Nassau · ADU cost
What it costs to build an ADU in Nassau, NY
An 800 sq ft accessory dwelling unit in Nassau runs roughly $195k–255k, or about $244–319/sq ft, and that per-square-foot figure sits deliberately above the $200–262/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 Nassau maps 4 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 Nassau
Standard finish, slab on grade, on a flat and clear part of the lot, general-contractor margin included. These are structure costs at Rensselaer County pricing, before the service and septic work a second dwelling can trigger.
| Size | Type | $ / sq ft | Estimated total |
|---|---|---|---|
| 400 sq ft | Studio | $323–$424 | $130k–170k |
| 600 sq ft | One bedroom | $270–$354 | $160k–210k |
| 800 sq ft | One bedroom, larger | $244–$319 | $195k–255k |
| 1,000 sq ft | Two bedroom | $228–$299 | $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–$22 | $16 | — |
| Framing | $25–$31 | $25 | — |
| Envelope - roof, siding, windows | $31–$40 | $31 | — |
| Plumbing | $27–$33 | $16 | 55% |
| Electrical | $18–$23 | $12 | 35% |
| HVAC | $22–$28 | $14 | 45% |
| Insulation | $7–$9 | $7 | — |
| Interior finishes | $32–$42 | $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 Nassau 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 |
|---|---|---|---|---|
| Rural Residential District | 2 ac | 75 / 50 / 75 ft | 35 ft | No |
| General Business District | 2 ac | 75 / 50 / 75 ft | 35 ft | No |
| Hamlet District | 1 ac | 25 / 25 / 25 ft | 35 ft | No |
| Waterfront Residential District | 1 ac | 50 / 50 / 50 ft | 35 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 National Grid 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 local short-term-rental law found for the Town of Nassau. The Town's code IS reachable online, contrary to what was previously assumed here: townofnassau.org publishes the full 135-page 2011 Zoning Law (adopted by the Town Board 2011-09-08) plus a complete local-law index running through Local Law #1 of 2026. Read in full 2026-08-27. No local law regulates short-term rental, transient occupancy, rental registration or rental licensing — the index runs to zoning, subdivision, solar, cannabis opt-outs, grasslands, tax exemptions, sewer use, littering, dogs and code administration. THE USE TABLE IS CLOSED AND IT HAS A TRANSIENT-HOUSING CATEGORY. Schedule B carries the note 'Any use not specifically listed below is prohibited', and the definitions reinforce it: 'PROHIBITED USE: Any use which is not listed specifically, or through similar use, as a permitted, special permit or accessory use in the District Schedule of Use Regulations shall be considered a prohibited use under this Local Law.' Under the heading HOUSING - TRANSIENT the Schedule lists five uses across the five districts (Rural-Residential, Waterfront Residential, Hamlet, General Business, Aquifer Overlay): Camp, Group home, Bed & Breakfast, Hotel and Motel. BED & BREAKFAST IS SITE PLAN APPROVAL IN ALL FIVE DISTRICTS — AND IT IS OWNER-OCCUPIED BY DEFINITION: 'An owner-occupied dwelling used for renting accommodations to transient, fee-paying guests and providing not more than one meal (breakfast) daily to lodging guests only.' Hotel is a special permit in Rural-Residential, Waterfront Residential and Hamlet, site plan approval in General Business and not permitted in the Aquifer Overlay; Motel is a special permit in Rural-Residential and Waterfront Residential and not permitted in Hamlet. Neither hotel nor motel describes a house: 'HOTEL: A building in which lodging is provided and offered to the public for compensation, and which is open to transient guests and with access to units primarily from interior lobbies, courts...'. SO A NON-OWNER-OCCUPIED WHOLE-HOUSE SHORT-TERM RENTAL HAS NO LISTED USE IN NASSAU, and the only door left open is the 'or through similar use' clause in the definition of prohibited use, which is a discretionary interpretation by the Town rather than a right. That reading has not been confirmed with the Town, so this stays a dated negative finding and not a ban. Separately, New York State's 2025 STR registry requires every host statewide to register the unit through the Rensselaer County registry regardless of what the municipality allows. Confirm with the building department at (518) 766-3044 before listing. Separate question from whether you can build the unit.
- Building dept(518) 766-3044
Sizing up a specific parcel in Nassau?
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 Nassau runs $200–262/sq ft, about $360k–470k at 1,800 sq ft , plus roughly $6,858 for a conforming lot. See what it costs to build a house in Nassau.
ADU cost in nearby towns
All Rensselaer County towns: Rensselaer (City) · Troy (City) · Berlin · Brunswick · East Greenbush · Hoosick · North Greenbush · Poestenkill · Sand Lake · Schaghticoke · Schodack · Stephentown · Castleton-on-Hudson (Village) · East Nassau (Village) · Hoosick Falls (Village) · Nassau (Village)
More on Nassau: Can you build an ADU here? · Zoning for new construction · Rensselaer County build cost
ADU cost in Nassau: common questions
How much does it cost to build an ADU in Nassau, NY?
An 800 sq ft accessory dwelling unit in Town of Nassau runs roughly $195k–255k 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 Nassau?
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 $244–319/sq ft against $200–262/sq ft for a full house, even though it is the same trades doing the same work.
Are ADUs allowed in Nassau?
Town of Nassau has 4 districts. All districts prohibit ADUs. Check the specific address with the free ADU checker or confirm with the building department at (518) 766-3044 before you spend money on design.
Can I rent an ADU in Nassau short term?
No local short-term-rental law on record - which is not the same as permission for Town of Nassau. 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 Rensselaer 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 Nassau vary by district and often carry exceptions this page does not show; zoning last reviewed 2026-08-05; verify with the building department at (518) 766-3044 before relying on any answer. Sources: Offsite / Aldo cost engine (costEngine.js + constants.js); zoning dataset (municipalData.js).