Greenfield · ADU cost
What it costs to build an ADU in Greenfield, NY
An 800 sq ft accessory dwelling unit in Greenfield 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 Greenfield maps 7 districts that treat accessory units differently from one another, so read the table below as a starting point rather than a verdict.
ADU cost by size in Greenfield
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 Greenfield 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 |
|---|---|---|---|---|
| Low Density Residential District (a single-family dwelling on 4 ACRES WITH SEWER rising to 6 ACRES WITHOUT, 200/250 ft frontage, 75 ft front yard, 50 ft side, 75 ft rear, a 0.15 coverage ratio (15%) and 35 ft height. The area table states TWO minimum lot sizes per use, WITH SEWER and WITHOUT SEWER, and minLotSize records the with-sewer figure. Greenfield is largely unsewered, so the without-sewer column is the one that usually governs — check service before sizing anything. At six unsewered acres this is among the largest residential minimums in Saratoga County, and since Greenfield is a rural town in the Palmertown Range foothills with little public sewer, six acres is the realistic figure for most LDR land. COVERAGE IS STATED AS A RATIO, NOT A PERCENTAGE. Appendix E's column is headed 'Maximum Lot Coverage Ratio' and prints decimals — 0.15, 0.30, 0.5, 0.6, 0.05 — which maxLotCoverage stores as the equivalent integer percent. Read the decimal before converting: 0.5 is 50%, not 5%. The frontage column prints a PAIR (e.g. 200/250) rather than one number; the two figures distinguish lot configurations, so read Appendix E directly rather than assuming the lower one applies. Most non-residential uses share the identical 4/6-acre, 200/250 ft, 75-50-75, 0.15, 35 ft row — academic institutions, bed-and-breakfast, cemetery, community residence, family day care, garage apartment, in-law apartment, home occupation Type 1 and single mobile homes are all priced the same. The exceptions are the large ones: a CAMPGROUND and a KENNEL each need 10 ACRES (the kennel at 100 ft side and rear yards), a large contractor's storage yard 6 acres with 100 ft side and rear, a farmstand 6 acres, and home occupation Type 2 six acres with sewer or eight without. Agricultural uses and agricultural processing are the outlier in the other direction at 2 acres either way, with a 0.6 ratio and 50 ft height — a materially larger envelope than a house gets.) | 4 ac | 75 / 50 / 75 ft | 35 ft | As of right |
| Medium Density Residential 1 District (THE TOWN'S DENSEST RESIDENTIAL STANDARD: a single-family dwelling on 1 ACRE WITH SEWER or 1.5 ACRES WITHOUT, 100/150 ft frontage, 40 ft front yard, 25 ft side, 50 ft rear, a 0.30 coverage ratio (30%) and 35 ft height. Against LDR that is a quarter of the lot, half the front yard, half the side yard and double the coverage — MDR1 is where Greenfield's conventional residential development actually happens. The area table states TWO minimum lot sizes per use, WITH SEWER and WITHOUT SEWER, and minLotSize records the with-sewer figure. Greenfield is largely unsewered, so the without-sewer column is the one that usually governs — check service before sizing anything. COVERAGE IS STATED AS A RATIO, NOT A PERCENTAGE. Appendix E's column is headed 'Maximum Lot Coverage Ratio' and prints decimals — 0.15, 0.30, 0.5, 0.6, 0.05 — which maxLotCoverage stores as the equivalent integer percent. Read the decimal before converting: 0.5 is 50%, not 5%. The frontage column prints a PAIR (e.g. 200/250) rather than one number; the two figures distinguish lot configurations, so read Appendix E directly rather than assuming the lower one applies. The garage apartment and in-law apartment rows sit at 2 acres with sewer / 3 without at 200/300 ft frontage, so an accessory unit here requires DOUBLE the land of the principal dwelling — a significant and easily missed cost. Agricultural uses and agricultural processing move to a special use permit in MDR1 where they are site-plan-review in LDR, which is the clearest signal of the district's more suburban intent.) | 1 ac | 40 / 25 / 50 ft | 35 ft | As of right |
