Southeast · ADU cost
What it costs to build an ADU in Southeast, NY
An 800 sq ft accessory dwelling unit in Southeast runs roughly $215k–285k, or about $271–355/sq ft, and that per-square-foot figure sits deliberately above the $222–291/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 Southeast maps 19 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 Southeast
Standard finish, slab on grade, on a flat and clear part of the lot, general-contractor margin included. These are structure costs at Putnam County pricing, before the service and septic work a second dwelling can trigger.
| Size | Type | $ / sq ft | Estimated total |
|---|---|---|---|
| 400 sq ft | Studio | $360–$471 | $145k–190k |
| 600 sq ft | One bedroom | $301–$394 | $180k–235k |
| 800 sq ft | One bedroom, larger | $271–$355 | $215k–285k |
| 1,000 sq ft | Two bedroom | $254–$332 | $255k–330k |
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–$25 | $18 | — |
| Framing | $28–$35 | $28 | — |
| Envelope - roof, siding, windows | $35–$45 | $35 | — |
| Plumbing | $30–$37 | $18 | 55% |
| Electrical | $20–$26 | $14 | 35% |
| HVAC | $25–$31 | $16 | 45% |
| Insulation | $8–$10 | $8 | — |
| Interior finishes | $35–$47 | $30 | 15% |
| Millwork & cabinetry | $20–$30 | $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 Southeast 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 |
|---|---|---|---|---|
| Residence (use group p: min lot width 300 ft; combined side yards 200 ft; required street frontage 250 ft; FAR 0.20). Accessory apartments and short-term rentals are both listed uses here | 3.67 ac | 100 / 100 / 100 ft | 35 ft | As of right |
| Residence (use group a: min lot width 200 ft; combined side yards 100 ft; required street frontage 175 ft; FAR 0.20). NOTE: short-term rental is NOT listed for R-80, though accessory apartments are (as a conditional use) | 1.84 ac | 50 / 30 / 50 ft | 35 ft | Special permit |
| Residence (use group b: min lot width 175 ft; combined side yards 75 ft; required street frontage 175 ft; FAR 0.20). Inherits R-80's conditional uses; short-term rental is a conditional use here | 1.38 ac | 50 / 30 / 50 ft | 35 ft | Special permit |
| Residence (use group c: min lot width 135 ft; combined side yards 70 ft; required street frontage 135 ft; FAR 0.20). Inherits R-80's conditional uses; short-term rental is a conditional use here | 0.92 ac | 50 / 25 / 50 ft | 35 ft | Special permit |
| Residence (use group d: min lot width 90 ft; combined side yards 50 ft; required street frontage 90 ft; FAR 0.25). Inherits R-80's conditional uses; short-term rental is a conditional use here | 0.46 ac | 35 / 20 / 35 ft | 35 ft | Special permit |
| Residence Multifamily (use group e: min lot width 90 ft; combined side yards 50 ft; required street frontage 90 ft; FAR 0.25. Multiple dwellings are permitted subject to § 138-23). Short-term rental is a conditional use here | 0.46 ac | 35 / 20 / 35 ft | 35 ft | Special permit |
| Lake Tonetta Watershed (use group g: a low-intensity watershed-protection district — min lot area 10 acres, min lot width 400 ft, combined side yards 200 ft, and maximum lot coverage of just 3%. Single-family dwellings and accessory apartments are permitted by right; short-term rental is a conditional use) | 10 ac | 100 / 100 / 100 ft | 35 ft | As of right |
| Neighborhood Business (min lot 10,000 sf / 50 ft frontage / 50 ft width / 50 ft depth; a public-water-and-sewer alternative allows 20,000 sf on 90 ft. Setbacks are the parking-setback figures where the schedule leaves principal yards to site plan). Bed-and-breakfast/country inn is a principal use | 0.23 ac | 35 / 35 / 35 ft | 30 ft | No |
| Economic Development (min lot 80,000 sf / 200 ft frontage / 200 ft width / 200 ft depth; FAR 0.30). Light manufacturing and research labs are special-permit uses | 1.84 ac | 100 / 50 / 75 ft | 35 ft | No |
| Office Park (min lot 120,000 sf / 250 ft frontage / 250 ft width / 250 ft depth; FAR 0.25; 3 stories) | 2.75 ac | 100 / 50 / 50 ft | 45 ft | No |
| Office Park (min lot 200,000 sf / 400 ft frontage / 400 ft width / 400 ft depth; FAR 0.25; 3 stories) | 4.59 ac | 100 / 50 / 50 ft | 45 ft | No |
| Office Park (min lot 100,000 sf / 400 ft frontage / 400 ft width / 400 ft depth; FAR 0.25; 3 stories) | 2.3 ac | 100 / 50 / 50 ft | 45 ft | No |
