Caroline County ADU Rules 2026: 50% Size Cap, Owner Occupancy, 30-Day Notice & HB 1466 Conflict

Caroline County already allows accessory dwelling units, but its current published rules are not yet fully aligned with Maryland’s 2025 ADU law. The County permits one ADU inside a principal dwelling or in a detached accessory structure, subject to owner occupancy, shared water/sewer facilities, location limits and a 30-day neighbor-notice process. The biggest 2026 issue is size: Caroline still caps an ADU at 50% of the principal dwelling and 1,000 square feet, while Maryland says qualifying local ADU laws may not limit units below 75% of the primary dwelling’s size.

The safest way to plan in Caroline County is to distinguish the currently published County process from the state-law changes local governments must implement by October 1, 2026. Caroline County’s own public-outreach materials acknowledge HB 1466 and that local ADU laws must be adopted or revised for consistency by that deadline. Until a replacement ordinance is enacted and published, homeowners should not assume the existing 50%/1,000-square-foot limits are the final 2026 framework.

Last verified: September 13, 2026. This page reports the County’s currently published zoning code and application materials alongside Maryland’s HB 1466 implementation guidance. Maryland ADU Guide is an independent research publication and is not legal, zoning, architectural, engineering or permitting advice.

Caroline County ADU status at a glance

What Caroline County’s current ADU rules say

Section 175-83 allows one accessory dwelling unit per lot. The County defines an ADU as separate living quarters within the principal dwelling or in a detached accessory structure, with its own kitchen, living and sleeping areas.

The County’s current application and checklist recognize three practical pathways: an attached/interior ADU, a detached ADU, or conversion of an existing building. An existing building used for conversion must generally be at least five years old. Mobile homes are not permitted as ADUs under § 175-83.

The 50% size rule is the main 2026 conflict

Caroline County’s current code says an ADU must contain at least 400 square feet of habitable area, may not exceed 1,000 square feet of habitable area, and the total ADU area may not exceed 50% of the total area of the principal dwelling.

Maryland Department of Planning’s HB 1466 FAQ says local jurisdictions required to authorize ADUs consistent with the state definition may not limit ADU size below 75% of the primary single-family detached dwelling. The state also notes that HB 1466 does not prescribe one mandatory measurement method and recommends finished living area above grade for the primary dwelling.

How Caroline County’s 30-day neighbor-notice process works

Caroline’s current process is unusual compared with several Maryland counties. The County sends certified-mail notice to property owners whose property line is within 500 feet of the applicant’s property line. Those owners have 30 days to object in writing.

If no objection is received, the applicant must obtain the zoning certificate and/or building permit within one year after the objection period. If an objection is received, the applicant may apply to the Board of Zoning Appeals for a special use exception within six months. Maryland’s HB 1466 FAQ does not require ADUs to be approved by right, so a conditional or special-exception process can still be used if the local law otherwise complies with the state framework.

Owner occupancy, common ownership and utilities

The current County code requires either the principal dwelling or the accessory dwelling to be the residence of the property owner. It also requires the principal and accessory dwellings to remain in common ownership and prohibits subdividing them from one another.

The County’s application additionally states that the ADU may not have separate water and sewerage facilities from the principal dwelling. The Planning & Codes checklist requires Health Department approval, making water and wastewater capacity a real feasibility gate rather than a paperwork detail.

Where can a detached ADU be located?

The current Caroline County rule places an ADU in the side or rear yard, no closer to the front lot line than the principal dwelling. A detached ADU must generally be within 100 feet of the principal dwelling, within the building envelope and in compliance with applicable setback requirements.

Maryland’s HB 1466 framework separately says a local ADU law may not establish side or rear setbacks that exceed the setbacks otherwise applicable to accessory structures. Caroline County’s code allows some accessory structures under 750 square feet to sit as close as five feet from side or rear lot lines, so homeowners should ask Planning & Codes how the 2026 ADU framework is being reconciled with the accessory-structure setback rule on their parcel.

What does Caroline County require for ADU parking?

Section 175-83 currently says adequate parking must be provided for the ADU and all other uses of the property. The reviewed ADU section does not specify a fixed number of additional spaces.

Maryland HB 1466 becomes important if the County interprets this provision as requiring additional off-street ADU parking. The state says local governments that impose extra ADU parking requirements must first complete a parking study and must provide a parking-waiver process. Ask Planning & Codes whether any project-specific parking condition is being imposed under the current or forthcoming 2026 framework.

Building permits, septic, well and Critical Area review

Caroline County requires a building permit for new construction, additions, alterations, changes of occupancy and conversions. The County’s ADU materials call for a site plan, architectural floor plans/elevations and Health Department approval.

For properties using private well or septic systems, involve Environmental Health before final design. Caroline County’s land-development guidance specifically uses water/sewer verification and perc testing to resolve development capacity and site-design issues. Waterfront properties can also require Critical Area review even for some work that would not otherwise need a building permit.

Use our Maryland ADU Septic & Well Readiness Guide before paying for final plans if the property is not served by public utilities.

Do Caroline County rules apply inside incorporated towns?

Do not assume they do. Caroline County has ten incorporated municipalities: Denton, Federalsburg, Goldsboro, Greensboro, Henderson, Hillsboro, Marydel, Preston, Ridgely and Templeville. The County has expressly stated in another land-use context that municipalities control zoning and land-use decisions within their corporate limits.

If the property is inside a town, verify the town’s zoning authority before relying on § 175-83. Use the Maryland ADU Jurisdiction Finder when the controlling jurisdiction is unclear.

What Caroline County homeowners should do now

1. Confirm jurisdiction. County rules may not control inside an incorporated municipality.
2. Ask whether a 2026 HB 1466 replacement ordinance has been adopted or is being applied. Do this before relying on the 50%/1,000-sq-ft limits.
3. Confirm the size measurement method. Caroline’s current application uses total principal-dwelling area, while Maryland recommends finished living area above grade.
4. Map the side/rear buildable area. A detached ADU must satisfy the County’s location, building-envelope and distance rules unless a newer standard supersedes them.
5. Check water and wastewater capacity early. Health Department approval is part of the current ADU process.
6. Plan for the 30-day notice period. A neighbor objection can shift the application to the Board of Zoning Appeals.
7. Clarify parking in writing. Ask whether any additional space is required and, if so, what HB 1466-compliant waiver process applies.
8. Re-check immediately before spending. Caroline County has acknowledged the October 1, 2026 state deadline, so the local framework may change.

Primary sources used for this Caroline County guide

• Caroline County Code § 175-83 — Accessory dwelling units
• Caroline County — Accessory Dwelling Application
• Caroline County — Accessory Dwelling Requirements Checklist
• Caroline County — Building Permits / Zoning Certificates
• Maryland Department of Planning — HB 1466 ADU FAQ
• Caroline County — Public Outreach materials referencing HB 1466 and October 1, 2026 local deadline

For statewide comparison, use the Maryland County ADU Rules Tracker. Maryland ADU Guide is maintained by Gijo John as an independent research publication.