Henrietta · ADU cost
What it costs to build an ADU in Henrietta, NY
An 800 sq ft accessory dwelling unit in Henrietta runs roughly $200k–260k, or about $249–327/sq ft, and that per-square-foot figure sits deliberately above the $204–268/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 Henrietta maps 5 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 Henrietta
Standard finish, slab on grade, on a flat and clear part of the lot, general-contractor margin included. These are structure costs at Monroe County pricing, before the service and septic work a second dwelling can trigger.
| Size | Type | $ / sq ft | Estimated total |
|---|---|---|---|
| 400 sq ft | Studio | $331–$433 | $130k–175k |
| 600 sq ft | One bedroom | $276–$362 | $165k–215k |
| 800 sq ft | One bedroom, larger | $249–$327 | $200k–260k |
| 1,000 sq ft | Two bedroom | $233–$305 | $235k–305k |
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 | $28–$34 | $16 | 55% |
| Electrical | $18–$24 | $13 | 35% |
| HVAC | $23–$28 | $15 | 45% |
| Insulation | $7–$9 | $7 | — |
| Interior finishes | $32–$43 | $27 | 15% |
| Millwork & cabinetry | $18–$28 | $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 Henrietta 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 |
|---|---|---|---|---|
| R-1-20 Residential | 0.46 ac | 60 / 8 / 10 ft | — | No |
| R-1-15 Residential | 0.34 ac | 40 / 8 / 10 ft | — | No |
| R-2-15 Residential | 0.28 ac | 40 / 8 / 10 ft | — | No |
| Rural Residential — served by municipal water and sewer | 2 ac | 30 / 10 / 30 ft | — | No |
| Rural Residential — not served by both municipal water and sewer | 5 ac | 40 / 10 / 40 ft | — | No |
R-1-20 Residential - The 1,400 sq ft minimum applies to a one-storey ranch or Raised Ranch B; a two-storey house must total 2,000 sq ft, with at least 1,000 on the first floor and 600 on the second. The 25% coverage cap counts principal and accessory buildings together.
- A Raised Ranch A, a one-and-a-half-storey house or a Split-Level A must be at least 1,200 sq ft under § 295-11.
- Garages, porches and areaways are excluded when the minimum building size is measured.
- Height is capped at two stories of any kind above the basement, with a separate 21 ft limit measured from the top of the first floor of the first story to the ceiling of the second story (§ 295-8).
- Accessory buildings other than garages may cover no more than 1% of the lot in total, and no more than two individual accessory buildings are permitted.
- In a subdivision, the Planning Board requires enough variation in dwelling types, exterior architecture or floor plans to avoid a uniform or monotonous appearance.
R-1-15 Residential - Height is capped at two stories above the basement, and separately at 21 ft measured inside, from the top of the first floor to the ceiling of the second story, rather than from grade to ridge (§ 295-8).
- The story count, rather than the 21 ft figure, is the height standard that binds.
- The 25% building coverage cap counts the house and accessory buildings together.
- Accessory buildings other than garages may cover no more than 1% of the lot in total, and no more than two individual accessory buildings are allowed.
- Minimum building size varies by house type under § 295-11: 850 sq ft for a Raised Ranch A, one-and-a-half story or Split-Level A, and 1,040 sq ft for a one-story ranch or Raised Ranch B.
- A two-story house must total 1,320 sq ft, with at least 660 sq ft on the first floor and 264 sq ft on the second.
R-2-15 Residential - The figures shown apply to a single-family home. A two-family use has a separate, larger set of dimensional requirements, and this is the town's only residential district reaching a multiple dwelling.
- A two-family unit takes 15,000 sq ft and 100 ft of width against the 12,000 sq ft and 75 ft a single-family needs, a quarter more land and a third more frontage.
- A multiple dwelling is reachable by Town Board special permit at up to 12 units per acre, with 60 ft from every property line, or 30 ft beside commercial land, and 35 ft of height.
- No more than 35% of such a parcel may be built on, green space excludes slopes over 15%, and habitable area runs 500 sq ft for a studio, 600 for a one-bedroom, 800 for a two-bedroom and 950 for three.
- § 295-8 caps a residential structure at two stories of any kind above the basement and at 21 ft measured from the top of the first floor to the ceiling of the second story, an interior measurement.
- The 25% building coverage cap counts principal and accessory buildings together; accessory buildings, garages excluded, may not cover more than 1% of the lot, and no more than two are permitted.
- The 810 sq ft applies to a one-storey ranch or Raised Ranch B; a Raised Ranch A, one-and-a-half-storey or Split-Level A needs 672 sq ft, and a two-storey 960 sq ft total, 480 on the first floor.
Rural Residential — served by municipal water and sewer - The two-acre minimum applies only to a lot with both municipal water and sewer that sits outside a state-certified, county-adopted agricultural district under § 295-10.1F. A lot missing either condition falls to the five-acre tier.
- Senior housing is the only multiple-dwelling form permitted here, capped at 6 units per acre, with 60 ft from every property line, 30 ft beside commercial land, and 40 ft between buildings.
- No more than 35% of such a parcel may be built on, and habitable area runs 500 sq ft for a studio, 600 for a one-bedroom, 800 for a two-bedroom and 950 for a three-bedroom.
