Northumberland · ADU cost
What it costs to build an ADU in Northumberland, NY
An 800 sq ft accessory dwelling unit in Northumberland 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 Northumberland maps 7 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 Northumberland
Standard finish, slab on grade, on a flat and clear part of the lot, general-contractor margin included. These are structure costs at Saratoga 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 Northumberland 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 |
|---|---|---|---|---|
| APD Agricultural Protection | 5 ac | 50 / 25 / 25 ft | 35 ft | No |
| R-3 Residential | 3 ac | 50 / 25 / 25 ft | 35 ft | No |
| R-1 Residential | 1 ac | 50 / 25 / 25 ft | 35 ft | No |
| MH Mobile Home | 0.21 ac | 20 / 20 / 20 ft | 35 ft | No |
| C/R Commercial/Residential | 1 ac | 50 / 25 / 25 ft | 35 ft | No |
| H Hamlet | 0.46 ac | 25 / 15 / 20 ft | 35 ft | No |
| I Industrial | 1 ac | 50 / 30 / 30 ft | 35 ft | No |
APD Agricultural Protection - The 10% coverage cap counts the house and all accessory structures together. A farm, agricultural pursuit, agricultural use structure or forestry use needs at least 10 acres on 300 ft of frontage, twice the land of a house.
- The 300 ft figure is frontage along the road, not width at the building line, where the ordinance sets no figure.
- For farms and agricultural use structures, a silo is exempt from the 35 ft height limit and capped at 90 ft instead.
- Mining needs only 1 acre but 100 ft on all three yards, and agribusinesses, sawmills and riding stables also take 100 ft yards.
- By special permit, a bed-and-breakfast, garden shop, nursing home, marina or park needs 5 acres. A nursing home also needs a 100 ft front yard and 50 ft side and rear yards.
- A home occupation needs 5 acres and a farm employee dwelling unit 10 acres.
- Fences and walls are capped at 6 ft high and a satellite dish at 15 ft.
R-3 Residential - A two-family dwelling has no route in R-3. The residential uses are a single-family dwelling and, as an accessory use, a farm employee dwelling unit.
- The 20% coverage cap counts the house and all accessory structures together.
- A farm needs 5 acres on 300 ft of frontage, and agricultural pursuits, agricultural use structures and forestry uses 10 acres on 300 ft.
- By special permit, a stable or riding academy needs at least 10 acres and a veterinarian clinic or hospital at least 3 acres, each with 100 ft on all three yards.
- A home occupation is a special use too, and it needs a 50 ft rear yard rather than 25 ft.
- A silo is exempt from the height limit up to 90 ft.
- The 200 ft figure is frontage along the road, not width at the building line, where the ordinance sets no figure.
R-1 Residential - A duplex is a permitted principal use on the same acre, frontage and yards as a house, with ten more percentage points of coverage. It is also listed as a special permit use, so confirm with the Building Department whether a permit is needed.
- A duplex takes the same acre, frontage and yards with coverage rising from 20% to 30%.
- The 20% coverage cap counts the house and all accessory structures together.
- R-1 is purely residential, with no commercial, farm or agricultural use.
- A park or library, by special permit, needs one acre on 200 ft of frontage. A park takes 10 ft on all three yards and 20% coverage.
- The 150 ft figure is frontage along the road, not width at the building line, where the ordinance sets no figure.
- Fences and walls are capped at 6 ft high and a satellite dish at 15 ft.
MH Mobile Home - The figures shown are for a mobile home on an established lot in an established mobile home park, not for placing one on a new lot or creating a park. Creating or expanding a park needs a special permit and 5 acres.
- Creating or expanding the park itself needs 5 acres on 150 ft of frontage, with 50 ft front and 25 ft side and rear yards and only 10% coverage, a third of the individual lot's allowance.
- The 30% coverage cap counts the home and all accessory structures together.
- A private garage or storage shed needs only 5 ft side and rear yards, and a swimming pool or satellite dish 10 ft.
- By special permit, a laundromat or a quickstop retail food store needs 20,000 sq ft on 50 ft of frontage at 50% coverage, and the food store may not have gasoline pumps.
- Also by special permit, a park or recreation area needs at least one acre on 50 ft of frontage at 10% coverage.
- The 75 ft figure is frontage along the road, not width at the building line, where the ordinance sets no figure.
C/R Commercial/Residential - A single-family dwelling is the only permitted principal use. A duplex and every commercial use need a special permit, all on the same one acre and 150 ft of frontage, with coverage varying by use.
- Coverage is 30% for a duplex or library, and 50% for offices, a research and development centre, indoor commercial recreation, a restaurant, tavern, theatre or church.
- A church may be 70 ft tall and needs 30 ft side and rear yards rather than 25 ft.
- A park is held to 10% coverage and 10 ft on all three yards.
