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Delaware · ADU cost

What it costs to build an ADU in Delaware, NY

800 sq ft ≈ $190k–250k $238–312/sq ft 7 districts NYSEG

An 800 sq ft accessory dwelling unit in Delaware runs roughly $190k–250k, or about $238–312/sq ft, and that per-square-foot figure sits deliberately above the $195–256/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 Delaware 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 Delaware

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

SizeType$ / sq ftEstimated total
400 sq ft Studio $316–$414 $125k–165k
600 sq ft One bedroom $264–$346 $160k–210k
800 sq ft One bedroom, larger $238–$312 $190k–250k
1,000 sq ft Two bedroom $223–$292 $225k–290k

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 $7–$10 $7 —
Foundation $16–$22 $16 —
Framing $24–$30 $24 —
Envelope - roof, siding, windows $30–$39 $30 —
Plumbing $26–$32 $16 55%
Electrical $18–$23 $12 35%
HVAC $22–$27 $14 45%
Insulation $7–$9 $7 —
Interior finishes $31–$41 $26 15%
Millwork & cabinetry $18–$26 $10 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 Delaware 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
Delaware River District 2 ac 50 / 50 / 50 ft 35 ft No
Residential District 0.92 ac 50 / 30 / 50 ft 35 ft No
Rural District 1.84 ac 50 / 30 / 50 ft 45 ft No
Business District 0.17 ac 20 / 10 / 30 ft 60 ft No
Callicoon Business District 2 ac 50 / 25 / 25 ft 40 ft No
Callicoon Residential District 0.92 ac 50 / 30 / 50 ft 35 ft No
Planned Unit Development District 0.92 ac 50 / 30 / 50 ft 45 ft No

Delaware River District - The Delaware River District asks 2 acres, a 200 foot lot width and depth, 50 feet front, 50 feet to one side with 100 feet for both sides, and 50 feet rear. Building height stops at 35 feet and lot coverage at 10,000 square feet or 15%, whichever is less.

  • Residential density may not exceed one dwelling unit per two acres.
  • No building, structure or part of a septic system may stand within 100 feet of the normal high water mark of the Delaware River, and a new lot bordering the river needs 200 feet of frontage along it.
  • On a street whose right of way is under 50 feet, the front yard is measured from the center line of the roadway and 25 feet is added.
  • Cluster development is a special use on a contiguous parcel of at least 5 acres.
  • A cluster lot on on-site water or sewage may fall to 0.9183 acre, with 150 feet of width and depth, 25% coverage and yards of 50 feet front, 30 feet side and 50 feet rear.
  • A cluster lot on central water and sewage may fall to 0.2296 acre, with 70 feet of width, 100 feet of depth, 35% coverage and yards of 25 feet front, 10 feet side and 15 feet rear.

Residential District - The Residential District asks 40,000 square feet, a 150 foot lot width and depth, 50 feet front, 30 feet to one side with 70 feet for both sides, and 50 feet rear. Building height stops at 35 feet and lot coverage at 25%.

  • On central water and central sewage the minimums drop by 50%: 0.4591 acre, 75 feet of width and depth, and yards of 25 feet front, 15 feet one side, 35 feet both sides and 25 feet rear.
  • A two family dwelling needs 1.5 times the single family lot minimum, which is 1.3774 acres.
  • Converting an existing building to a two family dwelling keeps the single family minimum of 0.9183 acre.
  • A multiple dwelling project is a special use, must be served by central water and central sewage, and counts 20,000 square feet of land for each dwelling unit.
  • Cluster development is a special use on a contiguous parcel of at least 5 acres served by central water and central sewage.
  • A cluster lot may fall to 0.2296 acre, with 70 feet of width, 100 feet of depth, 35% coverage and yards of 25 feet front, 10 feet side and 15 feet rear.

Rural District - The Rural District asks 80,000 square feet, a 200 foot lot width and depth, 50 feet front, 30 feet to one side with 70 feet for both sides, and 50 feet rear. Building height stops at 45 feet and lot coverage at 15%.

  • On central water and central sewage the minimums drop by 50%: 0.9183 acre, 100 feet of width and depth, and yards of 25 feet front, 15 feet one side, 35 feet both sides and 25 feet rear.
  • The special uses the schedule marks with an asterisk need at least 4 acres.
  • A two family dwelling needs twice the single family lot minimum, which is 3.6731 acres, while converting an existing building to one keeps 1.8365 acres.
  • Cluster development is a special use on a contiguous parcel of at least 5 acres.
  • A cluster lot on on-site water or sewage may fall to 0.9183 acre, with 150 feet of width and depth, 25% coverage and yards of 50 feet front, 30 feet side and 50 feet rear.
  • A cluster lot on central water and sewage may fall to 0.2296 acre, with 70 feet of width, 100 feet of depth, 35% coverage and yards of 25 feet front, 10 feet side and 15 feet rear.

Business District - The Business District asks 7,500 square feet, a 50 foot lot width, a 100 foot lot depth, 20 feet front, 10 feet to one side with 20 feet for both sides, and 30 feet rear. Building height stops at 60 feet and lot coverage at 65%.

  • The front yard may be reduced to line up with adjacent buildings.
  • Residential development follows the Residential District standards: 0.9183 acre, 150 feet of width and depth, and yards of 50 feet front, 30 feet one side, 70 feet both sides and 50 feet rear.
  • Residential building height there stops at 35 feet and residential lot coverage at 25%.
  • A two family dwelling needs 1.5 times that single family minimum, which is 1.3774 acres.
  • A multiple dwelling project is a special use, must be served by central water and central sewage, and counts 5,000 square feet of land for each dwelling unit.
  • Cluster development is not available in this district.