| Gateway Commercial (min lot 10,000 sf / 50 ft frontage / 50 ft width / 50 ft depth; FAR 0.40; 2 stories) | 0.23 ac | 35 / 35 / 35 ft | 30 ft | No |
| Special Route 6 Area (min lot 30,000 sf / 25 ft frontage / 50 ft width / 50 ft depth; FAR 0.40; 2 stories) | 0.69 ac | 35 / 35 / 35 ft | 30 ft | No |
| Highway Commercial (min lot 40,000 sf / 150 ft frontage / 150 ft width / 150 ft depth; FAR 0.30; 2 stories) | 0.92 ac | 50 / 35 / 35 ft | 35 ft | No |
| Special Route 22 Area (min lot 80,000 sf / 250 ft frontage / 250 ft width / 250 ft depth; FAR 0.25; 3 stories) | 1.84 ac | 50 / 25 / 25 ft | 45 ft | No |
| Rural Commercial 2 (min lot 80,000 sf / 250 ft frontage / 250 ft width / 250 ft depth; FAR 0.25; 3 stories). Single-family residential is a permitted use and accessory apartment appears as a use | 1.84 ac | 50 / 25 / 25 ft | 45 ft | No |
| Rural Commercial (min lot 200,000 sf / 400 ft frontage / 400 ft width / 400 ft depth; FAR 0.15; maximum lot coverage 15% building / 45% total; 3 stories). Single-family residential is a permitted use here | 4.59 ac | 100 / 100 / 100 ft | 35 ft | No |
| General Commercial 2 (min lot 40,000 sf / 100 ft frontage / 100 ft width / 50 ft depth; FAR 0.40; 2 stories). Bed-and-breakfast/country inn is a principal use and accessory apartment appears as a conditional use | 0.92 ac | 50 / 50 / 50 ft | 30 ft | No |
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 NYSEG 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 allowed with local rules. Short-term rental is a defined and regulated use in the Town of Southeast. In the Table of General Use Requirements for the residential districts, 'short-term rental' is a CONDITIONAL use requiring Planning Board approval in R-160, R-60, R-40, R-20, RMF and LTW; it is notably NOT listed for R-80. Bed-and-breakfast and country inn are separate, distinct uses (e.g. bed-and-breakfast is by right in R-160 and appears across several commercial districts). Because STR requires case-by-case Planning Board approval rather than being either by-right or prohibited, it is recorded as regulated. Separately, since 2025 New York State requires every short-term-rental host to register the unit with the State through the county registry, regardless of what the municipality allows. Separate question from whether you can build the unit.
- Building dept(845) 279-2123
Sizing up a specific parcel in Southeast?
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 Southeast runs $222–291/sq ft, about $400k–525k at 1,800 sq ft , plus roughly $18,005 for a conforming lot. See what it costs to build a house in Southeast.
ADU cost in nearby towns
All Putnam County towns: Carmel · Kent · Patterson · Philipstown · Putnam Valley · Brewster (Village) · Cold Spring (Village) · Nelsonville (Village)
More on Southeast: Can you build an ADU here? · Zoning for new construction · Putnam County build cost
ADU cost in Southeast: common questions
How much does it cost to build an ADU in Southeast, NY?
An 800 sq ft accessory dwelling unit in Town of Southeast runs roughly $215k–285k at a standard finish, general-contractor margin included. A 400 sq ft studio runs about $145k–190k. 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 Southeast?
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 $271–355/sq ft against $222–291/sq ft for a full house, even though it is the same trades doing the same work.
Are ADUs allowed in Southeast?
Town of Southeast has 19 districts. 12 districts prohibit ADUs, 5 require a special-use permit, 2 allow them. Check the specific address with the free ADU checker or confirm with the building department at (845) 279-2123 before you spend money on design.
Can I rent an ADU in Southeast short term?
Short-term rentals allowed with local rules for Town of Southeast. 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 Putnam 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 Southeast vary by district and often carry exceptions this page does not show; zoning last reviewed 2026-07-23; verify with the building department at (845) 279-2123 before relying on any answer. Sources: Offsite / Aldo cost engine (costEngine.js + constants.js); zoning dataset (municipalData.js).