| Medium Density Residential 2 District (a single-family dwelling on 2 ACRES WITH SEWER or 3 ACRES WITHOUT, 150/200 ft frontage, 75 ft front yard, 35 ft side, 75 ft rear, a 0.15 coverage ratio (15%) and 35 ft height. DESPITE THE NAME, MDR2 IS CLOSER TO LDR THAN TO MDR1: it shares LDR's 75 ft front and rear yards and its 0.15 coverage ratio, and only the lot size and side yard sit between the two. Anyone reading MDR1 and MDR2 as a matched pair will overstate what MDR2 allows — the coverage ratio is HALF MDR1's and the front yard nearly double. The area table states TWO minimum lot sizes per use, WITH SEWER and WITHOUT SEWER, and minLotSize records the with-sewer figure. Greenfield is largely unsewered, so the without-sewer column is the one that usually governs — check service before sizing anything. COVERAGE IS STATED AS A RATIO, NOT A PERCENTAGE. Appendix E's column is headed 'Maximum Lot Coverage Ratio' and prints decimals — 0.15, 0.30, 0.5, 0.6, 0.05 — which maxLotCoverage stores as the equivalent integer percent. Read the decimal before converting: 0.5 is 50%, not 5%. The frontage column prints a PAIR (e.g. 200/250) rather than one number; the two figures distinguish lot configurations, so read Appendix E directly rather than assuming the lower one applies. Garage and in-law apartments take 2 acres with sewer / 3 without at 150/200 ft frontage, matching the principal dwelling rather than doubling it as MDR1 requires — so an accessory unit is materially cheaper in land here than one district over.) | 2 ac | 75 / 35 / 75 ft | 35 ft | As of right |
| Town Center District (the village-scale core and, with Office Residential, the only place Greenfield permits an urban form: a single-family dwelling on 1 ACRE WITH SEWER or 2 ACRES WITHOUT, 75/120 ft frontage, a 45 ft front yard, 10 FT ONE SIDE / 25 FT BOTH SIDES, only a 15 FT REAR YARD, a 0.5 coverage ratio (50%) and 50 FT HEIGHT. The area table states TWO minimum lot sizes per use, WITH SEWER and WITHOUT SEWER, and minLotSize records the with-sewer figure. Greenfield is largely unsewered, so the without-sewer column is the one that usually governs — check service before sizing anything. THE SIDE YARD IS A PAIR AND BOTH FIGURES BIND — 10 ft on any one side and 25 ft for the two combined, so two 10 ft side yards are not compliant and the second must be at least 15 ft. THE 15 FT REAR YARD IS THE SHALLOWEST IN THE TOWN by a wide margin, against 50 ft in MDR1 and 75 ft in LDR and MDR2, and together with the 50% coverage and 50 ft height it is what makes TC the only district where a genuinely compact building is possible. COVERAGE IS STATED AS A RATIO, NOT A PERCENTAGE. Appendix E's column is headed 'Maximum Lot Coverage Ratio' and prints decimals — 0.15, 0.30, 0.5, 0.6, 0.05 — which maxLotCoverage stores as the equivalent integer percent. Read the decimal before converting: 0.5 is 50%, not 5%. The frontage column prints a PAIR (e.g. 200/250) rather than one number; the two figures distinguish lot configurations, so read Appendix E directly rather than assuming the lower one applies. Garage and in-law apartments take the same 1/2-acre, 75/120 ft, 45 ft, 10-one/25, 15 ft, 0.5, 50 ft row as the principal dwelling, so an accessory unit costs no additional land here at all — the most permissive accessory-unit economics in the Town.) | 1 ac | 45 / 10 / 15 ft | 50 ft | As of right |
| Office Residential District (DIMENSIONALLY IDENTICAL TO TOWN CENTER in every column — 1 acre with sewer / 2 acres without, 75/120 ft frontage, 45 ft front, 10 ft one side / 25 ft both, 15 ft rear, 0.5 coverage ratio (50%), 50 ft height — so the two districts differ entirely in permitted USE rather than in envelope, OR admitting professional office activity alongside housing. The area table states TWO minimum lot sizes per use, WITH SEWER and WITHOUT SEWER, and minLotSize records the with-sewer figure. Greenfield is largely unsewered, so the without-sewer column is the one that usually governs — check service before sizing anything. COVERAGE IS STATED AS A RATIO, NOT A PERCENTAGE. Appendix E's column is headed 'Maximum Lot Coverage Ratio' and prints decimals — 0.15, 0.30, 0.5, 0.6, 0.05 — which maxLotCoverage stores as the equivalent integer percent. Read the decimal before converting: 0.5 is 50%, not 5%. ON THE ACCESSORY DWELLING, OR AND TC ARE IDENTICAL AS WELL: Appendix D lists the in-law apartment as PA and the garage apartment as SUP in both. The side yard is a pair and both figures bind, as in TC.) | 1 ac | 45 / 10 / 15 ft | 50 ft | As of right |