Callicoon Business District - The Callicoon Business District asks 2 acres without central water and sewage, a 200 foot lot width and depth, 50 feet front, 25 feet side and 25 feet rear. Building height stops at 40 feet and lot coverage at 65%.

  • On central water and central sewage the lot minimum is 0.2296 acre, with 50 feet of width, 100 feet of depth, and yards of 20 feet front, 10 feet one side, 20 feet both sides and 30 feet rear.
  • The front yard may be reduced to line up with adjacent buildings.
  • On the downtown Callicoon parcels the front yard is zero feet, side yards are 5 feet each and the rear yard is 10 feet, with building coverage at 85% and lot coverage at 100%.
  • A two family dwelling needs 1.5 times the single family lot minimum, which is 3 acres without central water and sewage and 0.3444 acre with them.
  • A multiple dwelling project is a special use, must be served by central water and central sewage, and counts 7,500 square feet of land for each dwelling unit.
  • No building, structure or part of a septic system may stand within 100 feet of the normal high water mark of the Delaware River, and a new lot bordering the river needs 200 feet of frontage along it.

Callicoon Residential District - The Callicoon Residential District takes the Residential District figures: 40,000 square feet, a 150 foot lot width and depth, 50 feet front, 30 feet to one side with 70 feet for both sides, and 50 feet rear. Building height stops at 35 feet and lot coverage at 25%.

  • On central water and central sewage the minimums drop by 50%: 0.4591 acre, 75 feet of width and depth, and yards of 25 feet front, 15 feet one side, 35 feet both sides and 25 feet rear.
  • A two family dwelling needs 1.5 times the single family lot minimum, which is 1.3774 acres, while converting an existing building to one keeps 0.9183 acre.
  • A multiple dwelling project is a special use, must be served by central water and central sewage, and counts 20,000 square feet of land for each dwelling unit.
  • Cluster development is a special use on a contiguous parcel of at least 5 acres served by central water and central sewage, and its lots may fall to 0.2296 acre.
  • A cluster lot takes 70 feet of width, 100 feet of depth, 35% coverage and yards of 25 feet front, 10 feet side and 15 feet rear.
  • No building, structure or part of a septic system may stand within 100 feet of the normal high water mark of the Delaware River, and a new lot bordering the river needs 200 feet of frontage along it.

Planned Unit Development District - The Planned Unit Development District allows 2 dwelling units or equivalent dwelling units per acre. Building height stops at 45 feet and lot coverage at 15%. Every use must be served by central water and central sewage, and every use is a special use.

  • The schedule publishes no lot area, width, depth or yard minimum for this district.
  • The district tract must cover at least 50 contiguous acres, though a smaller tract may be approved.
  • A building site no closer than 300 feet to the property borders may reach 60 feet in height.
  • A single family dwelling on on-site water or sewage follows the Residential District standards: 0.9183 acre, 150 feet of width and depth, 35 feet of height and 25% coverage.
  • Its yards are then 50 feet front, 30 feet to one side with 70 feet for both sides, and 50 feet rear.
  • Cluster development is a special use on at least 5 acres, with lots to 0.2296 acre, 70 feet of width, 100 feet of depth, 35% coverage and yards of 25 feet front, 10 feet side and 15 feet rear.
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Costs an ADU adds that a house does not

Sizing up a specific parcel in Delaware?

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Building a full house instead?

A standard-finish house in Delaware runs $195–256/sq ft, about $350k–460k at 1,800 sq ft , plus roughly $9,367 for a conforming lot. See what it costs to build a house in Delaware.

ADU cost in nearby towns

Bethel
800 sq ft ≈ $190k–250k
Callicoon
800 sq ft ≈ $190k–250k
Cochecton
800 sq ft ≈ $190k–250k
Fallsburg
800 sq ft ≈ $190k–250k
Forestburgh
800 sq ft ≈ $190k–250k
Fremont
800 sq ft ≈ $190k–250k

All Sullivan County towns: Bethel · Callicoon · Cochecton · Fallsburg · Forestburgh · Fremont · Highland · Liberty · Lumberland · Mamakating · Neversink · Rockland · Thompson · Tusten · Bloomingburg (Village) · Jeffersonville (Village) · Liberty (Village) · Monticello (Village) · Woodridge (Village)

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

ADU cost in Delaware: common questions

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

An 800 sq ft accessory dwelling unit in Town of Delaware runs roughly $190k–250k at a standard finish, general-contractor margin included. A 400 sq ft studio runs about $125k–165k. 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 Delaware?

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 $238–312/sq ft against $195–256/sq ft for a full house, even though it is the same trades doing the same work.

Are ADUs allowed in Delaware?

Town of Delaware has 7 districts. All districts prohibit ADUs. Check the specific address with the free ADU checker or confirm with the building department at (845) 887-5250 before you spend money on design.

Can I rent an ADU in Delaware short term?

Short-term rentals allowed with local rules for Town of Delaware. 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 Sullivan 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 Delaware vary by district and often carry exceptions this page does not show; zoning last reviewed 2026-10-07; verify with the building department at (845) 887-5250 before relying on any answer. Sources: the Offsite / Aldo cost engine and zoning dataset.

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