Rochester · ADU cost
What it costs to build an ADU in Rochester, NY
An 800 sq ft accessory dwelling unit in Rochester 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 city 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 City of Rochester maps 7 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 Rochester
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 Rochester 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 |
|---|---|---|---|---|
| Low-Density Residential (R-1) — 5,000 square feet of lot per detached dwelling, 20 ft front, 5 ft side (with both side yards totalling at least 15 ft), 20 ft rear, 2 1/2 stories not to exceed 35 ft, 50% maximum lot coverage. THIS IS A CITY DISTRICT AND ITS FRONTAGE AND FRONT SETBACK ARE CONTEXTUAL, NOT FIXED. Minimum lot frontage is stated as "the average frontage of lots on the block on which the property is located" — there is no number, so minLotWidthFt is null by design and a frontage answer requires measuring the block. The front setback runs a three-step cascade: the average front yard depth of buildings on the two adjoining lots, or failing that the average on the block frontage, or failing that 20 feet. The recorded 20 ft is the floor that applies when there is no built context; on a normal infill lot in a built-up block the block average governs and can be well over 20 ft. There is also a MAXIMUM front yard setback pinned to the same block average, so a Rochester house is held to the street line as well as off it — the district is contextual in both directions. Single-family ATTACHED dwellings are permitted by right at 3,000 sf of lot and 30 ft of frontage per unit, so a duplex-form building is a by-right use in the city's lowest-density residential district. A MAXIMUM BUILDING COVERAGE standard formerly sat beside the lot coverage figure and was REPEALED 9-19-2017 by Ord. No. 2017-299; the 50% recorded here is the surviving maximum LOT coverage, and the editor's note renumbering the subsections is the only trace of the repeal. | 0.1148 ac | 20 / 5 / 20 ft | 35 ft | No |
| Medium-Density Residential (R-2) — dimensionally IDENTICAL to R-1 on every recorded field: 5,000 sf minimum lot area, contextual frontage, 20 ft front setback floor, 5 ft side (15 ft combined), 2 1/2 stories not to exceed 35 ft, 50% maximum lot coverage. That identity is real, not a copy-paste error, and it is the single most useful fact about Rochester's residential zoning: the step from low to medium density buys NO extra lot area, width, height or coverage — what changes is the USE list. R-2 adds two-family dwellings by right on the same 5,000 sf lot that R-1 requires for one detached house. THE ONE DIMENSIONAL DIFFERENCE IS THE REAR YARD AND IT CUTS THE OTHER WAY: R-2's rear setback is 20 feet OR the existing setback, but in no case less than 10 feet, so an existing nonconforming rear yard is legitimised down to a 10 ft floor — a concession R-1 does not grant. The recorded 20 is the standard case. Everything said about R-1's contextual frontage and three-step front-setback cascade applies here unchanged. | 0.1148 ac | 20 / 5 / 20 ft | 35 ft | No |
| High-Density Residential (R-3) — 5,000 sf minimum lot area and 50% maximum lot coverage, the same as R-1 and R-2, but with a stated 40 ft minimum lot frontage instead of the contextual block average, 20 ft front setback floor and 5 ft side (15 ft combined). MULTIFAMILY DWELLINGS ARE PERMITTED BY RIGHT HERE, along with two-family, single-family attached, live-work space and bed-and-breakfast establishments — no special permit for any of them. HEIGHT IS A FORMULA, NOT A NUMBER, AND IT IS THE MOST IMPORTANT FIGURE IN THIS DISTRICT: maximum building height for a principal structure is TWO TIMES THE WIDTH OF THE LOT FRONTAGE. maxHeight is therefore null by design and must be computed per parcel — at the 40 ft minimum frontage the cap is 80 ft, roughly seven storeys, while a narrow 25 ft infill lot is held to 50 ft. Do not substitute the 35 ft figure from R-1 and R-2. THE REAR YARD IS ALSO A FORMULA: one third of the building height or 20 feet, whichever is GREATER, so the rear setback grows with the building and the recorded 20 is only the floor for structures up to 60 ft. On a tall R-3 building the height formula and the rear-yard formula bind against each other, and that interaction, not the lot area, is what sets the achievable envelope. | 0.1148 ac | 20 / 5 / 20 ft | — | No |
