Cairo · ADU cost
What it costs to build an ADU in Cairo, NY
An 800 sq ft accessory dwelling unit in Cairo runs roughly $195k–255k, or about $241–316/sq ft, and that per-square-foot figure sits deliberately above the $197–259/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 Cairo 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 Cairo
Standard finish, slab on grade, on a flat and clear part of the lot, general-contractor margin included. These are structure costs at Greene County pricing, before the service and septic work a second dwelling can trigger.
| Size | Type | $ / sq ft | Estimated total |
|---|---|---|---|
| 400 sq ft | Studio | $320–$419 | $130k–170k |
| 600 sq ft | One bedroom | $267–$350 | $160k–210k |
| 800 sq ft | One bedroom, larger | $241–$316 | $195k–255k |
| 1,000 sq ft | Two bedroom | $225–$295 | $225k–295k |
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 | $31–$42 | $26 | 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 Cairo 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 | 2 ac | - / 25 / 25 ft | — | As of right |
| Mountain Top Residential | 2 ac | - / 25 / 25 ft | — | As of right |
| Main Street Downtown | 2 ac | - / 15 / 15 ft | — | As of right |
| Main Street Commercial | 2 ac | - / 15 / 15 ft | — | As of right |
| Hamlet Cairo | 2 ac | - / 15 / 15 ft | — | As of right |
| Commercial Mixed Use | 2 ac | - / 25 / 25 ft | — | As of right |
| Commercial/Industrial | 2 ac | - / 25 / 25 ft | — | As of right |
| Municipal | 2 ac | - / 25 / 25 ft | — | No |
| Adult Use District | 2 ac | - / 25 / 25 ft | — | — |
Rural Residential, Mountain Top Residential, Commercial Mixed Use, Commercial/Industrial, Municipal, Adult Use District - The front setback is 65 feet measured from the center of the roadway, not from the front lot line, and a lot fronting two or more roads is held to 65 feet from the center line of each of them.
- The 2 acre minimum is for land with neither municipal water nor sewer. With one of them it is 1/2 acre (0.5 acre) and with both it is 1/4 acre (0.25 acre).
- Maximum lot coverage rises to 80% where either municipal water or sewer is available.
- A lot fronting two or more roads is held to 65 feet from the center line of each of them.
- Minimum frontage on a public or private road is 150 feet in this district, and 50 feet on a flag lot or along the arc of a cul-de-sac.
- Fences, retaining walls, mailboxes, utilities, septic systems, wells, stormwater measures and driveways may stand inside a required setback.
- The zoning law sets no maximum building height in any district.
Main Street Downtown - There is no numbered front setback here. § V.C.2.a requires the front of a building to be consistent with the existing, surrounding structures, so the figure depends on the neighbours rather than on the district.
- The 2 acre minimum is for land with neither municipal water nor sewer. With one of them it is 1/2 acre (0.5 acre) and with both it is 1/4 acre (0.25 acre).
- Maximum lot coverage rises to 80% where either municipal water or sewer is available.
- The side and rear setbacks of 15 feet are measured from the property line.
- Minimum frontage on a public or private road is 25 feet in this district, and 50 feet on a flag lot or along the arc of a cul-de-sac.
- Fences, retaining walls, mailboxes, utilities, septic systems, wells, stormwater measures and driveways may stand inside a required setback.
- The zoning law sets no maximum building height in any district.
Main Street Commercial, Hamlet Cairo - There is no numbered front setback here. § V.C.2.a requires the front of a building to be consistent with the existing, surrounding structures, so the figure depends on the neighbours rather than on the district.
- The 2 acre minimum is for land with neither municipal water nor sewer. With one of them it is 1/2 acre (0.5 acre) and with both it is 1/4 acre (0.25 acre).
- Maximum lot coverage rises to 80% where either municipal water or sewer is available.
- The side and rear setbacks of 15 feet are measured from the property line.
- Minimum frontage on a public or private road is 50 feet in this district, and 50 feet on a flag lot or along the arc of a cul-de-sac.
- Fences, retaining walls, mailboxes, utilities, septic systems, wells, stormwater measures and driveways may stand inside a required setback.
- The zoning law sets no maximum building height in any district.
Size limits on record in Cairo
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 Cairo:
- Rural ResidentialA guest cottage is capped at 50% of the house's square footage and may not be rented, and a lot cannot have both a guest cottage and an accessory apartment.
- Mountain Top ResidentialA guest cottage is capped at 50% of the house's square footage and may not be rented, and a lot cannot have both a guest cottage and an accessory apartment.
- Main Street DowntownA guest cottage is capped at 50% of the house's square footage and may not be rented, and a lot cannot have both a guest cottage and an accessory apartment.
- Main Street CommercialA guest cottage is capped at 50% of the house's square footage and may not be rented, and a lot cannot have both a guest cottage and an accessory apartment.
- Hamlet CairoA guest cottage is capped at 50% of the house's square footage and may not be rented, and a lot cannot have both a guest cottage and an accessory apartment.
- Commercial Mixed UseA guest cottage is capped at 50% of the house's square footage and may not be rented, and a lot cannot have both a guest cottage and an accessory apartment.
- Commercial/IndustrialA guest cottage is capped at 50% of the house's square footage and may not be rented, and a lot cannot have both a guest cottage and an accessory apartment.
- MunicipalA guest cottage is capped at 50% of the house's square footage and may not be rented, and a lot cannot have both a guest cottage and an accessory apartment.
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. The Town of Cairo has no local short-term rental law. That is not the same as permission, so confirm with the town before counting on rental income. Separate question from whether you can build the unit.
- Zoning codetownofcairo.com/wp-content/uploads/2015/12/2017-Zoning-Laws-Updated.pdf
- Building dept(518) 622-3120
Sizing up a specific parcel in Cairo?
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 Cairo runs $197–259/sq ft, about $355k–465k at 1,800 sq ft , plus roughly $25,578 for a conforming lot. See what it costs to build a house in Cairo.
ADU cost in nearby towns
All Greene County towns: Athens · Catskill · Coxsackie · Greenville · Halcott · Jewett · Lexington · New Baltimore · Athens (Village) · Catskill (Village) · Coxsackie (Village) · Hunter (Village) · Tannersville (Village)
More on Cairo: Can you build an ADU here? · Zoning for new construction · Greene County build cost
ADU cost in Cairo: common questions
How much does it cost to build an ADU in Cairo, NY?
An 800 sq ft accessory dwelling unit in Town of Cairo 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 Cairo?
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 $241–316/sq ft against $197–259/sq ft for a full house, even though it is the same trades doing the same work.
Are ADUs allowed in Cairo?
Town of Cairo has 9 districts. 7 districts allow ADUs, 1 does not. 1 district has incomplete data - verify with the building department at (518) 622-3120. Check the specific address with the free ADU checker before you spend money on design.
Can I rent an ADU in Cairo short term?
No local short-term-rental law on record - which is not the same as permission for Town of Cairo. 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 Greene 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 Cairo vary by district and often carry exceptions this page does not show; zoning last reviewed 2026-10-05; verify with the building department at (518) 622-3120 before relying on any answer. Sources: the Offsite / Aldo cost engine and zoning dataset.