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Amherst · ADU cost

What it costs to build an ADU in Amherst, NY

800 sq ft ≈ $200k–260k $249–327/sq ft 27 districts National Grid

An 800 sq ft accessory dwelling unit in Amherst 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 Amherst maps 27 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 Amherst

Standard finish, slab on grade, on a flat and clear part of the lot, general-contractor margin included. These are structure costs at Erie County pricing, before the service and septic work a second dwelling can trigger.

SizeType$ / sq ftEstimated 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 ADUIf it scaled with floor areaFixed 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 Amherst 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 District 3 ac 50 / - / - ft 35 ft Special permit
Suburban Agricultural District 1 ac 50 / - / - ft 35 ft Special permit
Residential District One 0.5 ac 30 / 8 / 35 ft 35 ft Special permit
Residential District Two 0.26 ac 30 / 8 / 35 ft 35 ft Special permit
Residential District Three 0.19 ac 30 / 5 / 30 ft 35 ft Special permit
Cluster Residential District Three-A 0.12 ac 25 / 0 / 30 ft 35 ft Special permit
Traditional Single-Family Residential District 0.1 ac 25 / 5 / 25 ft 35 ft No
Residential District Four 0.13 ac 30 / 8 / 30 ft 35 ft Special permit
Multifamily Residential District Four-A 0.14 ac 25 / 5 / 20 ft 35 ft Special permit
Multifamily Residential District Five 0.083 ac — 35 ft Special permit
Multifamily Residential District Six 0.14 ac 25 / - / - ft 35 ft Special permit
Multifamily Residential District Seven 0.14 ac 20 / - / - ft 65 ft No
Manufactured Home Residential District Eight 0.092 ac 30 / 15 / 15 ft — No
Office Building District — 20 / 15 / 15 ft 65 ft No
Neighborhood Business District — 20 / 10 / 15 ft 30 ft No
General Business District — 20 / 10 / 15 ft 65 ft No
Commercial Service District 1 ac 20 / 10 / 10 ft 40 ft No
Motor Service District — 20 / 10 / 25 ft 65 ft No
Shopping Center District 10 ac 25 / 50 / 50 ft 65 ft No
Research and Development District 1 ac 20 / 15 / 15 ft 65 ft No
Science Technology District 2 ac 20 / 30 / 30 ft 45 ft No
General Industrial District 1 ac 20 / 15 / 15 ft 65 ft No
Agricultural District 5 ac 50 / 30 / 30 ft 35 ft Special permit
Traditional Neighborhood Development District — 0 / 15 / 15 ft 50 ft No
Live-Work District 1 — 25 / 5 / 25 ft 35 ft Special permit
Community Facilities District — 20 / 15 / 15 ft 65 ft No
Recreation Conservation District — 20 / 15 / 15 ft 65 ft No

Rural Residential District - The three-acre minimum is stated per dwelling, not per lot. Side and rear yards are not fixed: they are never less than 30 ft where the lot adjoins a residential district, and a building over 35 ft tall must stand back three feet for every foot of its height.

  • On a corner lot the exterior side yard must meet the 50 ft front-yard figure
  • A through lot owes a rear yard equal to the front yard required of the lots facing the other street
  • Where buildings already occupy half a block and sit further back than 50 ft, 85% of that average applies instead
  • A non-residential building may reach 65 ft
  • A rural cluster subdivision needs at least 15 acres with half of it kept as open space, one unit per three acres, and one-acre lots 150 ft wide

Suburban Agricultural District - The one-acre minimum is stated per dwelling, not per lot. Side and rear yards are not fixed: they are never less than 30 ft where the lot adjoins a residential district, and three feet are added for every foot of building height above 35 ft.

  • A dwelling of two storeys or more must contain at least 1,200 sq ft
  • On a corner lot the exterior side yard must meet the 50 ft front-yard figure
  • A non-residential building may reach 65 ft

Residential District One - Eight feet is the least either side yard may be, and the two sides together must add to 20 ft, so a house cannot be pushed to one side of a narrow lot. The 21,780 sq ft minimum is stated per dwelling.