| Neighborhood Center District (C-1) — a genuinely FORM-BASED district, and its nulls are the code, not a gap. There is NO minimum lot area, NO minimum lot frontage and NO maximum lot coverage. Side and rear yards are ZERO FEET unless the lot adjoins a residential district, in which case each takes the adjacent residential district's own requirement — the recorded zeros mean zero required, not unknown. THE FRONT YARD IS A MAXIMUM, NOT A MINIMUM: buildings must sit 0 to 5 feet from the line, or at the average front yard depth of buildings along the corridor within the commercial district, so C-1 pushes the building TO the street rather than back from it, and frontSetback is null because no minimum exists to record. HEIGHT IS REGULATED FROM THE BOTTOM: C-1 sets a MINIMUM building height of two storeys or 20 feet for principal structures and NO MAXIMUM at all — the only cap on a C-1 building is the separate O-LH Overlay Limited-Height District (Article XVA, § 120-118.5), which limits principal structures to THREE STOREYS on the C-1 land and adjoining areas it is mapped over and otherwise defers entirely to the underlying district. Detached accessory structures are capped at 15 ft. | — | - / 0 / 0 ft | — | No |
| Community Center District (C-2) — the one commercial district in Rochester that states a residential lot minimum: 2,600 square feet per attached single-family unit with 30 feet of frontage per unit, which is the smallest recorded residential lot anywhere in Monroe County and roughly half of what the R districts require. No maximum lot coverage is set. Side and rear yards are N/A for principal structures, so sideSetback and rearSetback are null rather than zero — the code declines to state a standard rather than setting one at zero, which is the distinction from C-1 and C-3. THE FRONT SETBACK IS PURELY CONTEXTUAL WITH NO NUMERIC FALLBACK: the average front yard depth of buildings on the block, but in no case more than 5 feet larger than the average of the two adjoining lots. Unlike the R districts there is no "or 20 feet" backstop, so frontSetback is null and cannot be answered without surveying the block. An attached garage or carport must sit at the principal structure's front yard depth PLUS 10 feet. Like C-1, C-2 sets a MINIMUM building height — 20 feet for a principal structure — and no maximum; detached accessory structures are capped at 20 ft. | 0.0597 ac | — | — | No |
| Regional Destination Center District (C-3) — the least dimensionally constrained commercial district recorded here. No minimum lot area, no minimum lot frontage, no minimum front yard, no maximum lot coverage, no minimum building height and NO MAXIMUM BUILDING HEIGHT for principal structures. The only stated standards are the side and rear yards, both ZERO FEET unless the lot adjoins a residential district, in which case each takes the adjacent residential district's requirement — so the entire dimensional envelope of a C-3 parcel is set by what sits next door. Those recorded zeros are real values meaning zero required. A C-3 project is governed by the City-Wide Design Guidelines of Article XIX and by site plan review rather than by bulk standards, and any C-3 answer that quotes a lot size or height limit is wrong. | — | - / 0 / 0 ft | — | No |
| Open Space District (O-S) — § 120-92 sets exactly one numeric standard and declares every other one N/A: minimum lot frontage N/A, minimum lot area N/A, maximum lot coverage N/A, side and rear yards N/A unless the lot adjoins a residential district, in which case each takes that district's required setback. THE FRONT SETBACK IS THE SINGLE RECORDABLE FIGURE AND IT IS CONDITIONAL: the average front yard depth of buildings along the block, OR 35 FEET IF NO BUILDINGS STAND WITHIN 500 FEET of the proposed building. The recorded 35 is that isolated-site case, which is the normal condition in an open-space parcel and therefore the figure most likely to apply, but on a block with neighbouring buildings the average governs instead. The nulls here are the code's own N/As, not missing research. Note that a former maximum BUILDING coverage standard was repealed 9-19-2017 by Ord. No. 2017-299 and the surviving lot coverage line reads N/A, so O-S caps building footprint by nothing at all. | — | 35 / - / - ft | — | No |
Size limits on record in Rochester
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 Rochester:
