Brighton · ADU cost
What it costs to build an ADU in Brighton, NY
An 800 sq ft accessory dwelling unit in Brighton 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 Brighton maps 8 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 Brighton
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 Brighton 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 |
|---|---|---|---|---|
| RLL Residential - Large Lot | 1 ac | 75 / 22.5 / 60 ft | 30 ft | No |
| RLA Residential - Low Density | 0.53 ac | 60 / 18.75 / 60 ft | 30 ft | No |
| RLB Residential - Low Density | 0.31 ac | 40 / 13.5 / 40 ft | 30 ft | No |
| RLC Residential - Low Density | 0.26 ac | 40 / 11.25 / 40 ft | 30 ft | No |
| RM Residential - Medium Density | 0.16 ac | 35 / 5.5 / 40 ft | 30 ft | No |
| PRD Planned Residential Development | 5 ac | 30 / 10 / 20 ft | 40 ft | No |
| RHD-1 Residential - High Density | 0.92 ac | 60 / 40 / 45 ft | 80 ft | No |
| RHD-2 Residential - High Density | 0.46 ac | 40 / 30 / 35 ft | 40 ft | No |
RLL Residential - Large Lot, RLB Residential - Low Density, RLC Residential - Low Density - Livable floor area has a maximum as well as a minimum: 1,908 sq ft plus 57 sq ft for each 1,000 sq ft of lot area, so a large house on a modest lot can fail on this cap before it fails on coverage.
- The side yard is 15% of the lot width with a ceiling of 40 ft, so it shrinks on a narrower lot and grows on a wider one; a 200 ft wide lot owes 30 ft a side.
- On a 13,500 sq ft lot the floor area cap comes to about 2,678 sq ft.
- Incentive zoning under Chapter 209, Article II, can modify the floor area cap.
- An attached garage is capped separately at 900 sq ft.
RLA Residential - Low Density - Livable floor area is capped at 1,908 sq ft plus 57 sq ft for each 1,000 sq ft of lot area, about 3,226 sq ft at the district minimum lot, which leaves a narrow band above the 1,800 sq ft minimum.
- The side yard is 15% of the lot width with a ceiling of 40 ft, so it shrinks on a narrower lot and grows on a wider one; a 200 ft wide lot owes 30 ft a side.
- On a 13,500 sq ft lot the floor area cap comes to about 2,678 sq ft.
- Incentive zoning under Chapter 209, Article II, can modify the floor area cap.
- An attached garage is capped separately at 900 sq ft.
RM Residential - Medium Density - Livable floor area has a maximum as well as a minimum: 1,908 sq ft plus 57 sq ft for each 1,000 sq ft of lot area, so a large house on a modest lot can fail on this cap before it fails on coverage.
- Side yards are 10% of the lot width for one side and 25% for both together, and both grow on a wider lot.
- On a 13,500 sq ft lot the floor area cap comes to about 2,678 sq ft.
- Incentive zoning under Chapter 209, Article II, can modify the floor area cap.
- An attached garage is capped separately at 900 sq ft.
PRD Planned Residential Development - The 5 acres is the minimum for the whole development, not for each lot, and yield is capped at six dwelling units per gross acre. The front yard is 100 ft on a state or county road and 40 ft on a Town collector street.
- A semidetached lot takes 30 ft of width and 800 sq ft of livable floor area per unit; an attached lot 20 ft and 600 sq ft, 60% of what a detached house needs, with 5 ft between units.
- A yard on a project boundary line that is not a street is 30 ft.
- The 10 ft side yard applies only where a side yard is provided.
- Each dwelling unit needs 1,200 sq ft of usable open space.
- No building may contain more than five dwelling units or be longer than 150 ft.
- Individual lots have no published lot area, only a width that depends on the dwelling type.
RHD-1 Residential - High Density - The land requirement is 8,000 sq ft for the first dwelling unit and 1,000 sq ft for each additional one, on a lot of at least 40,000 sq ft.
