Knox · ADU cost
What it costs to build an ADU in Knox, NY
An 800 sq ft accessory dwelling unit in Knox runs roughly $195k–260k, or about $247–323/sq ft, and that per-square-foot figure sits deliberately above the $202–265/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 Knox maps 9 districts that treat accessory units differently from one another, so read the table below as a starting point rather than a verdict.
Check a specific parcel for an ADU in Aldo, free →
ADU cost by size in Knox
Standard finish, slab on grade, on a flat and clear part of the lot, general-contractor margin included. These are structure costs at Albany County pricing, before the service and septic work a second dwelling can trigger.
| Size | Type | $ / sq ft | Estimated total |
|---|---|---|---|
| 400 sq ft | Studio | $327–$428 | $130k–170k |
| 600 sq ft | One bedroom | $273–$358 | $165k–215k |
| 800 sq ft | One bedroom, larger | $247–$323 | $195k–260k |
| 1,000 sq ft | Two bedroom | $231–$302 | $230k–300k |
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 | $27–$33 | $16 | 55% |
| Electrical | $18–$23 | $13 | 35% |
| HVAC | $23–$28 | $14 | 45% |
| Insulation | $7–$9 | $7 | — |
| Interior finishes | $32–$43 | $27 | 15% |
| Millwork & cabinetry | $18–$27 | $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 Knox 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 | 3 ac | 75 / 50 / 50 ft | 35 ft | No |
| Ag & Mining | 3 ac | 75 / 50 / 50 ft | 35 ft | No |
| Multi-Use & B1 | 3 ac | 75 / - / 30 ft | 35 ft | No |
| Multi_Use and Agricultural | — | — | — | No |
| Land Conservation 1 | 3 ac | 75 / 50 / 50 ft | 35 ft | No |
| Land Conservation 2 | 3 ac | 75 / 50 / 50 ft | 35 ft | No |
| Residential | 3 ac | 75 / 50 / 50 ft | 35 ft | No |
| Residential/Recreational | — | — | — | — |
| Multi-Use Recreational | 3 ac | 75 / - / - ft | 35 ft | No |
Agricultural, Ag & Mining - The three acre minimum is per family, not per lot, so a two-family dwelling needs six acres and the figure scales with the unit count. The 25% coverage cap includes accessory buildings.
- A nonresidential use needs ten acres and 400 ft of frontage, and a recreational facility 50 acres.
- Where a side or rear yard adjoins a street, the front yard standard applies to it under § 52C.
- Yards are measured from the foundation under § 52G.
- Cluster development under § 50O and multiple dwellings under § 50K change the lot requirement.
Multi-Use & B1 - No side yard is required here except where the lot abuts property in residential use. A side yard that is then provided must be at least 12.5 ft, and where the lot abuts a residential district at least 100 ft.
- The three acre minimum is per family, not per lot, so a two-family dwelling needs six acres.
- A nonresidential use needs the same three acres, on 200 ft of frontage rather than 250 ft.
- This district reaches three storeys, and no minimum living space is published.
- Where a side or rear yard adjoins a street, the front yard standard applies to it under § 52C.
- Yards are measured from the foundation under § 52G.
- Cluster development under § 50O and multiple dwellings under § 50K change the lot requirement.
Multi_Use and Agricultural - No district of this name appears in the zoning ordinance, so it carries no dimensional standard of its own. The label reads as two district names run together, the way a parcel with split zoning is shown, so resolve the parcel to its actual district on the Town Zoning Map.
Land Conservation 1, Land Conservation 2 - The Density Control Schedule leaves this district's row entirely blank. The figures shown match the row printed directly above it, so they may carry down or the town may publish no dimensional standard here: confirm them with the town before relying on them.
- Where a side or rear yard adjoins a street, the front yard standard applies to it (§ 52C).
- Yards are measured from the foundation (§ 52G).
Residential - The three acre minimum is per family, not per lot, so a two-family dwelling needs six acres and the figure scales with the unit count. The 25% coverage cap includes accessory buildings.
- A nonresidential use needs fifteen acres and 400 ft of frontage, five times what a dwelling needs, and a recreational facility needs 50 acres.
- Where a side or rear yard adjoins a street, the front yard standard applies to it under § 52C.
- Yards are measured from the foundation under § 52G.
- Cluster development under § 50O and multiple dwellings under § 50K change the lot requirement.
Residential/Recreational - The ordinance sets no dimensional standard for this district at all: it has no row in the Density Control Schedule. § 30(6) establishes it for seasonal dwellings on smaller lots than the town's other residential areas, but never says how much smaller, so confirm with the town.
Multi-Use Recreational - This district publishes neither a side nor a rear yard standard. The three acre minimum is also per family, not per lot, so a two-family dwelling needs six acres.
- A nonresidential use needs the same three acres, on 200 ft of frontage rather than 250 ft.
- The 30% coverage cap includes accessory buildings.
- Yards are measured from the foundation under § 52G.
- Cluster development under § 50O and multiple dwellings under § 50K change the lot requirement.
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 Knox has no local short-term rental law, and that is not permission. Confirm with the town before counting on renting a house short term. Separate question from whether you can build the unit.
- Zoning codewww.knoxny.gov/buildingzoning-department.html
- Building dept(518) 872-2551
Sizing up a specific parcel in Knox?
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 Knox runs $202–265/sq ft, about $365k–475k at 1,800 sq ft , plus roughly $14,100 for a conforming lot. See what it costs to build a house in Knox.
ADU cost in nearby towns
All Albany County towns: Albany (City) · Cohoes (City) · Watervliet (City) · Berne · Bethlehem · Coeymans · Colonie · Guilderland · New Scotland · Rensselaerville · Westerlo · Altamont (Village) · Colonie (Village) · Green Island (Village) · Menands (Village) · Ravena (Village) · Voorheesville (Village)
More on Knox: Can you build an ADU here? · Zoning for new construction · Albany County build cost
ADU cost in Knox: common questions
How much does it cost to build an ADU in Knox, NY?
An 800 sq ft accessory dwelling unit in Town of Knox runs roughly $195k–260k at a standard finish, general-contractor margin included. A 400 sq ft studio runs about $130k–170k. 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 Knox?
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 $247–323/sq ft against $202–265/sq ft for a full house, even though it is the same trades doing the same work.
Are ADUs allowed in Knox?
Town of Knox has 9 districts. 8 of 9 districts prohibit ADUs. 1 district has incomplete data - verify with the building department at (518) 872-2551. Check the specific address with the free ADU checker before you spend money on design.
Can I rent an ADU in Knox short term?
No local short-term-rental law on record - which is not the same as permission for Town of Knox. 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 Albany 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 Knox vary by district and often carry exceptions this page does not show; zoning last reviewed 2026-09-19; verify with the building department at (518) 872-2551 before relying on any answer. Sources: the Offsite / Aldo cost engine and zoning dataset.