Webster · ADU cost
What it costs to build an ADU in Webster, NY
An 800 sq ft accessory dwelling unit in Webster 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 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 Webster maps 4 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 Webster
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 Webster 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 |
|---|---|---|---|---|
| Residential R-1-13.6 District | 0.31 ac | 40 / 8 / 40 ft | 30 ft | No |
| Residential R-1-9.6 District | 0.22 ac | 40 / 6 / 40 ft | 30 ft | No |
| Residential R-2-9.6 District | 0.22 ac | 40 / 6 / 40 ft | 30 ft | No |
| Residential RM District | 0.22 ac | 40 / 6 / 40 ft | 35 ft | No |
Residential R-1-13.6 District - Under § 175-11A(2), 50% in number of the lots on any subdivision plan must be at least 16,000 sq ft, so the minimum shown is the floor for an individual lot, not an achievable average across a plan.
- Where principal structures front the same street within 300 ft of either side line, the front yard is the average of the nearest setbacks on each side, never less than 20 ft.
- With a principal structure on one side only, the front yard is the average of that setback and 40 ft, again never less than 20 ft.
- On a lot under 70 ft wide held in separate ownership when the chapter took effect, the 20 ft side yard total drops one foot per foot under 70, to no less than 12 ft.
- Once that reduced side yard total is below 16 ft, the two side yards must be equal.
- The 30 ft height limit is for dwellings and structures attached to them. Detached garages are limited to 18 ft and accessory buildings to 10 ft.
- Lot coverage counts all buildings, accessory buildings included.
Residential R-1-9.6 District - The front yard is contextual: where principal structures front the same street within 300 ft of either side line, the depth is the average of the nearest setbacks on each side, never under 20 ft. With a structure on one side only, it is the average of that setback and 40 ft.
- On a lot under 60 ft wide held in separate ownership when the chapter took effect, the 16 ft side yard total drops six inches per foot under 60, to no less than 10 ft.
- Once that reduced side yard total is below 12 ft, the two side yards must be equal.
- The 30 ft height limit is for dwellings and structures attached to them. Detached garages are limited to 18 ft and accessory buildings to 10 ft.
- Lot coverage counts all buildings, accessory buildings included.
Residential R-2-9.6 District - The figures shown are for a single-family dwelling. The front yard is contextual: where principal structures front the same street within 300 ft of either side line, the required depth is the average of the nearest setbacks on each side, never less than 20 ft.
- A two-family dwelling is a controlled site use needing site plan approval: 18,000 sq ft on 100 ft of width, with the two side yards totalling 26 ft and neither under 10 ft.
- Townhouses are sized by density: 2,000 sq ft per dwelling unit, a minimum of 1 acre for each group, and a hard cap of 8 units per acre, which is what binds.
- With a principal structure on one side only, the front yard is the average of that setback and 40 ft.
- On a lot under 60 ft wide in separate ownership when the chapter took effect, the 16 ft side yard total drops six inches per foot under 60, to no less than 10 ft, and splits equally below 12 ft.
- The 30 ft height limit is for dwellings and attached structures; detached garages are limited to 18 ft and accessory buildings to 10 ft, and lot coverage counts all buildings.
Residential RM District - The figures shown are for a single-family dwelling, and the 35 ft height covers single-family, two-family and townhouse buildings only. Two-family, townhouse, multiple-family and condominium development all require site plan review under Article XIV.
- A two-family dwelling is a controlled site use needing site plan approval: 18,000 sq ft on 100 ft of width, with the two side yards totalling 26 ft and neither under 10 ft.
- Townhouses are sized by density: 2,000 sq ft per dwelling unit, a minimum of 1 acre for each group, a hard cap of 8 units per acre, and a 40 ft side yard.
- A multiple-family dwelling needs 20,000 sq ft for the first 2 units plus 3,000 sq ft for each beyond, on 150 ft of width, and stands twice its height from a side or rear line, 80 ft at 40 ft.
- Where structures front the same street within 300 ft of either side line, the front yard is the average of the nearest setbacks, never under 20 ft; with one side only, the average of it and 40 ft.
- On a lot under 60 ft wide in separate ownership when the chapter took effect, the 16 ft side yard total drops six inches per foot under 60, to no less than 10 ft, and splits equally below 12 ft.
- Lot coverage counts all buildings, accessory buildings included.
Size limits on record in Webster
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 Webster:
- Residential R-1-13.6 DistrictAfter the alteration the lot must have at least 5,000 square feet for each dwelling unit.
- Residential R-1-9.6 DistrictAfter the alteration the lot must have at least 5,000 square feet for each dwelling unit.
- Residential R-2-9.6 DistrictAfter the alteration the lot must have at least 5,000 square feet for each dwelling unit.
- Residential RM DistrictAfter the alteration the lot must have at least 5,000 square feet for each dwelling 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 rentalsShort-term rentals prohibited. Each residential district in the Village of Webster permits only the uses on its list, and no list includes a tourist home, bed-and-breakfast, rooming or boarding house, or hotel or motel. A use absent from the list is barred. Separate question from whether you can build the unit.
- Zoning codeecode360.com/7738156
- Building dept(585) 265-3770
Sizing up a specific parcel in Webster?
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 Webster runs $204–268/sq ft, about $370k–480k at 1,800 sq ft . See what it costs to build a house in Webster.
ADU cost in nearby towns
All Monroe County towns: Rochester (City) · Brighton · Chili · Clarkson · Gates · Greece · Hamlin · Henrietta · 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)
More on Webster: Can you build an ADU here? · Zoning for new construction · Monroe County build cost
ADU cost in Webster: common questions
How much does it cost to build an ADU in Webster, NY?
An 800 sq ft accessory dwelling unit in Village of Webster 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 Webster?
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 Webster?
Village of Webster has 4 districts. All districts prohibit ADUs. Check the specific address with the free ADU checker or confirm with the building department at (585) 265-3770 before you spend money on design.
Can I rent an ADU in Webster short term?
Short-term rentals prohibited for Village of Webster. 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 Village of Webster vary by district and often carry exceptions this page does not show; zoning last reviewed 2026-08-14; verify with the building department at (585) 265-3770 before relying on any answer. Sources: the Offsite / Aldo cost engine and zoning dataset.