- Where individual lots each hold their own unit the standard differs: a minimum lot area of 1,200 sq ft (0.0275 acres), a width of 14 ft and a depth of 80 ft, and an end unit owes a 30 ft side yard.
- Each dwelling unit also needs 600 sq ft of usable open space.
RHD-2 Residential - High Density - The land requirement is 10,000 sq ft for the first dwelling unit and 2,700 sq ft for each additional one, on a lot of at least 20,000 sq ft. A density cap of 14 units per acre also applies and is what usually binds.
- Where individual lots each hold their own unit the standard differs: a minimum lot area of 1,200 sq ft (0.0275 acres), a width of 14 ft and a depth of 80 ft, and an end unit owes a 30 ft side yard.
- Each dwelling unit needs 600 sq ft of usable open space.
Size limits on record in Brighton
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 Brighton:
- RLL Residential - Large LotAccessory uses in those districts are limited to non-habitable items such as a pool, gazebo, shed or cabana, one private garage of up to 600 sq ft and a horticultural building of up to 336 sq ft.
- RLA Residential - Low DensityAccessory uses in those districts are limited to non-habitable items such as a pool, gazebo, shed or cabana, one private garage of up to 600 sq ft and a horticultural building of up to 336 sq ft.
- RLB Residential - Low DensityAccessory uses in those districts are limited to non-habitable items such as a pool, gazebo, shed or cabana, one private garage of up to 600 sq ft and a horticultural building of up to 336 sq ft.
- RLC Residential - Low DensityAccessory uses in those districts are limited to non-habitable items such as a pool, gazebo, shed or cabana, one private garage of up to 600 sq ft and a horticultural building of up to 336 sq ft.
- RM Residential - Medium DensityAccessory uses in those districts are limited to non-habitable items such as a pool, gazebo, shed or cabana, one private garage of up to 600 sq ft and a horticultural building of up to 336 sq ft.
- PRD Planned Residential DevelopmentAccessory uses in those districts are limited to non-habitable items such as a pool, gazebo, shed or cabana, one private garage of up to 600 sq ft and a horticultural building of up to 336 sq ft.
- RHD-1 Residential - High DensityAccessory uses in those districts are limited to non-habitable items such as a pool, gazebo, shed or cabana, one private garage of up to 600 sq ft and a horticultural building of up to 336 sq ft.
- RHD-2 Residential - High DensityAccessory uses in those districts are limited to non-habitable items such as a pool, gazebo, shed or cabana, one private garage of up to 600 sq ft and a horticultural building of up to 336 sq ft.
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 Brighton has no local short-term rental law, and that is not the same as permission. Confirm with the Building and Planning Department before counting on renting a home short term. Separate question from whether you can build the unit.
- Zoning codeecode360.com/9441732
- Building dept(585) 784-5250
Sizing up a specific parcel in Brighton?
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Building a full house instead?
A standard-finish house in Brighton runs $204–268/sq ft, about $370k–480k at 1,800 sq ft , plus roughly $2,720 for a conforming lot. See what it costs to build a house in Brighton.
ADU cost in nearby towns
All Monroe County towns: Rochester (City) · 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) · Webster (Village)
More on Brighton: Can you build an ADU here? · Zoning for new construction · Monroe County build cost
ADU cost in Brighton: common questions
How much does it cost to build an ADU in Brighton, NY?
An 800 sq ft accessory dwelling unit in Town of Brighton 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 Brighton?
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 Brighton?
Town of Brighton has 8 districts. All districts prohibit ADUs. Check the specific address with the free ADU checker or confirm with the building department at (585) 784-5250 before you spend money on design.
Can I rent an ADU in Brighton short term?
No local short-term-rental law on record - which is not the same as permission for Town of Brighton. 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 Brighton vary by district and often carry exceptions this page does not show; zoning last reviewed 2026-08-10; verify with the building department at (585) 784-5250 before relying on any answer. Sources: the Offsite / Aldo cost engine and zoning dataset.