Chatham · ADU cost
What it costs to build an ADU in Chatham, NY
An 800 sq ft accessory dwelling unit in Chatham runs roughly $195k–260k, or about $247–323/sq ft, and that per-square-foot figure sits deliberately above the $202–265/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 Chatham maps 6 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 Chatham
Standard finish, slab on grade, on a flat and clear part of the lot, general-contractor margin included. These are structure costs at Columbia County pricing, before the service and septic work a second dwelling can trigger.
| Size | Type | $ / sq ft | Estimated total |
|---|---|---|---|
| 400 sq ft | Studio | $327–$428 | $130k–170k |
| 600 sq ft | One bedroom | $273–$358 | $165k–215k |
| 800 sq ft | One bedroom, larger | $247–$323 | $195k–260k |
| 1,000 sq ft | Two bedroom | $231–$302 | $230k–300k |
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 | $7–$11 | $7 | — |
| Foundation | $16–$23 | $16 | — |
| Framing | $25–$32 | $25 | — |
| Envelope - roof, siding, windows | $32–$41 | $32 | — |
| Plumbing | $27–$33 | $16 | 55% |
| Electrical | $18–$23 | $13 | 35% |
| HVAC | $23–$28 | $14 | 45% |
| Insulation | $7–$9 | $7 | — |
| Interior finishes | $32–$43 | $27 | 15% |
| Millwork & cabinetry | $18–$27 | $11 | 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 Chatham 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 |
|---|---|---|---|---|
| Residential (1- & 2-family) | 0.17 ac | 30 / 15 / 30 ft | 35 ft | Special permit |
| Suburban Residential | 0.34 ac | 30 / 20 / 50 ft | 35 ft | Special permit |
| Commercial 1 | — | 0 / 0 / 30 ft | 40 ft | No |
| Commercial 2 (Church-Coleman) | 0.17 ac | 30 / 15 / 30 ft | 35 ft | Special permit |
| Commercial 3 (Southern Gateway) | 0.46 ac | 30 / 20 / 50 ft | 35 ft | No |
| Industrial | 0.92 ac | 50 / 30 / 30 ft | 35 ft | No |
Residential (1- & 2-family) — The base row is the 1- AND 2-FAMILY DWELLING case: 7,500 sq ft for the first unit PLUS 2,500 sq ft for the second, which is why the lot figure is the first-unit minimum. A nonresidential use takes 10,000 sq ft on a 75 ft lot. Minimum 1 storey, maximum 2 1/2 and 35 ft. THE RESIDENTIAL COVERAGE LIMIT IS A FORMULA, NOT A PERCENTAGE, and it is the same in EVERY district: maximum lot coverage for residential uses including associated accessory uses is 2,400 sq ft PLUS 25% of the lot area up to 3 acres PLUS 5% of the lot area beyond 3 acres. The percentage recorded above is the NONRESIDENTIAL figure, which is the only one this field can hold. The schedule sets a MINIMUM number of storeys as well as a maximum — a floor on building height, which is unusual and has no field. The Historic Overzone (HO) applies the density regulations of the underlying district, so it adds no figures of its own. See § 110-47 for existing undersized lots and § 110-24 for accessory structures and uses. Minimum 1 storey(s), maximum 2 1/2 and 35 ft. Nonresidential minimum lot width 75 ft.
Suburban Residential — The base row is the 1- AND 2-FAMILY DWELLING case: 15,000 sq ft for the first unit PLUS 5,000 sq ft for the second. A nonresidential use takes 20,000 sq ft on a 100 ft lot. THE RESIDENTIAL COVERAGE LIMIT IS A FORMULA, NOT A PERCENTAGE, and it is the same in EVERY district: maximum lot coverage for residential uses including associated accessory uses is 2,400 sq ft PLUS 25% of the lot area up to 3 acres PLUS 5% of the lot area beyond 3 acres. The percentage recorded above is the NONRESIDENTIAL figure, which is the only one this field can hold. The schedule sets a MINIMUM number of storeys as well as a maximum — a floor on building height, which is unusual and has no field. The Historic Overzone (HO) applies the density regulations of the underlying district, so it adds no figures of its own. See § 110-47 for existing undersized lots and § 110-24 for accessory structures and uses. Minimum 2 storey(s), maximum 2 1/2 and 35 ft. Nonresidential minimum lot width 100 ft.
Commercial 1 — C-1 PUBLISHES ALMOST NO LOT STANDARD: the schedule prints "N.R." — not required — for the residential and nonresidential minimum lot area AND for both lot widths. Its front yard is a RANGE of 0 to 10 ft residential and 0 to 0 ft nonresidential, and no coverage percentage is required. Note 1: the front yard shall be reduced or enlarged to conform to neighbourhood conditions. THE RESIDENTIAL COVERAGE LIMIT IS A FORMULA, NOT A PERCENTAGE, and it is the same in EVERY district: maximum lot coverage for residential uses including associated accessory uses is 2,400 sq ft PLUS 25% of the lot area up to 3 acres PLUS 5% of the lot area beyond 3 acres. The percentage recorded above is the NONRESIDENTIAL figure, which is the only one this field can hold. The schedule sets a MINIMUM number of storeys as well as a maximum — a floor on building height, which is unusual and has no field. The Historic Overzone (HO) applies the density regulations of the underlying district, so it adds no figures of its own. See § 110-47 for existing undersized lots and § 110-24 for accessory structures and uses. Minimum 2 storey(s), maximum 3 and 40 ft.