  • A dwelling of more than one storey must contain at least 1,400 sq ft
  • On a corner lot the exterior side yard must meet the 30 ft front-yard figure
  • A through lot owes a rear yard equal to the front yard required of the lots facing the other street

Residential District Two - Eight feet is the least either side yard may be, and the two sides together must add to 20 ft. The 11,500 sq ft minimum is stated per dwelling.

  • A dwelling of more than one storey must contain at least 1,400 sq ft
  • On a corner lot the exterior side yard must meet the 30 ft front-yard figure

Residential District Three - A corner lot is priced higher than an interior one: 9,750 sq ft on 75 ft of width rather than 8,450 sq ft on 65 ft. The lot area is stated per dwelling.

  • Five feet is the least either side yard may be, and the two sides together must add to 10 ft
  • A dwelling of two storeys or more must contain at least 1,200 sq ft
  • The corner-lot exterior side yard must meet the 30 ft front-yard figure

Cluster Residential District Three-A - No side yard is required at all, and spacing is controlled instead by a 10 ft minimum separation between buildings. The 5,000 sq ft minimum is stated per dwelling.

  • A dwelling of two storeys or more must contain at least 1,200 sq ft
  • Dwellings may be arranged in groups, in which case each group must abut a street and 30% of the site must be kept as common open space

Traditional Single-Family Residential District - A corner lot is priced higher than an interior one: 5,800 sq ft on 50 ft of width rather than 4,500 sq ft on 40 ft. The lot area is stated per dwelling.

  • Five feet is the least either side yard may be, and the two sides together must add to 10 ft
  • The corner-lot exterior side yard must meet the 25 ft front-yard figure

Residential District Four - Width is priced by the number of dwellings in the building: 90 ft for a two-family, 105 ft for a three-family and 120 ft for a four-family. The 5,850 sq ft minimum is stated per dwelling, so a four-family building needs 23,400 sq ft.

  • Eight feet is the least either side yard may be, and the two sides together must add to 20 ft
  • Minimum dwelling size rises with bedroom count, from 400 sq ft for a studio through 640, 760 and 1,000 sq ft to 1,200 sq ft for four bedrooms

Multifamily Residential District Four-A - Three different standards run here, one per development form. The figures shown are for a detached house on its own lot, where a corner lot is priced at 7,200 sq ft and 60 ft of width.

  • Detached houses not on individual lots are governed by density instead: one unit per 6,000 sq ft, with buildings kept 10 ft apart and 5 ft off any lot line
  • Attached dwellings need 4,300 sq ft of land each on a lot at least 120 ft wide, with 30 ft front, 40 ft rear and 40 ft side yards
  • The Planning Board may reduce the side yard below five feet at plat or site-plan approval if buildings stay 10 ft apart

Multifamily Residential District Five - Land per dwelling is priced by bedroom count: 3,630 sq ft for a studio or one bedroom, 4,356 for two, 5,445 for three and 6,250 for four.

  • Yards and building spacing are not fixed figures: two parallel buildings must stand apart by 1.66 times their average height
  • A building whose longer wall faces a lot line must stand back twice its own height, and never closer than 36 ft to a street line
  • Attached dwellings may alternatively be built to the R-4 district standards
  • Minimum dwelling size rises with bedroom count, from 400 sq ft for a studio to 1,200 sq ft for four bedrooms

Multifamily Residential District Six - Three different standards run here, one per development form. The figures shown are for a detached house on its own lot, where a corner lot is priced at 7,200 sq ft and 60 ft of width.

  • That detached house's side and rear yards are never less than 30 ft against a residential district, with three feet added for every foot of building height above 35 ft
  • Detached houses not on individual lots are governed by density instead: one unit per 6,000 sq ft, capped at eight units on any one lot, with buildings 10 ft apart and 5 ft off a lot line
  • Attached dwellings are the densest form here: 2,562 sq ft of land for a studio or one bedroom rising to 4,356 sq ft for four bedrooms, on a lot at least 200 ft wide
  • For attached dwellings the height limit rises to 65 ft

Multifamily Residential District Seven - The front setback is height-linked: 20 ft for the first 35 ft of building height and 30 ft for any part of the building above that. A corner lot must be 60 ft wide rather than 50 ft.