- Coverage counts the principal building and all accessory structures together.
- The 150 ft figure is frontage along the road, not width at the building line, where the ordinance sets no figure.
- Fences and walls are capped at 6 ft high and a satellite dish at 15 ft.
H Hamlet - A duplex is a permitted principal use here, but it needs 40,000 sq ft, double the 20,000 sq ft for a single-family dwelling, on the same frontage, the same yards and the same 50% coverage.
- The 50% coverage cap counts the house and all accessory structures together.
- Commercial uses, from retail and a restaurant to a professional office or pharmacy, take the same 20,000 sq ft but only 50 ft of frontage, and most rise to 60% coverage.
- An acre is needed for a public or semi-public use or library at 75 ft of frontage, a funeral home or bed-and-breakfast at 100, and a day-care centre, nursing home, school or church at 150.
- A hotel or motel needs two acres on 100 ft of frontage.
- A church may be 70 feet tall and a personal service establishment 40 feet, against the 35 ft that applies to every other use.
- The 100 ft figure is frontage along the road, not width at the building line, where the ordinance sets no figure.
I Industrial - Nothing may be built here without a special permit, because every use in the district is a special permit use. Adult businesses and commercial communications radio towers need only one acre but 50 ft side and rear yards and 25% coverage.
- Sawmills, a lumberyard, a truck terminal and mining need 3 acres, a recyclables handling and recovery facility 2 acres, and a composting facility 5 acres.
- The figures shown cover manufacturing, research and development centres, wholesale storage and trade, agribusiness, public utility use and warehousing.
- Coverage counts the principal building and all accessory structures together.
- The 200 ft figure is frontage along the road, not width at the building line, where the ordinance sets no figure.
Size limits on record in Northumberland
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 Northumberland:
- APD Agricultural ProtectionIn H a duplex needs 40,000 sq ft, double the 20,000 sq ft a single-family dwelling needs, so the second unit costs a full additional lot.
- R-3 ResidentialIn H a duplex needs 40,000 sq ft, double the 20,000 sq ft a single-family dwelling needs, so the second unit costs a full additional lot.
- R-1 ResidentialIn H a duplex needs 40,000 sq ft, double the 20,000 sq ft a single-family dwelling needs, so the second unit costs a full additional lot.
- MH Mobile HomeIn H a duplex needs 40,000 sq ft, double the 20,000 sq ft a single-family dwelling needs, so the second unit costs a full additional lot.
- C/R Commercial/ResidentialIn H a duplex needs 40,000 sq ft, double the 20,000 sq ft a single-family dwelling needs, so the second unit costs a full additional lot.
- H HamletIn H a duplex needs 40,000 sq ft, double the 20,000 sq ft a single-family dwelling needs, so the second unit costs a full additional lot.
- I IndustrialIn H a duplex needs 40,000 sq ft, double the 20,000 sq ft a single-family dwelling needs, so the second unit costs a full additional lot.
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 National Grid 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 Northumberland has no local short-term rental law, and that is not the same as permission. Confirm in writing with the Building Department before counting on short-stay income. Separate question from whether you can build the unit.
- Zoning codewww.northumberlandny.gov/zoning-planning
- Building dept(518) 792-9179
Sizing up a specific parcel in Northumberland?
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Building a full house instead?
A standard-finish house in Northumberland runs $204–268/sq ft, about $370k–480k at 1,800 sq ft , plus roughly $1,248 for a conforming lot. See what it costs to build a house in Northumberland.
ADU cost in nearby towns
All Saratoga County towns: Mechanicville (City) · Saratoga Springs (City) · Ballston · Charlton · Clifton Park · Corinth · Day · Edinburg · Galway · Greenfield · Halfmoon · Malta · Milton · Moreau · Providence · Saratoga · Stillwater · Waterford · Wilton · Ballston Spa (Village) · Corinth (Village) · Round Lake (Village) · Schuylerville (Village) · South Glens Falls (Village) · Stillwater (Village) · Victory (Village) · Waterford (Village)
More on Northumberland: Can you build an ADU here? · Zoning for new construction · Saratoga County build cost
ADU cost in Northumberland: common questions
How much does it cost to build an ADU in Northumberland, NY?
An 800 sq ft accessory dwelling unit in Town of Northumberland 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 Northumberland?
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 Northumberland?
Town of Northumberland has 7 districts. All districts prohibit ADUs. Check the specific address with the free ADU checker or confirm with the building department at (518) 792-9179 before you spend money on design.
Can I rent an ADU in Northumberland short term?
No local short-term-rental law on record - which is not the same as permission for Town of Northumberland. 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 Saratoga 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 Northumberland vary by district and often carry exceptions this page does not show; zoning last reviewed 2026-08-02; verify with the building department at (518) 792-9179 before relying on any answer. Sources: the Offsite / Aldo cost engine and zoning dataset.