Patterson · ADU cost
What it costs to build an ADU in Patterson, NY
An 800 sq ft accessory dwelling unit in Patterson 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 Patterson maps 9 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 Patterson
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 Patterson 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 |
|---|---|---|---|---|
| Putnam Lake Residence (min lot 19,500 sf; 75 ft minimum road frontage; 15 ft front, 15 ft side, 20 ft rear; 38% maximum IMPERVIOUS surface coverage — Patterson sets no building-coverage percentage; 38 ft height; minimum livable first-floor area 750 sf for dwelling purposes. The Town's densest residential district, covering the Putnam Lake community. Accessory structures of 120 sf or less and under 10 ft high need 5 ft side and rear setbacks; larger or taller accessory structures need 10 ft) | 0.45 ac | 15 / 15 / 20 ft | 38 ft | Special permit |
| Residence 1 — one-acre (min lot 43,560 sf / 1 acre; 100 ft minimum road frontage; 150 ft average lot width; 35 ft front, 30 ft side, 50 ft rear; 12% maximum IMPERVIOUS surface coverage — no building-coverage percentage is set; 38 ft height; minimum livable first-floor area 1,000 sf. Accessory structures: 35 ft front, 15 ft side, 25 ft rear) | 1 ac | 35 / 30 / 50 ft | 38 ft | Special permit |
| Residence 2 — two-acre (min lot 87,120 sf / 2 acres; 175 ft minimum road frontage; 200 ft average lot width; 40 ft front, 40 ft side, 50 ft rear; 10% maximum IMPERVIOUS surface coverage; 38 ft height; minimum livable first-floor area 1,000 sf. Accessory structures: 40 ft front, 20 ft side, 25 ft rear) | 2 ac | 40 / 40 / 50 ft | 38 ft | Special permit |
| Residence 4 — four-acre (min lot 174,240 sf / 4 acres; 225 ft minimum road frontage; 250 ft average lot width; 40 ft front, 40 ft side, 80 ft rear; 10% maximum IMPERVIOUS surface coverage; 38 ft height; minimum livable first-floor area 1,000 sf. The Town's lowest-density district. Accessory structures: 40 ft front, 20 ft side, 25 ft rear) | 4 ac | 40 / 40 / 80 ft | 38 ft | Special permit |
| General Business (min lot 30,000 sf; 100 ft minimum road frontage; 15 ft front, 15 ft side, 25 ft rear; 65% maximum IMPERVIOUS surface coverage; 38 ft height; minimum floor area 900 sf. § 154 permits a building in the GB district to contain one or more apartments subject to conditions — that is a permitted apartment use, not an accessory apartment. Accessory structures: 25 ft front, 10 ft side, 10 ft rear) | 0.69 ac | 15 / 15 / 25 ft | 38 ft | No |
| Commercial 1 (min lot 87,120 sf / 2 acres; 200 ft minimum road frontage; 65 ft front, 30 ft side, 50 ft rear; 65% maximum IMPERVIOUS surface coverage; 35 ft height; minimum floor area 1,500 sf. Accessory structures: 40 ft front, 20 ft side, 30 ft rear) | 2 ac | 65 / 30 / 50 ft | 35 ft | No |
| Industrial (min lot 87,120 sf / 2 acres; 200 ft minimum road frontage; 65 ft front, 30 ft side, 50 ft rear; 65% maximum IMPERVIOUS surface coverage; 35 ft height; minimum floor area 1,500 sf. Accessory structures: 40 ft front, 20 ft side, 30 ft rear) | 2 ac | 65 / 30 / 50 ft | 35 ft | No |
| Commercial Recreation (min lot 200 ACRES — by far the largest minimum in the county; 200 ft minimum road frontage; 65 ft front, 30 ft side, 50 ft rear; 25% maximum IMPERVIOUS surface coverage; 35 ft height. A destination-scale district for golf courses, country clubs, conference and cultural centers. Accessory structures: 40 ft front, 20 ft side, 30 ft rear) | 200 ac | 65 / 30 / 50 ft | 35 ft | No |
| Open Space Overlay District (minimum lot size is set by § 138-49.A of the Subdivision chapter rather than by a fixed figure in the Zoning Schedule, so no numeric minimum is recorded; 125 ft minimum road frontage; 150 ft average lot width; 35 ft front, 30 ft side, 40 ft rear; 20% maximum IMPERVIOUS surface coverage; 35 ft height; minimum livable first-floor area 1,000 sf. Lots in this overlay must ALSO comply with Chapter 138, Part 2, which imposes additional restrictions on top of the underlying residence district's requirements — the overlay is additive, never a relaxation) | — | 35 / 30 / 40 ft | 35 ft | Special permit |
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 registration. A rental permit is required, and it is NOT in the zoning chapter. Chapter 129, the Rental Registration Law (L.L. No. 9-2007, effective 1-30-2008), requires a permit for every rental dwelling unit under § 129-4, with application, fee, review, term and renewal at §§ 129-5 through 129-8 and a public register at § 129-9. There is no minimum-stay exclusion: § 129-6C sets a distinct fee tier for hotel/motel businesses catering to transient clientele and defines a 'short duration of time' as not more than 21 consecutive days, which prices short stays rather than exempting them. § 129-10 conditions the permit on a working smoke detector, on-site parking, a minimum 100 square feet for a one-room unit, and independent kitchen facilities in each unit, and § 129-11 authorises inspections on consent. Zoning Chapter 154 separately permits a BED-AND-BREAKFAST INN under § 154-102 — owner-occupied, with 'transient' defined at § 154-115 as not more than 14 consecutive days or 28 days a year. 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 Patterson at (845) 878-6500 before listing. Separate question from whether you can build the unit.
- Building dept(845) 878-6500
Sizing up a specific parcel in Patterson?
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 Patterson runs $222–291/sq ft, about $400k–525k at 1,800 sq ft , plus roughly $13,649 for a conforming lot. See what it costs to build a house in Patterson.
ADU cost in nearby towns
All Putnam County towns: Carmel · Kent · Philipstown · Putnam Valley · Southeast · Brewster (Village) · Cold Spring (Village) · Nelsonville (Village)
More on Patterson: Can you build an ADU here? · Zoning for new construction · Putnam County build cost
ADU cost in Patterson: common questions
How much does it cost to build an ADU in Patterson, NY?
An 800 sq ft accessory dwelling unit in Town of Patterson 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 Patterson?
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 Patterson?
Town of Patterson has 9 districts. 5 districts allow ADUs with a special-use permit, 4 do not. Check the specific address with the free ADU checker or confirm with the building department at (845) 878-6500 before you spend money on design.
Can I rent an ADU in Patterson short term?
Short-term rentals allowed with registration for Town of Patterson. 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 Patterson vary by district and often carry exceptions this page does not show; zoning last reviewed 2026-07-27; verify with the building department at (845) 878-6500 before relying on any answer. Sources: Offsite / Aldo cost engine (costEngine.js + constants.js); zoning dataset (municipalData.js).