Clarkson · ADU cost
What it costs to build an ADU in Clarkson, NY
An 800 sq ft accessory dwelling unit in Clarkson 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 Clarkson maps 3 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 Clarkson
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 Clarkson 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 |
|---|---|---|---|---|
| Agricultural Residential (AR) — 2 acres with 200 ft of lot width, 25% maximum lot coverage and 35 ft maximum height. Front setback 40 ft on a MINOR road and 75 ft on a MAJOR road (table note 4); side 25 ft; rear 30 ft to a dwelling or attached garage and 10 ft to any other structure (table note 1). A TWO-FAMILY DWELLING IS ALLOWED AT IDENTICAL DIMENSIONS to the single-family row (2 acres, 200 ft, same setbacks, same 25% coverage, same 35 ft height), so a second unit costs no additional LAND — but it is a SPECIALLY PERMITTED use, not a right, and so is the accessory dwelling unit. Both sit under the 'Specially Permitted Uses' block of the § 140-20.3 table rather than the 'Permitted Uses' block, and the table carries no per-row P/SP marker, so the distinction is visible only in the section header above the row. AR therefore offers two routes to a second unit at no extra acreage, each requiring a special permit and neither available as of right. A detached ADU is allowed in AR (unlike RS-10, which is internal-only), which remains the district's real advantage. AGRICULTURAL OPERATIONS ARE A SEPARATE AND MUCH LARGER ROW: 5 acres with 250 ft of width, 100 ft front, 35 ft side and 60 ft rear, and their height cap does not apply to barns, silos, water towers or tanks, windmills or other farm buildings on active farmland (table note 3). THE TABLE IS USE-KEYED, NOT DISTRICT-KEYED, AND THAT IS THE CENTRAL READING HAZARD IN THIS TOWN: each district's table lists one row per permitted use, each with its own lot size, width, setbacks, coverage and height, so 'the AR minimum lot' is meaningless without naming the use. The 2 acres recorded here is the single-family dwelling row. | 2 ac | 40 / 25 / 30 ft | 35 ft | Special permit |
| Residential Suburban — 20,000 sf (RS-20) — 20,000 sf (0.46 acres) with 100 ft of lot width, 30% maximum lot coverage and 35 ft maximum height. Front setback 40 ft on a minor road and 75 ft on a major road (table note 3); side 10 ft; rear 30 ft to a dwelling or attached garage and 10 ft to other structures (table note 1). The district name states its own minimum lot, which makes this one of the few self-documenting districts in the county. A TWO-FAMILY DWELLING IS ALLOWED ON THE SAME 20,000 SF AT THE SAME SETBACKS AND COVERAGE as a single-family — no extra land is required for the second unit — and a DETACHED ADU is allowed on top of that under § 140-23.4. SO AN RS-20 LOT CAN REACH THREE UNITS ON THE MINIMUM ACREAGE, BUT NOT AS OF RIGHT: both the two-family and the ADU are SPECIALLY PERMITTED uses under the § 140-20.4 table, so each needs its own special permit. The land is free; the approvals are not. Note that the side setback drops to 10 ft here from AR's 25 ft while the rear holds at 30 ft, so the buildable envelope narrows far less than the lot does. The ADU carries its own 10 ft side and 10 ft rear setbacks and otherwise refers to the primary use for bulk. As everywhere in this chapter the table is USE-KEYED: the figures recorded are the single-family dwelling row, and other uses permitted in RS-20 state their own dimensions. | 0.4591 ac | 40 / 10 / 30 ft | 35 ft | Special permit |
| Residential Suburban — 10,000 sf (RS-10) — 10,000 sf (0.23 acres) with 75 ft of lot width, 40% maximum lot coverage and 35 ft maximum height. Front setback 40 ft on a minor road and 75 ft on a major road (table note 3); side 10 ft; rear 30 ft to a dwelling or attached garage and 10 ft to other structures (table note 1). This is Clarkson's densest district and carries the town's highest coverage allowance at 40%. THIS DISTRICT IS THE ONE PLACE IN THE TOWN THAT PERMITS MULTIFAMILY, AND IT DOES SO IN TWO TIERS THAT ARE EASY TO CONFLATE: a multifamily dwelling of UP TO 4 UNITS needs 20,000 sf with 100 ft of width, and a multifamily dwelling of OVER 4 UNITS needs a full ACRE with 100 ft of width — both at 40% coverage but at a raised 40 FT height rather than the 35 ft that applies to one- and two-family forms, and both governed additionally by § 140-23.17. So the recorded 10,000 sf is the single-family figure and sizing a small apartment building from it would understate the land requirement by two to four times. A two-family dwelling is permitted on the same 10,000 sf as a single-family. THE ADU RULE IS NARROWER HERE THAN ELSEWHERE IN THE TOWN: in RS-10 an accessory dwelling unit may only be located WITHIN THE PRIMARY STRUCTURE, whereas AR and RS-20 permit a detached ADU — so no backyard cottage on these lots, internal conversion only. The table is USE-KEYED throughout; the figures recorded are the single-family dwelling row. | 0.2296 ac | 40 / 10 / 30 ft | 35 ft | Special permit |