- Low-Density Residential (R-1) — 5,000 square feet of lot per detached dwelling, 20 ft front, 5 ft side (with both side yards totalling at least 15 ft), 20 ft rear, 2 1/2 stories not to exceed 35 ft, 50% maximum lot coverage. THIS IS A CITY DISTRICT AND ITS FRONTAGE AND FRONT SETBACK ARE CONTEXTUAL, NOT FIXED. Minimum lot frontage is stated as "the average frontage of lots on the block on which the property is located" — there is no number, so minLotWidthFt is null by design and a frontage answer requires measuring the block. The front setback runs a three-step cascade: the average front yard depth of buildings on the two adjoining lots, or failing that the average on the block frontage, or failing that 20 feet. The recorded 20 ft is the floor that applies when there is no built context; on a normal infill lot in a built-up block the block average governs and can be well over 20 ft. There is also a MAXIMUM front yard setback pinned to the same block average, so a Rochester house is held to the street line as well as off it — the district is contextual in both directions. Single-family ATTACHED dwellings are permitted by right at 3,000 sf of lot and 30 ft of frontage per unit, so a duplex-form building is a by-right use in the city's lowest-density residential district. A MAXIMUM BUILDING COVERAGE standard formerly sat beside the lot coverage figure and was REPEALED 9-19-2017 by Ord. No. 2017-299; the 50% recorded here is the surviving maximum LOT coverage, and the editor's note renumbering the subsections is the only trace of the repeal.R-1 permits single-family ATTACHED dwellings by right alongside detached, at 3,000 sq ft of lot per unit
- Medium-Density Residential (R-2) — dimensionally IDENTICAL to R-1 on every recorded field: 5,000 sf minimum lot area, contextual frontage, 20 ft front setback floor, 5 ft side (15 ft combined), 2 1/2 stories not to exceed 35 ft, 50% maximum lot coverage. That identity is real, not a copy-paste error, and it is the single most useful fact about Rochester's residential zoning: the step from low to medium density buys NO extra lot area, width, height or coverage — what changes is the USE list. R-2 adds two-family dwellings by right on the same 5,000 sf lot that R-1 requires for one detached house. THE ONE DIMENSIONAL DIFFERENCE IS THE REAR YARD AND IT CUTS THE OTHER WAY: R-2's rear setback is 20 feet OR the existing setback, but in no case less than 10 feet, so an existing nonconforming rear yard is legitimised down to a 10 ft floor — a concession R-1 does not grant. The recorded 20 is the standard case. Everything said about R-1's contextual frontage and three-step front-setback cascade applies here unchanged.R-1 permits single-family ATTACHED dwellings by right alongside detached, at 3,000 sq ft of lot per unit
- High-Density Residential (R-3) — 5,000 sf minimum lot area and 50% maximum lot coverage, the same as R-1 and R-2, but with a stated 40 ft minimum lot frontage instead of the contextual block average, 20 ft front setback floor and 5 ft side (15 ft combined). MULTIFAMILY DWELLINGS ARE PERMITTED BY RIGHT HERE, along with two-family, single-family attached, live-work space and bed-and-breakfast establishments — no special permit for any of them. HEIGHT IS A FORMULA, NOT A NUMBER, AND IT IS THE MOST IMPORTANT FIGURE IN THIS DISTRICT: maximum building height for a principal structure is TWO TIMES THE WIDTH OF THE LOT FRONTAGE. maxHeight is therefore null by design and must be computed per parcel — at the 40 ft minimum frontage the cap is 80 ft, roughly seven storeys, while a narrow 25 ft infill lot is held to 50 ft. Do not substitute the 35 ft figure from R-1 and R-2. THE REAR YARD IS ALSO A FORMULA: one third of the building height or 20 feet, whichever is GREATER, so the rear setback grows with the building and the recorded 20 is only the floor for structures up to 60 ft. On a tall R-3 building the height formula and the rear-yard formula bind against each other, and that interaction, not the lot area, is what sets the achievable envelope.R-1 permits single-family ATTACHED dwellings by right alongside detached, at 3,000 sq ft of lot per unit
- Neighborhood Center District (C-1) — a genuinely FORM-BASED district, and its nulls are the code, not a gap. There is NO minimum lot area, NO minimum lot frontage and NO maximum lot coverage. Side and rear yards are ZERO FEET unless the lot adjoins a residential district, in which case each takes the adjacent residential district's own requirement — the recorded zeros mean zero required, not unknown. THE FRONT YARD IS A MAXIMUM, NOT A MINIMUM: buildings must sit 0 to 5 feet from the line, or at the average front yard depth of buildings along the corridor within the commercial district, so C-1 pushes the building TO the street rather than back from it, and frontSetback is null because no minimum exists to record. HEIGHT IS REGULATED FROM THE BOTTOM: C-1 sets a MINIMUM building height of two storeys or 20 feet for principal structures and NO MAXIMUM at all — the only cap on a C-1 building is the separate O-LH Overlay Limited-Height District (Article XVA, § 120-118.5), which limits principal structures to THREE STOREYS on the C-1 land and adjoining areas it is mapped over and otherwise defers entirely to the underlying district. Detached accessory structures are capped at 15 ft.R-1 permits single-family ATTACHED dwellings by right alongside detached, at 3,000 sq ft of lot per unit
