planning Board permit issued only to the owner-occupant, lapsing automatically on a change of ownership or when the owner ceases to occupy, with ten days for a new owner to apply (§ 218-36A, B). Principal dwelling only and at least 10 years old (C); maximum 25% of the dwelling or 600 sq ft, whichever is less (D); one per lot; lot no smaller than the district minimum (K); both public sewer and public water required (H).
- One-Family ResidentialR-20 is one of the three One-Family Residential Districts of § 218-4, so § 218-36 reaches it. Planning Board permit issued only to the owner-occupant, lapsing automatically on a change of ownership or when the owner ceases to occupy, with a ten-day window for a new owner to apply (§ 218-36A, B). Principal dwelling only and at least 10 years old (C); maximum 25% of the dwelling or 600 sq ft, whichever is less (D); one per lot; lot no smaller than the district minimum (K); public sewer AND public water required (H).
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 rentalsShort-term rentals prohibited. Short-term rentals are BANNED. § 218-20.6 of the Zoning Code, titled 'Short-term rentals prohibited', was added 1-24-2023 by L.L. No. 1-2023 and applies to the rental of properties throughout the Town. The section defines an immediate family member, so an arrangement with relatives may sit outside the prohibition — confirm any such reading with the Town. Tourist homes are treated separately at § 218-56 and motels at § 218-42. New York State's 2025 short-term rental registry (Ch. 99 of the Laws of 2025) separately requires every host statewide to register the unit regardless of local law. Confirm with Town of Mount Pleasant at (914) 742-2305 before listing. Separate question from whether you can build the unit.
- Building dept(914) 742-2305
Sizing up a specific parcel in Mount Pleasant?
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 Mount Pleasant runs $242–318/sq ft, about $435k–570k at 1,800 sq ft . See what it costs to build a house in Mount Pleasant.
ADU cost in nearby towns
All Westchester County towns: Harrison (City) · Mount Vernon (City) · New Rochelle (City) · Peekskill (City) · Rye (City) · White Plains (City) · Yonkers (City) · Bedford · Cortlandt · Eastchester · Greenburgh · Lewisboro · Mamaroneck · 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 Mount Pleasant: Can you build an ADU here? · Zoning for new construction · Westchester County build cost
ADU cost in Mount Pleasant: common questions
How much does it cost to build an ADU in Mount Pleasant, NY?
An 800 sq ft accessory dwelling unit in Town of Mount Pleasant 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 Mount Pleasant?
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 Mount Pleasant?
Town of Mount Pleasant has 32 districts. 28 districts prohibit ADUs, 3 allow them with occupancy restrictions. 1 district has incomplete data - verify with the building department at (914) 742-2305. Check the specific address with the free ADU checker before you spend money on design.
Can I rent an ADU in Mount Pleasant short term?
Short-term rentals prohibited for Town of Mount Pleasant. 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 Mount Pleasant vary by district and often carry exceptions this page does not show; zoning last reviewed 2026-06-15; verify with the building department at (914) 742-2305 before relying on any answer. Sources: Offsite / Aldo cost engine (costEngine.js + constants.js); zoning dataset (municipalData.js).