| Industrial Manufacturing District (2 ACRES with or without sewer — the only district where the sewer ladder collapses to a single figure — with 200 ft frontage, 50 ft front yard, 25 ft side, 40 ft rear, a 0.6 coverage ratio (60%, the highest in the Town) and 50 ft height. Nearly every IM use shares that identical row: academic institutions, boardinghouse, contractor's storage yard, home occupation Type 1, hospitals and institutions for the handicapped, and hotel, inn or motel. THE SINGLE-FAMILY DWELLING IS 'n/a' IN IM — NOT ALLOWED — which makes this the only Greenfield district with no by-right housing at all. The in-law apartment IS listed at the same 2-acre row, which is an oddity given there is no principal dwelling to be accessory to; § 105-7 defines it as contained within a single-family detached structure, so the listing presumably attaches to a boardinghouse or similar and is worth confirming before relying on it. COVERAGE IS STATED AS A RATIO, NOT A PERCENTAGE. Appendix E's column is headed 'Maximum Lot Coverage Ratio' and prints decimals — 0.15, 0.30, 0.5, 0.6, 0.05 — which maxLotCoverage stores as the equivalent integer percent. Read the decimal before converting: 0.5 is 50%, not 5%.) | 2 ac | 50 / 25 / 40 ft | 50 ft | As of right |
| That is not a typo — the figure is stated identically for both the with-sewer and without-sewer columns, and the garage and in-law apartment rows repeat it at 42.7 acres with 800 ft of frontage. THE PRACTICAL EFFECT IS THAT PR LAND IS NOT RESIDENTIALLY DEVELOPABLE at any ordinary parcel size: 42.7 acres is roughly seven times the largest requirement anywhere else in Greenfield and about 65 times the MDR1 serviced minimum, and the 5% coverage ratio caps a 42.7-acre lot's buildings at about 93,000 sf spread across the whole parcel. Treat PR as conservation and recreation land with a theoretical single homesite rather than as acreage to underwrite. Adult uses are the one activity PR uniquely permits (by special use permit), available in no other Greenfield district. COVERAGE IS STATED AS A RATIO, NOT A PERCENTAGE. Appendix E's column is headed 'Maximum Lot Coverage Ratio' and prints decimals — 0.15, 0.30, 0.5, 0.6, 0.05 — which maxLotCoverage stores as the equivalent integer percent. Read the decimal before converting: 0.5 is 50%, not 5%.) | 42.7 ac | 150 / 100 / 150 ft | 35 ft | As of right |
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Size limits on record in Greenfield
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 Greenfield:
- Low Density Residential District (a single-family dwelling on 4 ACRES WITH SEWER rising to 6 ACRES WITHOUT, 200/250 ft frontage, 75 ft front yard, 50 ft side, 75 ft rear, a 0.15 coverage ratio (15%) and 35 ft height. The area table states TWO minimum lot sizes per use, WITH SEWER and WITHOUT SEWER, and minLotSize records the with-sewer figure. Greenfield is largely unsewered, so the without-sewer column is the one that usually governs — check service before sizing anything. At six unsewered acres this is among the largest residential minimums in Saratoga County, and since Greenfield is a rural town in the Palmertown Range foothills with little public sewer, six acres is the realistic figure for most LDR land. COVERAGE IS STATED AS A RATIO, NOT A PERCENTAGE. Appendix E's column is headed 'Maximum Lot Coverage Ratio' and prints decimals — 0.15, 0.30, 0.5, 0.6, 0.05 — which maxLotCoverage stores as the equivalent integer percent. Read the decimal before converting: 0.5 is 50%, not 5%. The frontage column prints a PAIR (e.g. 200/250) rather than one number; the two figures distinguish lot configurations, so read Appendix E directly rather than assuming the lower one applies. Most non-residential uses share the identical 4/6-acre, 200/250 ft, 75-50-75, 0.15, 35 ft row — academic institutions, bed-and-breakfast, cemetery, community residence, family day care, garage apartment, in-law apartment, home occupation Type 1 and single mobile homes are all priced the same. The exceptions are the large ones: a CAMPGROUND and a KENNEL each need 10 ACRES (the kennel at 100 ft side and rear yards), a large contractor's storage yard 6 acres with 100 ft side and rear, a farmstand 6 acres, and home occupation Type 2 six acres with sewer or eight without. Agricultural uses and agricultural processing are the outlier in the other direction at 2 acres either way, with a 0.6 ratio and 50 ft height — a materially larger envelope than a house gets.)Maximum 1,000 sq ft and no more than 40% of the principal building's gross floor area, one per lot, septic verified by a licensed PE