Size limits on record in Clarkson
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 Clarkson:
- Agricultural Residential (AR) — 2 acres with 200 ft of lot width, 25% maximum lot coverage and 35 ft maximum height. Front setback 40 ft on a MINOR road and 75 ft on a MAJOR road (table note 4); side 25 ft; rear 30 ft to a dwelling or attached garage and 10 ft to any other structure (table note 1). A TWO-FAMILY DWELLING IS ALLOWED AT IDENTICAL DIMENSIONS to the single-family row (2 acres, 200 ft, same setbacks, same 25% coverage, same 35 ft height), so a second unit costs no additional LAND — but it is a SPECIALLY PERMITTED use, not a right, and so is the accessory dwelling unit. Both sit under the 'Specially Permitted Uses' block of the § 140-20.3 table rather than the 'Permitted Uses' block, and the table carries no per-row P/SP marker, so the distinction is visible only in the section header above the row. AR therefore offers two routes to a second unit at no extra acreage, each requiring a special permit and neither available as of right. A detached ADU is allowed in AR (unlike RS-10, which is internal-only), which remains the district's real advantage. AGRICULTURAL OPERATIONS ARE A SEPARATE AND MUCH LARGER ROW: 5 acres with 250 ft of width, 100 ft front, 35 ft side and 60 ft rear, and their height cap does not apply to barns, silos, water towers or tanks, windmills or other farm buildings on active farmland (table note 3). THE TABLE IS USE-KEYED, NOT DISTRICT-KEYED, AND THAT IS THE CENTRAL READING HAZARD IN THIS TOWN: each district's table lists one row per permitted use, each with its own lot size, width, setbacks, coverage and height, so 'the AR minimum lot' is meaningless without naming the use. The 2 acres recorded here is the single-family dwelling row.So a backyard cottage is available on the larger suburban and agricultural lots but not on the 10,000 sq ft lots
- Residential Suburban — 20,000 sf (RS-20) — 20,000 sf (0.46 acres) with 100 ft of lot width, 30% maximum lot coverage and 35 ft maximum height. Front setback 40 ft on a minor road and 75 ft on a major road (table note 3); side 10 ft; rear 30 ft to a dwelling or attached garage and 10 ft to other structures (table note 1). The district name states its own minimum lot, which makes this one of the few self-documenting districts in the county. A TWO-FAMILY DWELLING IS ALLOWED ON THE SAME 20,000 SF AT THE SAME SETBACKS AND COVERAGE as a single-family — no extra land is required for the second unit — and a DETACHED ADU is allowed on top of that under § 140-23.4. SO AN RS-20 LOT CAN REACH THREE UNITS ON THE MINIMUM ACREAGE, BUT NOT AS OF RIGHT: both the two-family and the ADU are SPECIALLY PERMITTED uses under the § 140-20.4 table, so each needs its own special permit. The land is free; the approvals are not. Note that the side setback drops to 10 ft here from AR's 25 ft while the rear holds at 30 ft, so the buildable envelope narrows far less than the lot does. The ADU carries its own 10 ft side and 10 ft rear setbacks and otherwise refers to the primary use for bulk. As everywhere in this chapter the table is USE-KEYED: the figures recorded are the single-family dwelling row, and other uses permitted in RS-20 state their own dimensions.So a backyard cottage is available on the larger suburban and agricultural lots but not on the 10,000 sq ft lots
