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.
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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 | 0.45 ac | 15 / 15 / 20 ft | 38 ft | Special permit |
| Residence 1 | 1 ac | 35 / 30 / 50 ft | 38 ft | Special permit |
| Residence 2 | 2 ac | 40 / 40 / 50 ft | 38 ft | Special permit |
| Residence 4 | 4 ac | 40 / 40 / 80 ft | 38 ft | Special permit |
| General Business | 0.69 ac | 15 / 15 / 25 ft | 38 ft | No |
| Commercial 1 | 2 ac | 65 / 30 / 50 ft | 35 ft | No |
| Industrial | 2 ac | 65 / 30 / 50 ft | 35 ft | No |
| Commercial Recreation | 200 ac | 65 / 30 / 50 ft | 35 ft | No |
| Open Space Overlay District | — | 35 / 30 / 40 ft | 35 ft | Special permit |
Putnam Lake Residence - The 38% coverage cap is a maximum impervious surface coverage, counting buildings, paving and every other impervious cover together, so driveways and patios compete with the house for the same allowance.
- The town sets no separate building coverage percentage, so the impervious surface cap is the binding site constraint here.
- The 75 ft width figure is a minimum road frontage; this district states no average lot width.
- The 750 sq ft minimum is livable first floor area for dwelling purposes.
- Accessory structures of 120 sq ft or less and under 10 ft tall take a 5 ft side and rear setback; anything larger or taller takes 10 ft.
- The front yard for accessory structures is 15 ft.
Residence 1 - The 12% coverage cap applies to all impervious surface together, buildings, paving and every other impervious cover, so driveways and patios compete with the house footprint. Two width standards both bind: 150 ft average lot width and 100 ft minimum road frontage.
- The figure shown is average lot width; a lot can meet the 100 ft road frontage and still fail the 150 ft average width.
- No separate building coverage percentage is set, so the impervious surface cap is the binding site constraint and should be modelled directly.
- The 1,000 sq ft minimum livable area is a first floor requirement, so a two storey design must still deliver it at grade.
- Accessory structures follow their own yard standards rather than the principal building setbacks: 35 ft front, 15 ft side, 25 ft rear.
Residence 2 - The 10% coverage cap is a maximum impervious surface coverage, counting buildings, paving and every other impervious cover together. Lot width also has two standards that both bind: a 200 ft average lot width and a minimum road frontage of 175 ft.
- Road frontage must be at least 175 ft, and the 200 ft standard is an average width, so a lot can meet its frontage at the road and still fail on average width.
- Accessory structures have their own yard standards, separate from the principal building setbacks: 40 ft front, 20 ft side, 25 ft rear.
- The 1,000 sq ft minimum is livable first floor area for dwelling purposes.
- The town sets no building coverage percentage, so the impervious surface cap is the binding site constraint to plan against.
Residence 4 - Two width standards both apply here: the 250 ft figure is an average lot width, and a lot must also have at least 225 ft of road frontage. A lot can meet its frontage at the road and still fail on average width.
- The 10% coverage cap is a maximum impervious surface coverage, counting buildings, paving and every other impervious cover together.
- No separate building coverage percentage is set, so the impervious cap is the binding site constraint.
- Accessory structures have their own yard standards: 40 ft front, 20 ft side and 25 ft rear.
- The 1,000 sq ft minimum livable floor area is measured on the first floor used for dwelling purposes.
General Business - The 65% figure is a cap on total impervious surface, counting buildings, paving and every other hard cover together, so it is the binding limit on how much of the lot can be developed.
- No separate building coverage percentage applies in this town, so site plans should be modelled against the impervious surface cap.
- The 100 ft width figure is a minimum road frontage requirement; no average lot width is set for this district.
- Accessory structures have their own yard requirements, 25 ft front, 10 ft side and 10 ft rear, which differ from the principal building setbacks shown.
- The 900 sq ft minimum is a floor area requirement for the building, not a minimum livable first floor area for a dwelling.
Commercial 1 - The 65% coverage cap is a maximum impervious surface coverage, counting buildings, paving and every other impervious cover together, so parking and driveways eat into it. The 200 ft width figure is a minimum road frontage.
- No building coverage percentage is set, so the impervious surface cap is the binding site constraint and should be modelled directly.
- Accessory structures have their own yard requirements, separate from the principal building setbacks shown: 40 ft front, 20 ft side, 30 ft rear.
- The 1,500 sq ft figure is a minimum floor area for the building rather than a livable first floor area for dwelling purposes.
- This district states no average lot width requirement.
Industrial - The 65% coverage figure is a maximum impervious surface cap, counting buildings, paving and every other impervious cover together, so it is the binding limit on how much of the lot can be developed.
- The 200 ft lot width is a minimum road frontage; this district states no average lot width.
- The 1,500 sq ft minimum is a floor area for the building, not a livable first-floor area for dwelling purposes.
- Accessory structures have their own yard requirements, 40 ft front, 20 ft side and 30 ft rear, separate from the principal building setbacks shown.
- The 65 ft front yard is the deepest in Patterson.
Commercial Recreation - The 25% coverage figure is a maximum impervious surface cap, counting buildings, paving and every other impervious cover together, so it is the binding site constraint. The 200 ft width figure is the minimum road frontage.
- Accessory structures have their own yard requirements, separate from the principal building setbacks: 40 ft front, 20 ft side, 30 ft rear.
- No building coverage percentage is set, so the impervious surface cap is what to model.
- No average lot width is stated for this district.
- No minimum floor area applies in this district.
Open Space Overlay District - OSO is an overlay, so the underlying residence district's standards apply alongside these figures. The minimum lot size is set by § 138-49.A in the subdivision chapter rather than in the zoning schedule.
- Two width standards both bind: an average lot width of 150 ft and a minimum road frontage of 125 ft. The figure shown is the average lot width.
- The 20% figure is a maximum impervious surface coverage, counting buildings, paving and every other impervious cover together.
- Accessory structures have their own yard requirements, separate from the principal building setbacks shown: 35 ft front, 20 ft side, 30 ft rear.
- The open space restrictions of Chapter 138, Part 2 apply on top of these standards.
- The 1,000 sq ft minimum is livable first floor area for dwelling purposes.
Size limits on record in Patterson
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 Patterson:
- Putnam Lake ResidenceFloor area must be greater than 400 square feet and less than 600 square feet, and no more than 35% of the combined livable floor area.
- Residence 1Floor area must be greater than 400 square feet and less than 600 square feet, and no more than 35% of the combined livable floor area.
- Residence 2Floor area must be greater than 400 square feet and less than 600 square feet, and no more than 35% of the combined livable floor area.
- Residence 4Floor area must be greater than 400 square feet and less than 600 square feet, and no more than 35% of the combined livable floor area.
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. Renting a home here requires a permit. Chapter 129, the rental registration law, requires a permit for every rental dwelling unit under § 129-4, and there is no minimum-stay exclusion, so short stays are covered. Separate question from whether you can build the unit.
- Zoning codewww.pattersonny.org/ZoningRegs/AdoptedSchedule.pdf
- Building dept(845) 878-6500
Sizing up a specific parcel in Patterson?
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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 $13,580 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: the Offsite / Aldo cost engine and zoning dataset.