- Medium Density Residential 1 District (THE TOWN'S DENSEST RESIDENTIAL STANDARD: a single-family dwelling on 1 ACRE WITH SEWER or 1.5 ACRES WITHOUT, 100/150 ft frontage, 40 ft front yard, 25 ft side, 50 ft rear, a 0.30 coverage ratio (30%) and 35 ft height. Against LDR that is a quarter of the lot, half the front yard, half the side yard and double the coverage — MDR1 is where Greenfield's conventional residential development actually happens. The area table states TWO minimum lot sizes per use, WITH SEWER and WITHOUT SEWER, and minLotSize records the with-sewer figure. Greenfield is largely unsewered, so the without-sewer column is the one that usually governs — check service before sizing anything. COVERAGE IS STATED AS A RATIO, NOT A PERCENTAGE. Appendix E's column is headed 'Maximum Lot Coverage Ratio' and prints decimals — 0.15, 0.30, 0.5, 0.6, 0.05 — which maxLotCoverage stores as the equivalent integer percent. Read the decimal before converting: 0.5 is 50%, not 5%. The frontage column prints a PAIR (e.g. 200/250) rather than one number; the two figures distinguish lot configurations, so read Appendix E directly rather than assuming the lower one applies. The garage apartment and in-law apartment rows sit at 2 acres with sewer / 3 without at 200/300 ft frontage, so an accessory unit here requires DOUBLE the land of the principal dwelling — a significant and easily missed cost. Agricultural uses and agricultural processing move to a special use permit in MDR1 where they are site-plan-review in LDR, which is the clearest signal of the district's more suburban intent.)Maximum 1,000 sq ft and no more than 40% of the principal building's gross floor area, one per lot, septic verified by a licensed PE
- Medium Density Residential 2 District (a single-family dwelling on 2 ACRES WITH SEWER or 3 ACRES WITHOUT, 150/200 ft frontage, 75 ft front yard, 35 ft side, 75 ft rear, a 0.15 coverage ratio (15%) and 35 ft height. DESPITE THE NAME, MDR2 IS CLOSER TO LDR THAN TO MDR1: it shares LDR's 75 ft front and rear yards and its 0.15 coverage ratio, and only the lot size and side yard sit between the two. Anyone reading MDR1 and MDR2 as a matched pair will overstate what MDR2 allows — the coverage ratio is HALF MDR1's and the front yard nearly double. The area table states TWO minimum lot sizes per use, WITH SEWER and WITHOUT SEWER, and minLotSize records the with-sewer figure. Greenfield is largely unsewered, so the without-sewer column is the one that usually governs — check service before sizing anything. COVERAGE IS STATED AS A RATIO, NOT A PERCENTAGE. Appendix E's column is headed 'Maximum Lot Coverage Ratio' and prints decimals — 0.15, 0.30, 0.5, 0.6, 0.05 — which maxLotCoverage stores as the equivalent integer percent. Read the decimal before converting: 0.5 is 50%, not 5%. The frontage column prints a PAIR (e.g. 200/250) rather than one number; the two figures distinguish lot configurations, so read Appendix E directly rather than assuming the lower one applies. Garage and in-law apartments take 2 acres with sewer / 3 without at 150/200 ft frontage, matching the principal dwelling rather than doubling it as MDR1 requires — so an accessory unit is materially cheaper in land here than one district over.)Maximum 1,000 sq ft and no more than 40% of the principal building's gross floor area, one per lot, septic verified by a licensed PE
- Town Center District (the village-scale core and, with Office Residential, the only place Greenfield permits an urban form: a single-family dwelling on 1 ACRE WITH SEWER or 2 ACRES WITHOUT, 75/120 ft frontage, a 45 ft front yard, 10 FT ONE SIDE / 25 FT BOTH SIDES, only a 15 FT REAR YARD, a 0.5 coverage ratio (50%) and 50 FT HEIGHT. The area table states TWO minimum lot sizes per use, WITH SEWER and WITHOUT SEWER, and minLotSize records the with-sewer figure. Greenfield is largely unsewered, so the without-sewer column is the one that usually governs — check service before sizing anything. THE SIDE YARD IS A PAIR AND BOTH FIGURES BIND — 10 ft on any one side and 25 ft for the two combined, so two 10 ft side yards are not compliant and the second must be at least 15 ft. THE 15 FT REAR YARD IS THE SHALLOWEST IN THE TOWN by a wide margin, against 50 ft in MDR1 and 75 ft in LDR and MDR2, and together with the 