  • Side spacing is stated building to building at 10 ft
  • The rear yard and the distance to a lot line are never less than 30 ft against a residential district, with three feet added for every foot of building height above 35 ft
  • Attached dwellings are sized differently: 725 sq ft of land for a studio or one bedroom and 1,000 sq ft for two or more, on a lot at least 100 ft wide, with 30 ft between buildings
  • A dwelling of two storeys or more must contain at least 1,200 sq ft

Manufactured Home Residential District Eight - The figures shown are for a lot inside the park. The park itself must be at least 10 acres, hold at least 50 lots, be at least 100 ft wide, keep 8% of its gross area as recreation land and hold every structure 25 ft back from the park boundary.

  • The front yard is 30 ft on a public street and 25 ft on a private one
  • Homes must stand 20 ft apart

Office Building District - The 15 ft side and rear yards apply against another non-residential lot and rise to 25 ft once the building reaches 30 ft; against a residential district they are never less than 30 ft, with three feet added for every foot of height above 35 ft.

  • The front setback is 20 ft for the first 35 ft of building height and 30 ft above that
  • The district sets no minimum lot area and no minimum lot width
  • Buildings on the same site must stand 30 ft apart

Neighborhood Business District - The one-acre figure this district publishes is a maximum lot area, not a minimum: a lot here may not exceed an acre, and there is no floor.

  • The front setback is 20 ft for the first two storeys and 30 ft for anything above
  • The side and rear yards shown apply against another non-residential lot; against a residential district the rear yard is 30 ft and the side yard 15 ft
  • A side yard may be nothing at all where the building sits on the lot line, but must be at least 10 ft if it does not

General Business District - The 10 ft side and 15 ft rear yards apply against another non-residential lot and rise to 25 ft once the building reaches 30 ft; against a residential district they are never less than 30 ft, with three feet added for every foot of height above 35 ft.

  • A side yard may be nothing at all where the building sits on the lot line, but must be at least 10 ft if it does not
  • The front setback is 20 ft for the first 35 ft of building height and 30 ft above that
  • The district sets no minimum lot area and no minimum lot width

Commercial Service District - The 10 ft side and rear yards apply against another non-residential lot; against a residential district both rise to 50 ft.

  • The front setback is 20 ft for the first 35 ft of building height and 30 ft above that

Motor Service District - The side and rear yards shown apply against another non-residential lot; against a residential district they are never less than 30 ft, with three feet added for every foot of building height above 35 ft.

  • The front setback is 20 ft for the first 35 ft of building height and 30 ft above that
  • The district sets no minimum lot area; the site standards for motor service uses are set at § 6-4-12 instead
  • Buildings on the same site must stand 30 ft apart

Shopping Center District - The 50 ft side and rear yards apply against another non-residential lot; against a residential district they are never less than 30 ft, with three feet added for every foot of building height above 35 ft.

  • The front setback is 25 ft for the first 35 ft of building height and 30 ft above that
  • The district sets no minimum lot width
  • Buildings on the same site must stand 30 ft apart

Research and Development District - A Research and Development district must cover at least 10 acres, and a lot within it must be at least one acre.

  • The 15 ft side and rear yards apply against another non-residential lot, and rise to 25 ft once the building reaches 30 ft
  • Against a residential district the side and rear yards are never less than 30 ft, with three feet added for every foot of building height above 35 ft
  • The front setback is 20 ft for the first 35 ft of building height and 30 ft above that
  • Buildings on the same site must stand 30 ft apart

Science Technology District - A Science Technology district must cover at least 10 acres, and a lot within it must be at least two acres.

  • The 30 ft side and rear yards apply against another non-residential lot and rise to 40 ft once the building reaches 30 ft
  • Against a residential district the side and rear yards are 50 ft, rising to 75 ft once the building reaches 30 ft
  • The front setback is 20 ft for the first 35 ft of building height and 30 ft above that
  • Buildings on the same site must stand 30 ft apart

General Industrial District - The 15 ft side and rear yards apply against another non-residential lot and rise to 25 ft once the building reaches 30 ft; against a residential district they are never less than 30 ft, with three feet added for every foot of height above 35 ft.

  • The front setback is 20 ft for the first 35 ft of building height and 30 ft above that
  • Buildings on the same site must stand 30 ft apart

Agricultural District - Five acres is both the minimum lot area and the land required per dwelling, so a second house needs a second five acres.

