Green Island · ADU cost
What it costs to build an ADU in Green Island, NY
An 800 sq ft accessory dwelling unit in Green Island 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 Green Island maps 6 districts that treat accessory units differently from one another, so read the table below as a starting point rather than a verdict.
Check a specific parcel for an ADU in Aldo, free →
ADU cost by size in Green Island
Standard finish, slab on grade, on a flat and clear part of the lot, general-contractor margin included. These are structure costs at Albany 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 Green Island 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 |
|---|---|---|---|---|
| Commercial | 0.069 ac | 13 / 3 / 15 ft | 35 ft | No |
| Industrial | 0.46 ac | 40 / 50 / 50 ft | 35 ft | No |
| Planned Development | — | — | — | — |
| Residential 1 | 0.069 ac | 13 / 3 / 15 ft | 35 ft | No |
| Residential 2 | 0.069 ac | 13 / 3 / 15 ft | 35 ft | No |
| Recreational | — | — | — | No |
Commercial - A home is allowed here on the same figures as the R2 district: 1,500 sq ft of land per unit for a one- or two-family, and 1,000 sq ft per unit for a multiple-family building.
- The side yard is a pair: 3 ft on one side and 5 ft for the two combined.
- The 3,000 sq ft lot minimum has a floor beneath it for an existing undersized lot, an absolute minimum of 2,000 square feet.
- A gasoline station breaks the pattern entirely: 20,000 sq ft on a 150 ft by 125 ft lot, with 30 ft front, 30 ft one side, 60 ft both sides and 30 ft rear, and no coverage maximum at all (§ 169-25).
Industrial - The 50 ft side and rear yards carry a footnote saying the yard sizes apply when abutting a residential district, and the schedule prints no other figure for a lot that abuts none, so whether 50 ft is the general requirement or only the abutting one is unsettled.
- One row in the schedule covers every industrial use here.
Planned Development - There are no published dimensions for a planned development district. The standards come from the plan approved for that particular development.
Residential 1 - A two-family house needs the same lot as a one-family: one row covers both, at 3,000 sq ft of lot and 1,500 sq ft of land per dwelling unit.
- The 3,000 sq ft lot minimum carries a footnote setting an absolute minimum of 2,000 sq ft, so an existing undersized lot has a floor below the district figure.
- Multiple-family is not a listed use in this district.
- Nonresidential use shares every figure here, differing only in having no land-per-unit rate.
Residential 2 - One- and two-family share the base row at 1,500 sq ft of land per dwelling unit, and a multiple-family building drops to 1,000 sq ft per unit on the same 3,000 sq ft lot.
- The 3,000 sq ft lot minimum carries a footnote setting an absolute minimum of 2,000 sq ft, so an existing undersized lot has a floor below the district figure.
- Nonresidential use shares the same figures, with no land-per-unit rate.
Recreational - The village's area and bulk schedule publishes no row for this district, so its dimensional standards are not published there.
- Public utilities are listed with no figures and referred instead to § 169-26.
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 Green Island Power Authority 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. The village has no local short-term rental law. That is not the same as permission, so check with the village office before counting on a short-term rental here. Separate question from whether you can build the unit.
- Zoning codeecode360.com/GR1167
- Building dept(518) 629-0368
Sizing up a specific parcel in Green Island?
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 Green Island runs $202–265/sq ft, about $365k–475k at 1,800 sq ft , plus roughly $38,775 for a conforming lot. See what it costs to build a house in Green Island.
ADU cost in nearby towns
All Albany County towns: Albany (City) · Cohoes (City) · Watervliet (City) · Berne · Bethlehem · Coeymans · Colonie · Guilderland · Knox · New Scotland · Rensselaerville · Westerlo · Altamont (Village) · Colonie (Village) · Menands (Village) · Ravena (Village) · Voorheesville (Village)
More on Green Island: Can you build an ADU here? · Zoning for new construction · Albany County build cost
ADU cost in Green Island: common questions
How much does it cost to build an ADU in Green Island, NY?
An 800 sq ft accessory dwelling unit in Village of Green Island 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 Green Island?
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 Green Island?
Village of Green Island has 6 districts. 5 of 6 districts prohibit ADUs. 1 district has incomplete data - verify with the building department at (518) 629-0368. Check the specific address with the free ADU checker before you spend money on design.
Can I rent an ADU in Green Island short term?
No local short-term-rental law on record - which is not the same as permission for Village of Green Island. 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 Albany 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 Green Island vary by district and often carry exceptions this page does not show; zoning last reviewed 2026-09-19; verify with the building department at (518) 629-0368 before relying on any answer. Sources: the Offsite / Aldo cost engine and zoning dataset.