50% coverage and 50 ft height it is what makes TC the only district where a genuinely compact building is possible. COVERAGE IS STATED AS A RATIO, NOT A PERCENTAGE. Appendix E's column is headed 'Maximum Lot Coverage Ratio' and prints decimals — 0.15, 0.30, 0.5, 0.6, 0.05 — which maxLotCoverage stores as the equivalent integer percent. Read the decimal before converting: 0.5 is 50%, not 5%. The frontage column prints a PAIR (e.g. 200/250) rather than one number; the two figures distinguish lot configurations, so read Appendix E directly rather than assuming the lower one applies. Garage and in-law apartments take the same 1/2-acre, 75/120 ft, 45 ft, 10-one/25, 15 ft, 0.5, 50 ft row as the principal dwelling, so an accessory unit costs no additional land here at all — the most permissive accessory-unit economics in the Town.)Maximum 1,000 sq ft and no more than 40% of the principal building's gross floor area, one per lot, septic verified by a licensed PE
- Office Residential District (DIMENSIONALLY IDENTICAL TO TOWN CENTER in every column — 1 acre with sewer / 2 acres without, 75/120 ft frontage, 45 ft front, 10 ft one side / 25 ft both, 15 ft rear, 0.5 coverage ratio (50%), 50 ft height — so the two districts differ entirely in permitted USE rather than in envelope, OR admitting professional office activity alongside housing. The area table states TWO minimum lot sizes per use, WITH SEWER and WITHOUT SEWER, and minLotSize records the with-sewer figure. Greenfield is largely unsewered, so the without-sewer column is the one that usually governs — check service before sizing anything. COVERAGE IS STATED AS A RATIO, NOT A PERCENTAGE. Appendix E's column is headed 'Maximum Lot Coverage Ratio' and prints decimals — 0.15, 0.30, 0.5, 0.6, 0.05 — which maxLotCoverage stores as the equivalent integer percent. Read the decimal before converting: 0.5 is 50%, not 5%. ON THE ACCESSORY DWELLING, OR AND TC ARE IDENTICAL AS WELL: Appendix D lists the in-law apartment as PA and the garage apartment as SUP in both. The side yard is a pair and both figures bind, as in TC.)Maximum 1,000 sq ft and no more than 40% of the principal building's gross floor area, one per lot, septic verified by a licensed PE
- Industrial Manufacturing District (2 ACRES with or without sewer — the only district where the sewer ladder collapses to a single figure — with 200 ft frontage, 50 ft front yard, 25 ft side, 40 ft rear, a 0.6 coverage ratio (60%, the highest in the Town) and 50 ft height. Nearly every IM use shares that identical row: academic institutions, boardinghouse, contractor's storage yard, home occupation Type 1, hospitals and institutions for the handicapped, and hotel, inn or motel. THE SINGLE-FAMILY DWELLING IS 'n/a' IN IM — NOT ALLOWED — which makes this the only Greenfield district with no by-right housing at all. The in-law apartment IS listed at the same 2-acre row, which is an oddity given there is no principal dwelling to be accessory to; § 105-7 defines it as contained within a single-family detached structure, so the listing presumably attaches to a boardinghouse or similar and is worth confirming before relying on it. COVERAGE IS STATED AS A RATIO, NOT A PERCENTAGE. Appendix E's column is headed 'Maximum Lot Coverage Ratio' and prints decimals — 0.15, 0.30, 0.5, 0.6, 0.05 — which maxLotCoverage stores as the equivalent integer percent. Read the decimal before converting: 0.5 is 50%, not 5%.)Maximum 1,000 sq ft and no more than 40% of the principal building's gross floor area, one per lot, septic verified by a licensed PE
- That is not a typo — the figure is stated identically for both the with-sewer and without-sewer columns, and the garage and in-law apartment rows repeat it at 42.7 acres with 800 ft of frontage. THE PRACTICAL EFFECT IS THAT PR LAND IS NOT RESIDENTIALLY DEVELOPABLE at any ordinary parcel size: 42.7 acres is roughly seven times the largest requirement anywhere else in Greenfield and about 65 times the MDR1 serviced minimum, and the 5% coverage ratio caps a 42.7-acre lot's buildings at about 93,000 sf spread across the whole parcel. Treat PR as conservation and recreation land with a theoretical single homesite rather than as acreage to underwrite. Adult uses are the one activity PR uniquely permits (by special use permit), available in no other Greenfield district. COVERAGE IS STATED AS A RATIO, NOT A PERCENTAGE. Appendix E's column is headed 'Maximum Lot Coverage Ratio' and prints decimals — 0.15, 0.30, 0.5, 0.6, 0.05 — which maxLotCoverage stores as the equivalent integer percent. Read the decimal before converting: 0.5 is 50%, not 5%.)Maximum 1,000 sq ft and no more than 40% of the principal building's gross floor area, one per lot, septic verified by a licensed PE