Commercial 2 (Church-Coleman) — C-2 is the Church-Coleman district. The base row is the residential case: 7,500 sq ft for the first unit PLUS 2,500 for the second. A nonresidential use takes 15,000 sq ft on a 75 ft lot. THE RESIDENTIAL COVERAGE LIMIT IS A FORMULA, NOT A PERCENTAGE, and it is the same in EVERY district: maximum lot coverage for residential uses including associated accessory uses is 2,400 sq ft PLUS 25% of the lot area up to 3 acres PLUS 5% of the lot area beyond 3 acres. The percentage recorded above is the NONRESIDENTIAL figure, which is the only one this field can hold. The schedule sets a MINIMUM number of storeys as well as a maximum — a floor on building height, which is unusual and has no field. The Historic Overzone (HO) applies the density regulations of the underlying district, so it adds no figures of its own. See § 110-47 for existing undersized lots and § 110-24 for accessory structures and uses. Minimum 2 storey(s), maximum 2 1/2 and 35 ft. Nonresidential minimum lot width 75 ft.
Commercial 3 (Southern Gateway) — C-3 is the Southern Gateway district. The schedule prints N.A. for a one- or two-family residential lot — the base row is the NONRESIDENTIAL standard of 20,000 sq ft, and the 100 ft width recorded above is that row's. Note #: more than one business may be allowed per lot, the number fixed when the special use permit issues, and the Planning Board may modify the side-yard setback for a multiple-use site. THE RESIDENTIAL COVERAGE LIMIT IS A FORMULA, NOT A PERCENTAGE, and it is the same in EVERY district: maximum lot coverage for residential uses including associated accessory uses is 2,400 sq ft PLUS 25% of the lot area up to 3 acres PLUS 5% of the lot area beyond 3 acres. The percentage recorded above is the NONRESIDENTIAL figure, which is the only one this field can hold. The schedule sets a MINIMUM number of storeys as well as a maximum — a floor on building height, which is unusual and has no field. The Historic Overzone (HO) applies the density regulations of the underlying district, so it adds no figures of its own. See § 110-47 for existing undersized lots and § 110-24 for accessory structures and uses. Minimum 2 storey(s), maximum 2 1/2 and 35 ft.
Industrial — The Industrial district's figures are nonresidential. THE RESIDENTIAL COVERAGE LIMIT IS A FORMULA, NOT A PERCENTAGE, and it is the same in EVERY district: maximum lot coverage for residential uses including associated accessory uses is 2,400 sq ft PLUS 25% of the lot area up to 3 acres PLUS 5% of the lot area beyond 3 acres. The percentage recorded above is the NONRESIDENTIAL figure, which is the only one this field can hold. The schedule sets a MINIMUM number of storeys as well as a maximum — a floor on building height, which is unusual and has no field. The Historic Overzone (HO) applies the density regulations of the underlying district, so it adds no figures of its own. See § 110-47 for existing undersized lots and § 110-24 for accessory structures and uses. Minimum 2 storey(s), maximum 3 and 40 ft.
Size limits on record in Chatham
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 Chatham:
- Commercial 2 (Church-Coleman)On a lot smaller than the acreage the district requires for two dwellings, the unit is capped at 700 sq ft
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 Central Hudson 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 rentalsNo local short-term-rental law on record - which is not the same as permission. No Village of Chatham STR ordinance found as of Jun 2026. The surrounding Town of Chatham has its own STR law (LL No. 6 of 2023) that does not apply within village boundaries. Village has a general rental property registration chapter only. Separate question from whether you can build the unit.
- Zoning codeecode360.com/29136282
- Building dept(518) 392-5821
Sizing up a specific parcel in Chatham?
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 Chatham runs $202–265/sq ft, about $365k–475k at 1,800 sq ft , plus roughly $14,026 for a conforming lot. See what it costs to build a house in Chatham.
ADU cost in nearby towns
All Columbia County towns: Hudson (City) · Ancram · Austerlitz · Canaan · Chatham · Claverack · Clermont · Copake · Gallatin · Germantown · Ghent · Hillsdale · Kinderhook · Livingston · New Lebanon · Stockport · Stuyvesant · Taghkanic · Kinderhook (Village) · Philmont (Village) · Valatie (Village)
More on Chatham: Can you build an ADU here? · Zoning for new construction · Columbia County build cost
ADU cost in Chatham: common questions
How much does it cost to build an ADU in Chatham, NY?
An 800 sq ft accessory dwelling unit in Village of Chatham runs roughly $195k–260k at a standard finish, general-contractor margin included. A 400 sq ft studio runs about $130k–170k. 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 Chatham?
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 $247–323/sq ft against $202–265/sq ft for a full house, even though it is the same trades doing the same work.
Are ADUs allowed in Chatham?
Village of Chatham has 6 districts. 3 districts prohibit ADUs, 3 require a special-use permit. Check the specific address with the free ADU checker or confirm with the building department at (518) 392-5821 before you spend money on design.
Can I rent an ADU in Chatham short term?
No local short-term-rental law on record - which is not the same as permission for Village of Chatham. 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 Columbia 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 Chatham vary by district and often carry exceptions this page does not show; zoning last reviewed 2026-06-02; verify with the building department at (518) 392-5821 before relying on any answer. Sources: Offsite / Aldo cost engine (costEngine.js + constants.js); zoning dataset (municipalData.js).