New Hempstead · ADU cost
What it costs to build an ADU in New Hempstead, NY
An 800 sq ft accessory dwelling unit in New Hempstead runs roughly $225k–295k, or about $280–366/sq ft, and that per-square-foot figure sits deliberately above the $229–300/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 village 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 Village of New Hempstead maps 7 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 New Hempstead
Standard finish, slab on grade, on a flat and clear part of the lot, general-contractor margin included. These are structure costs at Rockland County pricing, before the service and septic work a second dwelling can trigger.
| Size | Type | $ / sq ft | Estimated total |
|---|---|---|---|
| 400 sq ft | Studio | $371–$485 | $150k–195k |
| 600 sq ft | One bedroom | $310–$406 | $185k–245k |
| 800 sq ft | One bedroom, larger | $280–$366 | $225k–295k |
| 1,000 sq ft | Two bedroom | $261–$342 | $260k–340k |
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 | $8–$12 | $8 | — |
| Foundation | $18–$26 | $18 | — |
| Framing | $29–$36 | $29 | — |
| Envelope - roof, siding, windows | $36–$46 | $36 | — |
| Plumbing | $31–$38 | $18 | 55% |
| Electrical | $21–$26 | $14 | 35% |
| HVAC | $26–$32 | $16 | 45% |
| Insulation | $8–$10 | $8 | — |
| Interior finishes | $36–$48 | $31 | 15% |
| Millwork & cabinetry | $21–$31 | $12 | 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 New Hempstead 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 Residence | 1.15 ac | 50 / 30 / 50 ft | 35 ft | No |
| One-Family Residence | 0.92 ac | 50 / 25 / 50 ft | 35 ft | No |
| One-Family Residence | 0.8 ac | 50 / 25 / 50 ft | 35 ft | No |
| One-Family Residence | 0.57 ac | 35 / 20 / 35 ft | 35 ft | No |
| One- and Two-Family Residence | 0.34 ac | 35 / 20 / 35 ft | 35 ft | No |
| Laboratory-Office | 1.38 ac | 75 / 75 / 75 ft | 45 ft | No |
| Neighborhood Commercial | 2 ac | 75 / 50 / 50 ft | 35 ft | No |
One-Family Residence - The 20% coverage figure is the maximum impervious surface ratio, counting drives, terraces and every other hard surface along with the buildings. A building must meet the floor area ratio or a 3,750 sq ft building coverage cap, not both, and the owner chooses which.
- An average density subdivision is a second complete row: 0.9183 acres on 150 ft of width, 25 ft to each side with 70 ft for the pair. Minimum lot frontage is 100 ft, separate from lot width.
- An active adult community, a special permit use under § 290-57, is capped at 120 units; a single-story home sits on 0.1148 acres with 10 ft to each side, two storeys and 10% coverage.
- A respite facility for disabled children needs 10 acres, 435,600 sq ft, on 250 ft of width with 30 ft each side; a preexisting building 15 feet from a line, or an accessory 3 feet, is exempt.
- No land inside an access easement or right-of-way counts toward a minimum lot area, and the lot area rules bind existing easements as well as proposed ones.
- Only a quarter of land under water, in a village wetland, hundred-year floodplain or open drainage easement, under overhead utility lines or unexcavated over 25% slope counts toward the lot minimum.
- Only three quarters of land in a conservation easement, a piped drainage easement, a sewer easement or an underground utility easement counts toward a minimum lot area.
One-Family Residence - The 20% coverage figure is the maximum impervious surface ratio, counting drives, terraces and every other hard surface along with the buildings. A building must meet the floor area ratio or a 3,500 sq ft building coverage cap, not both, and the owner chooses which.
- An average density subdivision keeps the same 150 ft width on 0.8035 acres with 25 ft to each side and 60 ft for the pair, and raises the floor area ratio to 0.12.
- An active adult community, a special permit use under § 290-57, is capped at 120 units; a single-story home sits on 0.1148 acres with 10 ft to each side, two storeys and 10% coverage.
- A respite facility for disabled children needs 10 acres, 435,600 sq ft, on 250 ft of width with 30 ft each side; a preexisting building 15 feet from a line, or an accessory 3 feet, is exempt.