- Community Center District (C-2) — the one commercial district in Rochester that states a residential lot minimum: 2,600 square feet per attached single-family unit with 30 feet of frontage per unit, which is the smallest recorded residential lot anywhere in Monroe County and roughly half of what the R districts require. No maximum lot coverage is set. Side and rear yards are N/A for principal structures, so sideSetback and rearSetback are null rather than zero — the code declines to state a standard rather than setting one at zero, which is the distinction from C-1 and C-3. THE FRONT SETBACK IS PURELY CONTEXTUAL WITH NO NUMERIC FALLBACK: the average front yard depth of buildings on the block, but in no case more than 5 feet larger than the average of the two adjoining lots. Unlike the R districts there is no "or 20 feet" backstop, so frontSetback is null and cannot be answered without surveying the block. An attached garage or carport must sit at the principal structure's front yard depth PLUS 10 feet. Like C-1, C-2 sets a MINIMUM building height — 20 feet for a principal structure — and no maximum; detached accessory structures are capped at 20 ft.R-1 permits single-family ATTACHED dwellings by right alongside detached, at 3,000 sq ft of lot per unit
- Regional Destination Center District (C-3) — the least dimensionally constrained commercial district recorded here. No minimum lot area, no minimum lot frontage, no minimum front yard, no maximum lot coverage, no minimum building height and NO MAXIMUM BUILDING HEIGHT for principal structures. The only stated standards are the side and rear yards, both ZERO FEET unless the lot adjoins a residential district, in which case each takes the adjacent residential district's requirement — so the entire dimensional envelope of a C-3 parcel is set by what sits next door. Those recorded zeros are real values meaning zero required. A C-3 project is governed by the City-Wide Design Guidelines of Article XIX and by site plan review rather than by bulk standards, and any C-3 answer that quotes a lot size or height limit is wrong.R-1 permits single-family ATTACHED dwellings by right alongside detached, at 3,000 sq ft of lot per unit
- Open Space District (O-S) — § 120-92 sets exactly one numeric standard and declares every other one N/A: minimum lot frontage N/A, minimum lot area N/A, maximum lot coverage N/A, side and rear yards N/A unless the lot adjoins a residential district, in which case each takes that district's required setback. THE FRONT SETBACK IS THE SINGLE RECORDABLE FIGURE AND IT IS CONDITIONAL: the average front yard depth of buildings along the block, OR 35 FEET IF NO BUILDINGS STAND WITHIN 500 FEET of the proposed building. The recorded 35 is that isolated-site case, which is the normal condition in an open-space parcel and therefore the figure most likely to apply, but on a block with neighbouring buildings the average governs instead. The nulls here are the code's own N/As, not missing research. Note that a former maximum BUILDING coverage standard was repealed 9-19-2017 by Ord. No. 2017-299 and the surviving lot coverage line reads N/A, so O-S caps building footprint by nothing at all.R-1 permits single-family ATTACHED dwellings by right alongside detached, at 3,000 sq ft of lot per unit
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. NO SHORT-TERM RENTAL PROVISION EXISTS ANYWHERE IN THE ROCHESTER CITY CODE TODAY, AND THE REASON THE SECONDARY SOURCES DISAGREE IS NOW KNOWN: STR REGULATION IS SITTING IN A PENDING COMPREHENSIVE REZONE THAT HAS NOT BEEN ADOPTED. As of 2026-08-12 all 121 chapters of the live code were enumerated and none is a rental-licensing or lodging chapter; an eCode360 full-text search of RO0104 for 'short-term rental' returns only Sec. 23-19 Short-term water shutoff, Sec. 120-151 Vehicle rental services and a definitions hit; and the City's own site search surfaces no STR permit page, application or fee schedule. So there is no STR permit regime in force, and the industry blogs asserting one since 1-1-2023 are wrong. WHAT IS ACTUALLY HAPPENING: the Zoning Alignment Project (ZAP, rochesterzap.com) would create TWO new STR uses, and its Final Draft STR Code Amendment is dated April 2026. 