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. No short-term-rental provision exists in the Town of Greenfield Zoning Law. Chapter 105 defines no short-term rental, vacation rental or transient-occupancy use, and Appendix D Table 1 Use Regulations lists none. There is no registration or licensing requirement in the chapter. THE ENUMERATED SHORT-STAY USES ARE THREE AND ALL ARE PERMIT-GATED, which is more than most Saratoga towns offer: BED-AND-BREAKFAST, HOTEL/INN/MOTEL, and CAMPGROUND, the last requiring 10 ACRES in Low Density Residential. Table 1 uses an explicit five-value key — PP (principal permitted use), SPR (permitted subject to site plan review), SUP (permitted subject to special use permit), PA (permitted as accessory to a principal use) and n/a (use not allowed) — so a use marked n/a is affirmatively prohibited and a use absent from the table has no route at all. Recorded 'unknown' rather than 'prohibited' because the Town has never legislated on short-term rental specifically, and whole-house rental of a permitted single-family dwelling is arguably the residential use itself. Absence of a found STR provision is NOT permission. Greenfield sits in the Palmertown Range foothills between Saratoga Springs and the southern Adirondacks, so short-stay demand is real — get a written answer from the Building Department at (518) 893-7432 x304 before underwriting it. Separately, New York State has required every short-term-rental host to register the unit with the State through the county registry since 2025, regardless of what the municipality allows, and Saratoga County HAS adopted a county-level short-term-rental programme: a 3% occupancy tax and a MANDATORY county registry, covering any room or space in a dwelling let for under 30 consecutive days. Registration runs two years, an unregistered host faces fines of up to $500, and the booking platform is separately liable for processing an unregistered listing — so Airbnb and Vrbo will delist. The City of Saratoga Springs runs its own registry alongside it. Separate question from whether you can build the unit.
- Building dept(518) 893-7432 x304
Sizing up a specific parcel in Greenfield?
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Building a full house instead?
A standard-finish house in Greenfield runs $204–268/sq ft, about $370k–480k at 1,800 sq ft , plus roughly $11,358 for a conforming lot. See what it costs to build a house in Greenfield.
ADU cost in nearby towns
Mechanicville (City)
800 sq ft ≈ $200k–260k
Saratoga Springs (City)
800 sq ft ≈ $200k–260k
Ballston
800 sq ft ≈ $200k–260k
Charlton
800 sq ft ≈ $200k–260k
Clifton Park
800 sq ft ≈ $200k–260k
Corinth
800 sq ft ≈ $200k–260k
All Saratoga County towns: Mechanicville (City) · Saratoga Springs (City) · Ballston · Charlton · Clifton Park · Corinth · Day · Edinburg · Galway · Halfmoon · Malta · Milton · Moreau · Northumberland · 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 Greenfield: Can you build an ADU here? · Zoning for new construction · Saratoga County build cost
ADU cost in Greenfield: common questions
How much does it cost to build an ADU in Greenfield, NY?
An 800 sq ft accessory dwelling unit in Town of Greenfield 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 Greenfield?
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 Greenfield?
Town of Greenfield has 7 districts. All districts allow ADUs. Check the specific address with the free ADU checker or confirm with the building department at (518) 893-7432 x304 before you spend money on design.
Can I rent an ADU in Greenfield short term?
No local short-term-rental law on record - which is not the same as permission for Town of Greenfield. 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 Greenfield vary by district and often carry exceptions this page does not show; zoning last reviewed 2026-07-31; verify with the building department at (518) 893-7432 x304 before relying on any answer. Sources: Offsite / Aldo cost engine (costEngine.js + constants.js); zoning dataset (municipalData.js).