- Minimum lot frontage is 100 ft, separate from lot width. The Planning Board may reduce it for a residential lot on a cul-de-sac or a street curving at a radius of a hundred feet or less.
- Only a quarter of land under water, in a village wetland, hundred-year floodplain or open drainage easement, under overhead utility lines or unexcavated over 25% slope counts toward the lot minimum.
- Only three quarters of land in a conservation easement, a piped drainage easement, a sewer easement or an underground utility easement counts toward a minimum lot area.
One-Family Residence - The 20% coverage figure is the maximum impervious surface ratio, counting drives, terraces and every other hard surface along with the buildings. A building must meet the floor area ratio or a 3,250 sq ft building coverage cap, not both, and the owner chooses which.
- An average density subdivision is a second complete row: 0.5739 acres on 125 ft of width, 20 ft to each side with 50 ft for the pair, 35 ft front and rear, and a floor area ratio of 0.15.
- An active adult community, a special permit use under § 290-57, is capped at 120 units; a single-story home sits on 0.1148 acres with 10 ft each side, two storeys and 10% coverage.
- A townhouse in such a community sits on 0.0459 acres with side yards of 0 ft on either side, 10 ft to the rear and 20 ft to the front, a lot depth of 45 feet and 45 percent coverage.
- A respite facility for disabled children needs 10 acres, 435,600 sq ft, on 250 ft of width with 30 ft each side; a preexisting building 15 feet from a line, or an accessory 3 feet, is exempt.
- Minimum lot frontage is 100 ft, separate from lot width. The Planning Board may reduce it for a residential lot on a cul-de-sac or a street curving at a radius of a hundred feet or less.
- Only a quarter of land under water, in a village wetland, hundred-year floodplain or open drainage easement, under overhead utility lines or unexcavated over 25% slope counts toward the lot minimum.
One-Family Residence - The 25% coverage figure is the maximum impervious surface ratio, counting drives, terraces and every other hard surface along with the buildings. A building must meet the floor area ratio or a 3,000 sq ft building coverage cap, not both, and the owner chooses which.
- An average density subdivision is a second complete row: 0.3444 acres on 100 ft of width, 20 ft to each side with 50 ft for the pair. Minimum lot frontage is 90 ft, separate from lot width.
- A respite facility for families of disabled children needs 10 acres, 435,600 square feet, on 250 ft of width and the same street frontage, with 30 ft to each side, by special permit under § 290-55.
- A preexisting building 15 feet or more from a property line, and a preexisting accessory building 3 feet or more from one, need not meet that row's figures.
- No land inside an access easement or right-of-way counts toward a minimum lot area, and the lot area rules bind existing easements as well as proposed ones.
- Only a quarter of land under water, in a village wetland, hundred-year floodplain or open drainage easement, under overhead utility lines or unexcavated over 25% slope counts toward the lot minimum.
- Only three quarters of land in a conservation easement, a piped drainage easement, a sewer easement or an underground utility easement counts toward a minimum lot area.
One- and Two-Family Residence - A two-family house has its own figures, with side yards of 15 ft a side and 40 ft for the pair instead of 20 and 50, in exchange for five thousand more square feet of land.
- A two-family detached house is permitted by right on 0.4591 acres and 125 ft of width and the same street frontage, with 15 ft a side and 40 ft for the pair, and its impervious ratio rises to 30%.
- Independent living for people with disabilities is a special permit use under § 290-56, in this district only: 4 acres on 350 ft of width, 20 ft a side with 60 ft for the pair, one storey and 25 ft.
- A respite facility for families of disabled children needs 10 acres, 435,600 square feet, on 250 ft of width; a preexisting building 15 feet from a line, or an accessory one 3 feet, need not comply.
- A building must meet the floor area ratio or a coverage cap of 2,500 sq ft for a one-family house and 2,750 for a two-family, not both; the 25% shown is the maximum impervious surface ratio.
- Minimum lot frontage is 85 ft, separate from lot width. The Planning Board may reduce it for a residential lot on a cul-de-sac or a street curving at a radius of a hundred feet or less.
