Clarkson's 2025 code allows a one-bedroom ADU, detached in AR and RS-20, up to 30% of the house size, with the owner on site, by special permit.
The code allows an ADU only with a special use permit, which a board must approve, usually after a public hearing. Approval is not automatic.
Whether any of this applies to your lot depends on your zoning district and your property.
The rules we found
| What the code says | Allowed with a special use permit |
|---|---|
| Detached (backyard) unit | Yes, in AR and RS-20, behind the main building |
| Inside or attached | Yes; RS-10 allows internal units only |
| Size limit | No more than 30% of the main home's living space (unit minimums 450 sq ft efficiency, 600 sq ft one-bedroom) |
| Bedrooms | 1 |
| Owner must live on site | Yes |
| How approval works | Planning Board special use permit after a public hearing, plus site plan review (§§140-23.3B, 140-41.3) |
| Other rules | One ADU per home. Not allowed on a lot or in a building that doesn't meet today's zoning rules (called 'nonconforming'). You need room for one more car in your existing driveway. A detached ADU goes behind the house, at least 15 ft from the side and back lot lines in the AR district (10 ft in RS-20). An ADU inside the house needs its entrance on the side or back wall, and the code officer may inspect once a year. |
Code section: §§140-23.4, 140-23.5, 140-23.17 (Clarkson additional use regulations). Chapter 140 replaced October 28, 2025 by Local Law 5-2025.
What the size rule means for your house
With a 1,600 sq ft house, the largest ADU this rule allows is about 480 sq ft.
The smallest ADU allowed here is 450 sq ft, so the house needs about 1,500 sq ft or more for any ADU.
A one-bedroom must be at least 600 sq ft, which takes a house of about 2,000 sq ft.
sq ft
Rounded down to the nearest 10 sq ft. Towns measure differently (some count only finished living space, some leave out the garage), so ask the code office how it measures yours.
What this means for your plans
- Expect a public hearing where neighbors can speak, and a board decision that can take a few months. How special use permits work.
- The owner has to live on the property. If you plan to move away, spend winters somewhere else or sell, read the owner rule above closely. Renting and owner rules.
Before you spend money on drawings
- Confirm the Town of Clarkson governs your lot: it should be the municipality on your property tax bill.
- Find your zoning district on the municipal zoning map; the rules above can differ by district.
- Call or write the code office with your address and what you’re picturing, and ask for the answer and the code section in writing.
- On septic or a well? Ask the Monroe County health department whether the system can serve an extra bedroom. On public sewer? Ask your sewer district.
Our guides explain the approval process, site and utility checks and what an ADU costs.
Sources
General information, not legal advice. The Town of Clarkson decides what can be built on your property.