Franklin · ADU cost
What it costs to build an ADU in Franklin, NY
An 800 sq ft accessory dwelling unit in Franklin runs roughly $185k–245k, or about $233–305/sq ft, and that per-square-foot figure sits deliberately above the $191–250/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 Franklin maps 6 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 Franklin
Standard finish, slab on grade, on a flat and clear part of the lot, general-contractor margin included. These are structure costs at Delaware County pricing, before the service and septic work a second dwelling can trigger.
| Size | Type | $ / sq ft | Estimated total |
|---|---|---|---|
| 400 sq ft | Studio | $309–$404 | $125k–160k |
| 600 sq ft | One bedroom | $258–$338 | $155k–205k |
| 800 sq ft | One bedroom, larger | $233–$305 | $185k–245k |
| 1,000 sq ft | Two bedroom | $218–$285 | $220k–285k |
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–$10 | $7 | — |
| Foundation | $15–$21 | $15 | — |
| Framing | $24–$30 | $24 | — |
| Envelope - roof, siding, windows | $30–$38 | $30 | — |
| Plumbing | $26–$32 | $15 | 55% |
| Electrical | $17–$22 | $12 | 35% |
| HVAC | $21–$27 | $14 | 45% |
| Insulation | $7–$9 | $7 | — |
| Interior finishes | $30–$40 | $26 | 15% |
| Millwork & cabinetry | $17–$26 | $10 | 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 Franklin 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 I | 1 ac | 75 / 20 / 20 ft | 35 ft | Occupancy restricted |
| Rural III | 3 ac | 50 / 25 / 25 ft | 35 ft | Occupancy restricted |
| Rural V | 5 ac | 50 / 30 / 30 ft | 35 ft | Occupancy restricted |
| Hamlet | 0.5 ac | 30 / 20 / 20 ft | 35 ft | Occupancy restricted |
| Public Water Supply | 10 ac | 200 / 30 / 30 ft | 35 ft | Special permit |
| Development Limitations Overlay | — | — | — | Special permit |
Rural I - The 25 percent coverage cap is an impervious surface limit counting buildings and off street parking areas, not just the building footprint (§ 202). The front setback is stated from the road centre line, and the 75 ft shown is its lot line equivalent on a fifty foot right of way.
- On a narrower right of way the centre line rule binds harder: a 33 foot right of way puts the building about 58.5 ft back from the lot line, so measure the right of way before siting.
- Lot shape is capped at a 4:1 depth to width ratio, and for each increment in that ratio the required frontage extends by 50 ft.
- Land within 500 feet of the centre line of a state or county highway, with direct frontage on the right of way, falls in the highway corridor, which is intended for mixed uses (§ 404A).
- Where the Development Limitations Overlay covers more than half of a parcel being subdivided, a lots per acre cap takes over from the lot minimum.
- Lot size averaging cannot bring a lot below the one acre floor set by § 411.
Rural III - Rural III applies to land within 500 feet of the centre line of a town road with direct frontage, counting roads the Town maintained as of the ordinance's effective date and excluding seasonal use roads. A parcel on a seasonal road falls to Rural V, at five acres.
- Whether a road counts as maintained or as seasonal use is not something a map shows, so confirm the road's status with the Town.
- Lot size averaging under § 411 can reach a one-acre lot only if all lots proposed average at least three acres and undersized lots are no more than 20% of the total proposed.
- Averaging also requires a buildable and accessible site on every lot, septic and well separation satisfying the State Health Department, and one dwelling unit per district minimum lot size.
- Averaging may be used only once every twenty years per original subdivision.
- The coverage percentage is an impervious surface cap under § 202, counting buildings and off-street parking areas, not just a building footprint, so driveway and parking take a real share.
- The code measures the front setback from the road centre line; the figure shown is the lot-line equivalent on a fifty-foot right-of-way. A 33-foot right-of-way puts it about 58.5 ft back.
Rural V - The 15% coverage cap counts all impervious surface, including driveways and off-street parking, not just buildings. The ordinance also states the cap in words as fifteen per cent but in numerals as 25%, so confirm it with the town before relying on either reading.
- Subdivision lot size averaging under § 411 can create lots as small as one acre, provided the average of all lots proposed is at least five acres in Rural V.
- Averaging is limited: undersized lots may be no more than 20% of the total lots proposed, and it may be used only once every twenty years per original subdivision.
- Every lot must have a buildable and accessible site, septic and well separation must satisfy the State Health Department, and there is one dwelling unit per district minimum lot size.
- The front setback is stated from the road centre line, so a narrower right-of-way binds harder: a 33-foot right-of-way pushes the building about 58.5 ft back from the lot line.
- A maximum lot depth-to-width ratio of 4:1 applies.
- Where the Development Limitations Overlay covers more than half the parcel being subdivided, a lots-per-acre cap takes over from the lot minimum.
