Who it suits
This concept turns a basement or an unused wing into a one-bedroom apartment with its own entrance. Whether that use is allowed depends on your municipality and property. It’s a concept, not a completed build or an approved plan.
How it lives
A private outside entry leads into the kitchen and living space, with the bedroom and bath tucked away. The bedroom needs an egress window large enough to climb out of in a fire, and the apartment needs its own smoke and carbon-monoxide alarms and a fire-rated separation from the main house.
What changes the cost
Basements decide the budget early. Low ceilings, water problems, drains that sit below the sewer line, and the need for egress windows can each add real cost, and a wing conversion depends on what’s inside the walls. A site visit helps identify what needs further checking before design. Compare the work involved in different ADU forms and ask for an itemized estimate.
What to check with your town
Check whether an internal apartment is allowed, how its size is measured, the bedroom limit and any owner-occupancy requirement. Start with the town-fit table on this page and confirm the requirements with your code office.
What moves the price
- Ceiling height and egress windows
- Water and moisture problems
- Drain lines below the sewer level, which may need a pump
- Heating, cooling and fresh air for a below-grade space
What to check in each municipality
A first comparison with the codes we’ve read. A listed restriction identifies a conflict with this concept. Other results require local confirmation; missing research does not mean a ban or approval. Your zoning district, your lot and the municipality’s review still decide.
| Municipality | Screen | Size rule | Checked |
|---|---|---|---|
| Town of Clarkson | Below the 600 sq ft one-bedroom minimum | No more than 30% of the main home's living space (unit minimums 450 sq ft efficiency, 600 sq ft one-bedroom) | October 4, 2026 |
| Village of Fairport | Requires local confirmation of the district, size rule and approvals | 650 sq ft | October 4, 2026 |
| Town of Penfield | Family members only, so it can’t be rented. Size limit: No more than 30% of the total area of the residence. The main house’s size alone is not enough to calculate this limit | No more than 30% of the total area of the residence | October 4, 2026 |
| Village of Pittsford | Only within this code’s size limits; check them | No square-foot cap; house-size and structure-size tests apply | October 4, 2026 |
| Town of Canandaigua | Requires local confirmation of the district, size rule and approvals | No separate cap; the district's bulk and area rules for a single-family home apply | October 3, 2026 |
| Town of East Bloomfield | Family members only, so it can’t be rented. Only within this code’s size limits; check them | Detached: 500 to 850 sq ft gross floor area. In-law apartment: no size cap found | October 3, 2026 |
| Town of Perinton | No ADU-specific route found; ask the municipality for a written determination | Not applicable | September 16, 2026 |
| City of Rochester | Rule change under study; confirm the current route with the municipality | Conversion: building at least 1,500 sq ft and lot at least 6,000 sq ft, plus unit minimums | October 4, 2026 |