'Short-Term Rental, Whole Dwelling Unit' is the rental of an entire unit for under 30 consecutive days where the owner does NOT reside there; 'Short-Term Rental, Individual Sleeping Units' is the rental of sleeping rooms inside the owner's primary residence, which must keep at least one bedroom for the owner's exclusive use, and expressly includes the traditional bed-and-breakfast. THE HEADLINE RULE IS A 25% CONVERSION CEILING WITH A HOTEL TRIPWIRE: any multi-family or mixed-use development where 25% OR MORE of the units are short-term rentals is DEEMED A HOTEL and regulated as one. Under the draft use table, whole-dwelling STR is permitted or special-permit in the three residential districts (LDR, MDR, HDR) and permitted outright in most mixed-use and commercial districts, but the permission turns on OWNER OCCUPANCY: in owner-occupied structures one unit is allowed by right, while in NON-owner-occupied single-family, attached, townhouse and 2-4 family structures a unit is allowed only by SPECIAL PERMIT. Individual-sleeping-unit STR is special-permit almost everywhere. Draft operating standards: no exterior or interior alteration changing residential character, only rooms originally designed as bedrooms used for sleeping, a local manager reachable 24 hours and based within 30 miles, one non-illuminated one-square-foot sign for whole-dwelling and no signs at all for sleeping units, no RV/camper/tent or outdoor overnight occupancy, and no eating-and-drinking establishment though meals may be served to registered guests. Parking is 1 space per whole-dwelling STR and 0.5 per sleeping unit. STRs are additionally PROHIBITED outright in both the North and South Areas of the Dewey-Driving Park Urban Renewal District. NONE OF THIS IS LAW. Verified against the City Clerk's own record on 2026-08-12: the City Planning Commission voted its recommendation to Council on 2026-07-13; the 2026-07-28 Council meeting agenda and its 95 pages of Certified Ordinances contain NO zoning-code item, only two unrelated Zoning Map amendments held in committee since January and March; and the 2026-08-25 Council agenda, whose introductories closed 2026-08-04, runs Int. Nos. 306-324 with no ZAP item and no zoning code among the items held in committee. So ZAP cannot become law before the September 2026 Council cycle at the earliest. UNDERWRITE ROCHESTER STR AGAINST TODAY'S CODE, WHICH IS SILENT, BUT PRICE THE 25% HOTEL TRIPWIRE AND THE NON-OWNER-OCCUPIED SPECIAL PERMIT AS LIVE RISKS ON ANY HOLD LONGER THAN A YEAR. ABSENCE IS NOT PERMISSION IN THE MEANTIME: Ch. 120 defines permitted uses as a closed list and transient lodging is not among the permitted residential uses in R-1, R-2 or R-3, so an STR may already be unpermitted as an unlisted use even though no chapter names it. Chapter 90 Property Code's certificate-of-occupancy requirement for rental dwellings is the lever the City holds today, and New York State's 2025 statewide registry (Ch. 99 of the Laws of 2025) obliges every host to register regardless. Confirm with the Bureau of Zoning at (585) 428-6995. Separate question from whether you can build the unit.
- Building dept(585) 428-6526
Sizing up a specific parcel in Rochester?
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 Rochester runs $204–268/sq ft, about $370k–480k at 1,800 sq ft , plus roughly $5,740 for a conforming lot. See what it costs to build a house in Rochester.
ADU cost in nearby towns
All Monroe County towns: Brighton · Chili · Clarkson · Gates · Greece · Hamlin · Henrietta · Irondequoit · Mendon · Ogden · Parma · Penfield · Perinton · Pittsford · Riga · Rush · Sweden · Webster · Wheatland · Town/Village of East Rochester (Village) · Brockport (Village) · Churchville (Village) · Fairport (Village) · Hilton (Village) · Honeoye Falls (Village) · Pittsford (Village) · Scottsville (Village) · Spencerport (Village) · Webster (Village)
More on Rochester: Can you build an ADU here? · Zoning for new construction · Monroe County build cost
ADU cost in Rochester: common questions
How much does it cost to build an ADU in Rochester, NY?
An 800 sq ft accessory dwelling unit in City of Rochester 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 Rochester?
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 Rochester?
City of Rochester has 7 districts. All districts prohibit ADUs. Check the specific address with the free ADU checker or confirm with the building department at (585) 428-6526 before you spend money on design.
Can I rent an ADU in Rochester short term?
No local short-term-rental law on record - which is not the same as permission for City of Rochester. 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 City of Rochester vary by district and often carry exceptions this page does not show; zoning last reviewed 2026-08-12; verify with the building department at (585) 428-6526 before relying on any answer. Sources: Offsite / Aldo cost engine (costEngine.js + constants.js); zoning dataset (municipalData.js).