- Residential Suburban — 10,000 sf (RS-10) — 10,000 sf (0.23 acres) with 75 ft of lot width, 40% maximum lot coverage and 35 ft maximum height. Front setback 40 ft on a minor road and 75 ft on a major road (table note 3); side 10 ft; rear 30 ft to a dwelling or attached garage and 10 ft to other structures (table note 1). This is Clarkson's densest district and carries the town's highest coverage allowance at 40%. THIS DISTRICT IS THE ONE PLACE IN THE TOWN THAT PERMITS MULTIFAMILY, AND IT DOES SO IN TWO TIERS THAT ARE EASY TO CONFLATE: a multifamily dwelling of UP TO 4 UNITS needs 20,000 sf with 100 ft of width, and a multifamily dwelling of OVER 4 UNITS needs a full ACRE with 100 ft of width — both at 40% coverage but at a raised 40 FT height rather than the 35 ft that applies to one- and two-family forms, and both governed additionally by § 140-23.17. So the recorded 10,000 sf is the single-family figure and sizing a small apartment building from it would understate the land requirement by two to four times. A two-family dwelling is permitted on the same 10,000 sf as a single-family. THE ADU RULE IS NARROWER HERE THAN ELSEWHERE IN THE TOWN: in RS-10 an accessory dwelling unit may only be located WITHIN THE PRIMARY STRUCTURE, whereas AR and RS-20 permit a detached ADU — so no backyard cottage on these lots, internal conversion only. The table is USE-KEYED throughout; the figures recorded are the single-family dwelling row.So a backyard cottage is available on the larger suburban and agricultural lots but not on the 10,000 sq ft lots
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 rentalsShort-term rentals allowed with local rules. CLARKSON IS THE FIRST MONROE TOWN WITH A PURPOSE-BUILT SHORT-TERM RENTAL LAW INSIDE ITS ZONING CODE, and it is the clearest STR finding in the county so far. § 140-23.21 Short-term rentals (STRs) sits in Article 23 Additional Use Regulations alongside a separate § 140-23.9 Bed-and-breakfasts, so the two are regulated as distinct uses rather than conflated. The stated purpose is explicit that the Town 'welcomes visitors' but that OVERCONCENTRATION of STRs may disrupt the peace, quiet and enjoyment of residents, and the section is framed as a balance between owners who wish to offer STRs and neighbours who do not. Operational requirements read so far: no STR is permitted on any property in violation of the Zoning Code or the NYS Uniform Fire Prevention and Building Code; the use must accommodate its MINIMUM OFF-STREET PARKING REQUIREMENT ENTIRELY ON SITE; and there is a further restriction on where off-street parking may be placed. TREAT THE PERMIT QUESTION AS OPEN: strStatus is recorded as regulated rather than registration_required precisely because no registration or permit clause was confirmed. Note also that a keyword sweep of the 52-chapter Town Code TOC found NO separate rental-licensing chapter of the Gates Ch. 148 kind, so § 140-23.21 appears to be the whole regime, but that should be confirmed when the section is read in full. New York State's 2025 statewide short-term rental registry (Ch. 99 of the Laws of 2025) obliges every host to register regardless of local law. Confirm with the Building Department at (585) 637-1145. Separate question from whether you can build the unit.
- Building dept(585) 637-1145
Sizing up a specific parcel in Clarkson?
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 Clarkson runs $204–268/sq ft, about $370k–480k at 1,800 sq ft , plus roughly $865 for a conforming lot. See what it costs to build a house in Clarkson.
ADU cost in nearby towns
All Monroe County towns: Rochester (City) · Brighton · Chili · 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 Clarkson: Can you build an ADU here? · Zoning for new construction · Monroe County build cost
ADU cost in Clarkson: common questions
How much does it cost to build an ADU in Clarkson, NY?
An 800 sq ft accessory dwelling unit in Town of Clarkson 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 Clarkson?
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 Clarkson?
Town of Clarkson has 3 districts. All districts allow ADUs with a special-use permit. Check the specific address with the free ADU checker or confirm with the building department at (585) 637-1145 before you spend money on design.
Can I rent an ADU in Clarkson short term?
Short-term rentals allowed with local rules for Town of Clarkson. 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 Clarkson vary by district and often carry exceptions this page does not show; zoning last reviewed 2026-08-13; verify with the building department at (585) 637-1145 before relying on any answer. Sources: Offsite / Aldo cost engine (costEngine.js + constants.js); zoning dataset (municipalData.js).