- Each lot must also contain at least 10,000 sq ft of contiguous area for building and yard free of wetlands, surface water and slopes over 15%, so a constrained two-acre lot can fail even at full size.
- The front setback shown is for a town or private road; a lot on a county or state road owes 50 ft. Side yards are not equal: 10 ft on one side and 15 ft on the other.
- Coverage counts principal and accessory buildings together, accessory buildings may not exceed 1% of the lot and no more than two are permitted; the lot minimum may be smaller under Article IXB.
- § 295-8 caps a residential structure at two storeys above the basement, plus 21 ft measured from the top of the first floor to the ceiling of the second storey, an interior measurement.
Rural Residential — not served by both municipal water and sewer - Each lot must contain at least 20,000 sq ft of contiguous area for building and yard, free of wetlands, surface water and slopes over 15%. A lot inside a state-certified, county-adopted agricultural district also needs five acres, even if fully serviced (§ 295-10.1F).
- Senior housing is the only multiple-dwelling form permitted here, capped at 6 units per acre by Town Board special permit, with 60 ft from every property line, or 30 ft beside commercial land.
- No more than 35% of such a parcel may be built on, and habitable area runs 500 sq ft for a studio, 600 for a one-bedroom, 800 for a two-bedroom and 950 for a three-bedroom.
- Side yards are not symmetric, 10 ft on one side and 20 ft on the other, and a lot on a county or state road owes a 60 ft front setback rather than the 40 ft shown.
- The lot minimum may be smaller under the open space incentive in Article IXB, and minimum building size follows the R-1-15 schedule: 1,040 sq ft for a one-story ranch and 1,320 sq ft for a two-story.
- Building coverage counts principal and accessory buildings together. Accessory buildings, garages excluded, may cover no more than 1% of the lot, and no more than two are permitted.
- § 295-8 also limits a residential building to 21 ft measured from the top of the first floor of the first story to the ceiling of the second story, an interior measurement, not grade to ridge.
Size limits on record in Henrietta
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 Henrietta:
- R-1-20 ResidentialA two-family dwelling in R-2-15 needs a lot of at least 15,000 sq ft under § 295-10, and the permit comes from the Town Board (Article XII and § 295-13).
- R-1-15 ResidentialA two-family dwelling in R-2-15 needs a lot of at least 15,000 sq ft under § 295-10, and the permit comes from the Town Board (Article XII and § 295-13).
- R-2-15 ResidentialA two-family dwelling in R-2-15 needs a lot of at least 15,000 sq ft under § 295-10, and the permit comes from the Town Board (Article XII and § 295-13).
- Rural Residential — served by municipal water and sewerA two-family dwelling in R-2-15 needs a lot of at least 15,000 sq ft under § 295-10, and the permit comes from the Town Board (Article XII and § 295-13).
- Rural Residential — not served by both municipal water and sewerA two-family dwelling in R-2-15 needs a lot of at least 15,000 sq ft under § 295-10, and the permit comes from the Town Board (Article XII and § 295-13).
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 RG&E 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 Henrietta has no local short-term rental law, and that is not the same as permission. Confirm with Building & Fire Prevention before counting on renting a home short term. Separate question from whether you can build the unit.
- Zoning codeecode360.com/8225074
- Building dept(585) 359-7060
Sizing up a specific parcel in Henrietta?
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 Henrietta runs $204–268/sq ft, about $370k–480k at 1,800 sq ft , plus roughly $6,408 for a conforming lot. See what it costs to build a house in Henrietta.
ADU cost in nearby towns
All Monroe County towns: Rochester (City) · Brighton · Chili · Clarkson · Gates · Greece · Hamlin · Irondequoit · Mendon · Ogden · Parma · Penfield · Perinton · Pittsford · Riga · Rush · Sweden · Webster · Wheatland · East Rochester (Village) · Brockport (Village) · Churchville (Village) · Fairport (Village) · Hilton (Village) · Honeoye Falls (Village) · Pittsford (Village) · Scottsville (Village) · Spencerport (Village) · Webster (Village)
More on Henrietta: Can you build an ADU here? · Zoning for new construction · Monroe County build cost
ADU cost in Henrietta: common questions
How much does it cost to build an ADU in Henrietta, NY?
An 800 sq ft accessory dwelling unit in Town of Henrietta runs roughly $200k–260k at a standard finish, general-contractor margin included. A 400 sq ft studio runs about $130k–175k. 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 Henrietta?
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 $249–327/sq ft against $204–268/sq ft for a full house, even though it is the same trades doing the same work.
Are ADUs allowed in Henrietta?
Town of Henrietta has 5 districts. All districts prohibit ADUs. Check the specific address with the free ADU checker or confirm with the building department at (585) 359-7060 before you spend money on design.
Can I rent an ADU in Henrietta short term?
No local short-term-rental law on record - which is not the same as permission for Town of Henrietta. 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 Monroe 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 Henrietta vary by district and often carry exceptions this page does not show; zoning last reviewed 2026-08-07; verify with the building department at (585) 359-7060 before relying on any answer. Sources: the Offsite / Aldo cost engine and zoning dataset.