Hamlet - The 25% coverage cap is an impervious surface limit under § 202, counting buildings plus off-street parking and driveways, so paving eats into what you can build. Front setback is set as 55 ft from the road centre line, which on a fifty-foot right-of-way gives the 30 ft shown.
- Lots here follow a 3:1 depth-to-width ratio, tighter than the 4:1 used elsewhere in the town.
- Where the Development Limitations Overlay covers more than half of a parcel being subdivided, a lots-per-acre cap governs instead of the lot minimum; see DL (Development Limitations Overlay).
- Lot size averaging under § 411 starts at a one acre floor, so it offers nothing at this district's half-acre minimum.
- This district covers the hamlet of Treadwell as shown on the zoning map. The Village of Franklin is a separate jurisdiction, and these figures do not answer for a village parcel.
Public Water Supply - Nothing is allowed here without a special permit, including a one- or two-family dwelling. The district covers all land within a 500-foot radius of the public water supply wells and springs serving the Village of Franklin and the hamlet of Treadwell.
- Special permit uses include one one- or two-family dwelling per lot, one mobile home per lot, agriculture, forest and wildlife management, public utilities, and public parks and recreation.
- The 10% coverage cap is an impervious surface limit under § 202, counting buildings and off-street parking areas, so driveways and parking use up part of it.
- Accessory uses are those listed for Rural I, and they also require a special permit.
- The 200 ft front setback is measured from the right-of-way under § 408F(4).
- A maximum lot depth-to-width ratio of 4:1 applies.
Development Limitations Overlay - This overlay sits over another district and uses that district's dimensional standards. The one change is yield: where more than fifty percent of the original parcel being subdivided lies in Development Limitations, the number of lots per acre is capped.
- Above that threshold, the maximum number of lots per acre of the original parcel is 0.44 in Rural I, 0.15 in Rural III and 0.09 in Rural V (§ 409D(1)).
- Below that threshold the overlay changes nothing.
- The cap is applied to the original parcel being subdivided, not to each lot created.
- Minimum lot size, minimum frontage, maximum height, front, side and rear setbacks, maximum lot coverage and the depth-to-width ratio are all the same as the underlying district (§ 409D).
Size limits on record in Franklin
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 Franklin:
- Rural I§ 512 requires 800 square feet of habitable floor area for one- and two-family dwellings.
- Rural III§ 512 requires 800 square feet of habitable floor area for one- and two-family dwellings.
- Rural V§ 512 requires 800 square feet of habitable floor area for one- and two-family dwellings.
- Hamlet§ 512 requires 800 square feet of habitable floor area for one- and two-family dwellings.
- Public Water Supply§ 512 requires 800 square feet of habitable floor area for one- and two-family dwellings.
- Development Limitations Overlay§ 512 requires 800 square feet of habitable floor area for one- and two-family dwellings.
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 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 rentalsShort-term rentals allowed with local rules. STR needs an annual, inspection-gated permit that expires each December 31, and no permit issues without proof of registration for the county occupancy tax. Occupancy is capped at two persons over the age of two per bedroom, and Code Enforcement may set it lower. Separate question from whether you can build the unit.
- Zoning codefranklindelco-ny.gov/download_file/view/ef9227fe-5324-43c3-841f-c6e13c2ccf48/248
Sizing up a specific parcel in Franklin?
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Building a full house instead?
A standard-finish house in Franklin runs $191–250/sq ft, about $345k–450k at 1,800 sq ft , plus roughly $1,947 for a conforming lot. See what it costs to build a house in Franklin.
ADU cost in nearby towns
All Delaware County towns: Andes · Delhi · Middletown · Sidney · Walton · Delhi (Village) · Hancock (Village) · Sidney (Village) · Walton (Village)
More on Franklin: Can you build an ADU here? · Zoning for new construction · Delaware County build cost
ADU cost in Franklin: common questions
How much does it cost to build an ADU in Franklin, NY?
An 800 sq ft accessory dwelling unit in Town of Franklin runs roughly $185k–245k at a standard finish, general-contractor margin included. A 400 sq ft studio runs about $125k–160k. 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 Franklin?
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 $233–305/sq ft against $191–250/sq ft for a full house, even though it is the same trades doing the same work.
Are ADUs allowed in Franklin?
Town of Franklin has 6 districts. 4 districts allow ADUs with occupancy restrictions, 2 require a special-use permit. Check the specific address with the free ADU checker or confirm with the building department before you spend money on design.
Can I rent an ADU in Franklin short term?
Short-term rentals allowed with local rules for Town of Franklin. 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 Delaware 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 Franklin vary by district and often carry exceptions this page does not show; zoning last reviewed 2026-08-24; verify with the municipality before relying on any answer. Sources: the Offsite / Aldo cost engine and zoning dataset.