- Only a quarter of land under water, in a village wetland, hundred-year floodplain or open drainage easement, under overhead utility lines or unexcavated over 25% slope counts toward the lot minimum.
Laboratory-Office - The 75% coverage figure is the maximum impervious surface ratio, counting drives, terraces and every other hard surface along with the buildings. Minimum lot frontage is 100 ft, a standard separate from the lot width.
- A respite facility for families of disabled children needs 10 acres, 435,600 square feet, on 250 ft of width and the same street frontage, by special permit under § 290-55.
- A preexisting building 15 feet or more from a property line, and a preexisting accessory building 3 feet or more from one, need not meet that row's figures.
- There is no storey limit here, only the 45 ft height.
- No land inside an access easement or right-of-way counts toward a minimum lot area, and the lot area rules bind existing easements as well as proposed ones.
- Only a quarter of land under water, in a village wetland, hundred-year floodplain or open drainage easement, under overhead utility lines or unexcavated over 25% slope counts toward the lot minimum.
- Only three quarters of land in a conservation easement, a piped drainage easement, a sewer easement or an underground utility easement counts toward a minimum lot area.
Neighborhood Commercial - Lot area has a maximum as well as a minimum: at least 2 acres and at most six acres, net of environmental deductions. Parcels may not be assembled afterwards to reach the threshold; the minimum is judged on lots as they existed when the local law was adopted.
- The 35 ft height is for a principal building; an accessory building is held to fifteen.
- Minimum lot frontage is 150 ft, a standard separate from the lot width.
- The 75% coverage figure is the maximum impervious surface ratio, counting drives, terraces and every other hard surface along with the buildings.
- A building must meet the floor area ratio or the building coverage cap, not both; the owner chooses which of the two to be held to on the application.
- No land inside an access easement or right-of-way counts toward a minimum lot area, and the lot area rules bind existing easements as well as proposed ones.
- Only a quarter of land under water, in a village wetland, hundred-year floodplain or open drainage easement, under overhead utility lines or unexcavated over 25% slope counts toward the lot minimum.
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 Orange & Rockland 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-rental status not confirmed. Short-term rental rules in the Village of New Hempstead are not confirmed. Confirm with the Building Department before listing a property. Separate question from whether you can build the unit.
- Zoning codeecode360.com/30180572
- Building dept(845) 354-8100
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Building a full house instead?
A standard-finish house in New Hempstead runs $229–300/sq ft, about $410k–540k at 1,800 sq ft , plus roughly $6,439 for a conforming lot. See what it costs to build a house in New Hempstead.
ADU cost in nearby towns
All Rockland County towns: Clarkstown · Haverstraw · Orangetown · Ramapo · Stony Point · Airmont (Village) · Chestnut Ridge (Village) · Grand View-on-Hudson (Village) · Haverstraw (Village) · Hillburn (Village) · Montebello (Village) · Nyack (Village) · Piermont (Village) · Pomona (Village) · Sloatsburg (Village) · Spring Valley (Village) · Suffern (Village) · Upper Nyack (Village) · Wesley Hills (Village) · West Haverstraw (Village)
More on New Hempstead: Can you build an ADU here? · Zoning for new construction · Rockland County build cost
ADU cost in New Hempstead: common questions
How much does it cost to build an ADU in New Hempstead, NY?
An 800 sq ft accessory dwelling unit in Village of New Hempstead runs roughly $225k–295k at a standard finish, general-contractor margin included. A 400 sq ft studio runs about $150k–195k. 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 New Hempstead?
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 $280–366/sq ft against $229–300/sq ft for a full house, even though it is the same trades doing the same work.
Are ADUs allowed in New Hempstead?
Village of New Hempstead has 7 districts. All districts prohibit ADUs. Check the specific address with the free ADU checker or confirm with the building department at (845) 354-8100 before you spend money on design.
Can I rent an ADU in New Hempstead short term?
Short-term-rental status not confirmed for Village of New Hempstead. 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 Rockland 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 Village of New Hempstead vary by district and often carry exceptions this page does not show; zoning last reviewed 2026-07-21; verify with the building department at (845) 354-8100 before relying on any answer. Sources: the Offsite / Aldo cost engine and zoning dataset.