  • Side and rear yards are never less than 30 ft against a residential district, with three feet added for every foot of building height above 35 ft
  • The 15% coverage cap applies to residential use only
  • A non-residential building may reach 65 ft

Traditional Neighborhood Development District - This district works the opposite way round: there is no minimum front setback and instead a maximum of six feet, so a building must be built out to the street rather than back from it. There is a minimum height of 26 ft as well.

  • A Traditional Neighborhood Development district must cover at least 40 acres
  • The 15 ft side and rear yards apply where the lot abuts a residential district; against another non-residential lot no yard is required at all
  • Parking and other vehicle areas stand back 25 ft from a residential district and 15 ft otherwise
  • Buildings inside the site need no separation

Live-Work District 1 - The side and rear yards shown are the same whether or not the lot abuts a residential district, but parking and other vehicle areas stand back 15 ft from a residential district and 5 ft from the street.

  • A detached dwelling of two storeys or more must contain at least 1,200 sq ft
  • An attached dwelling is sized by bedroom count instead, from 400 sq ft for a studio through 640, 760 and 1,000 sq ft to 1,200 sq ft for four bedrooms
  • The corner-lot exterior side yard must meet the 25 ft front-yard figure

Community Facilities District - The 15 ft side and rear yards apply against another non-residential lot; against a residential district they are never less than 30 ft, with three feet added for every foot of building height above 35 ft.

  • The district sets no minimum lot area and no minimum lot width
  • The front setback is 20 ft for the first 35 ft of building height and 30 ft above that
  • Parking and other vehicle areas stand back 10 ft from a residential district and 5 ft otherwise

Recreation Conservation District - The 15 ft side and rear yards apply against another non-residential lot; against a residential district both rise to 50 ft.

  • The district sets no minimum lot area and no minimum lot width
  • The front setback is 20 ft for the first 35 ft of building height and 30 ft above that
  • Parking and other vehicle areas stand back 25 ft from a residential district and 5 ft otherwise
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Size limits on record in Amherst

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 Amherst:

Costs an ADU adds that a house does not

Sizing up a specific parcel in Amherst?

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 Amherst runs $204–268/sq ft, about $370k–480k at 1,800 sq ft , plus roughly $3,901 for a conforming lot. See what it costs to build a house in Amherst.

ADU cost in nearby towns

Buffalo (City)
800 sq ft ≈ $200k–260k
Lackawanna (City)
800 sq ft ≈ $200k–260k
Tonawanda (City)
800 sq ft ≈ $200k–260k
Alden
800 sq ft ≈ $200k–260k
Aurora
800 sq ft ≈ $200k–260k
Boston
800 sq ft ≈ $200k–260k

All Erie County towns: Buffalo (City) · Lackawanna (City) · Tonawanda (City) · Alden · Aurora · Boston · Brant · Cheektowaga · Clarence · Colden · Collins · Concord · Eden · Elma · Evans · Grand Island · Hamburg · Holland · Lancaster · Marilla · Newstead · North Collins · Orchard Park · Sardinia · Tonawanda · Wales · West Seneca · Akron (Village) · Alden (Village) · Angola (Village) · Blasdell (Village) · Depew (Village) · East Aurora (Village) · Farnham (Village) · Gowanda (Village) · Hamburg (Village) · Kenmore (Village) · Lancaster (Village) · North Collins (Village) · Orchard Park (Village) · Sloan (Village) · Springville (Village) · Williamsville (Village)

More on Amherst: Can you build an ADU here? · Zoning for new construction · Erie County build cost

ADU cost in Amherst: common questions

How much does it cost to build an ADU in Amherst, NY?

An 800 sq ft accessory dwelling unit in Town of Amherst 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 Amherst?

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 Amherst?

Town of Amherst has 27 districts. 15 districts prohibit ADUs, 12 require a special-use permit. Check the specific address with the free ADU checker or confirm with the building department at (716) 631-7080 before you spend money on design.

Can I rent an ADU in Amherst short term?

Short-term rentals allowed with registration for Town of Amherst. 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 Erie 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 Amherst vary by district and often carry exceptions this page does not show; zoning last reviewed 2026-09-10; verify with the building department at (716) 631-7080 before relying on any answer. Sources: the Offsite / Aldo cost engine and zoning dataset.

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