Last researched: September 19, 2026. Port Deposit is one of the Maryland municipalities that already has a detailed accessory dwelling unit section in its zoning ordinance. Section 176 allows ADUs in the ST, RM and CCD districts subject to local conditions, including owner occupancy, a one-ADU-per-lot rule, parking and a Town Zoning Certificate. The same section, however, limits an ADU inside the principal dwelling to no more than 30% of the gross floor area of that dwelling. Maryland Planning’s current HB 1466 guidance says jurisdictions may not cap ADUs below the state’s 75% limit, so the older Port Deposit size standard should not be treated as the final 2026 answer without confirmation from the Town.
Homeowner takeaway: Port Deposit has real ADU rules, but it also has a 2026 state-law transition, a Chesapeake Bay Critical Area overlay and unusually important historic-review issues. Before buying plans, ask Town Hall which enacted ADU ordinance currently controls your parcel and whether Historic Area Commission, floodplain or Critical Area review applies.
Port Deposit ADU planning snapshot
| Question | What we verified |
|---|---|
| Current Town ADU section | Section 176 of the zoning ordinance expressly regulates accessory dwelling units. |
| Residential districts named in § 176 | ST — Suburban Transition Residential; RM — High Density Residential; and CCD — Community Core. |
| Owner occupancy | The legacy rule requires the owner to occupy at least one dwelling unit on the premises. |
| Number of ADUs | The residential portion of § 176 allows one ADU per lot. |
| Legacy internal-ADU size rule | At least 600 sq ft and no more than 30% of the gross floor area of the principal dwelling. |
| Legacy accessory-building rule | At least 600 sq ft, no more than two bedrooms, and the ADU must occupy less than 50% of the accessory structure. |
| Parking | The current section requires off-street parking under Article XVI. Maryland’s 2026 law places additional conditions on ADU parking requirements. |
| Town permit | Section 176 requires a Zoning Certificate approved by the Zoning Inspector. |
| Historic review | The Town says exterior projects may require a Historic Area Commission Certificate of Appropriateness; HAC does not review interior projects. |
| Critical Area | Port Deposit’s RCA regulations contain a separate ADU standard, including same-sewage-system and 100-foot/900-sq-ft language. |
| County permit | The current Town application includes a determination for whether a Cecil County permit is also required. |
| Final 2026 ADU amendment | I did not find a separate 2026 ADU ordinance in the Town ordinance library or public notices reviewed on September 19, 2026. Confirm the current controlling ordinance with Town Hall. |
Port Deposit already has a specific ADU section
Port Deposit’s current zoning ordinance took effect April 23, 2024. Unlike municipalities where homeowners must infer ADU treatment from generic accessory-use rules, Port Deposit has a section titled “Accessory Dwelling Units.”
Section 176 says residential ADUs may be permitted in three zoning districts:
- ST — Suburban Transition Residential District, intended for medium-density residential growth;
- RM — High Density Residential District, which allows a mix of housing types; and
- CCD — Community Core District, the historic downtown-oriented mixed-use core.
That district language matters. A Port Deposit address alone does not prove that the lot is eligible. Confirm the parcel’s actual zoning district before designing an ADU.
The legacy Port Deposit rule requires owner occupancy and one ADU per lot
Under the residential portion of Section 176, the owner of the residential property must occupy at least one of the dwelling units on the premises. The section also limits the property to one accessory dwelling unit.
Those are current posted zoning conditions, but Port Deposit is approaching Maryland’s October 1, 2026 deadline for local HB 1466 implementation. Ask the Town whether those provisions have been retained, modified or superseded in any newer ordinance or administrative guidance.
The 30% size cap is Port Deposit’s biggest 2026 conflict
For an ADU located inside the principal dwelling, Section 176 currently requires at least 600 square feet and says the unit may not exceed 30% of the gross floor area of the dwelling in which it is located.
Maryland’s statewide definition now allows an ADU up to 75% of the size of the primary single-family detached dwelling. The Maryland Department of Planning goes further in its HB 1466 implementation FAQ: because covered jurisdictions must authorize ADUs consistent with the state definition, they may not impose a local maximum below the 75% limit.
For example, 30% of a 2,000-square-foot primary dwelling is 600 square feet, while 75% is 1,500 square feet. That does not mean every homeowner should build a 1,500-square-foot ADU. It means the 30% local ceiling should not be relied on as the final 2026 legal maximum without checking the Town’s updated implementation.
Before choosing a plan, use our Maryland ADU size guide and then ask Port Deposit how it currently measures the primary dwelling for the state 75% calculation.
Accessory-building ADUs have a different legacy rule
Section 176 also addresses ADUs located in accessory buildings. Under the current posted wording, the unit must be at least 600 square feet, may contain no more than two bedrooms and must occupy less than 50% of the accessory structure.
That is especially relevant to a garage or outbuilding conversion. A homeowner should not assume that converting an existing accessory building is automatically allowed simply because the building already exists. Confirm the current ADU size standard, the accessory-structure setbacks, parking, building-code requirements and whether the structure sits in the Historic or Critical Area overlay.
Interior ADUs also have an exterior-appearance rule
If the ADU is located inside the principal dwelling, Section 176 says the entrance and design should, to the degree reasonably feasible, preserve the appearance of a single-family residential structure. It also says a new external entrance facing a road or street may not be added.
In Port Deposit, that requirement can overlap with historic-preservation review. An interior conversion may avoid Historic Area Commission review if there are no exterior changes, while a new exterior entrance, dormer, addition or detached structure can trigger a separate design-review question.
Historic review is a major Port Deposit-specific issue
Port Deposit’s current Zoning Certificate application explains that the Town is on the National Historic Register and that the majority of structures contribute to the historic district. Before exterior repair, restoration, alteration or demolition work begins, the applicant must obtain the required Town zoning approval, and an exterior project may also require a Historic Area Commission Certificate of Appropriateness.
The Town specifically states that the Historic Area Commission does not review interior projects. For an ADU, this creates a useful distinction:
- an internal conversion with no exterior work may have a simpler historic-review path;
- an attached addition can require exterior design review; and
- a new detached ADU in the historic area can require review of its scale, materials, siting and relationship to surrounding historic structures.
Do not order a prefab exterior design before confirming this. A unit can satisfy dimensional zoning rules and still need historic-design approval.
Port Deposit’s Critical Area code contains a second ADU rule
Because Port Deposit sits along the Susquehanna River, the Chesapeake Bay Critical Area is another important layer. In the Resource Conservation Area (RCA), the zoning ordinance contains a supplemental ADU provision that applies when the ADU use is permitted by the underlying zoning district.
The RCA provision allows one additional dwelling unit as part of the primary dwelling if it uses the same sewage-disposal system and either:
- is inside the primary dwelling, or has its entire perimeter within 100 feet of the primary dwelling and does not exceed 900 square feet of total enclosed area; or
- is inside the primary dwelling and does not increase the lot coverage already attributed to the primary dwelling.
The section also says the additional unit cannot be subdivided or conveyed separately from the primary dwelling.
The RCA 900 sq ft figure is not a universal Port Deposit ADU maximum
The 900-square-foot language belongs to the Town’s Critical Area overlay. It should not be read as the ordinary townwide maximum for every ADU. A property can be subject to the underlying zoning district, the general ADU section and Critical Area environmental rules at the same time.
If your parcel is near the river, wetlands or tidal areas, ask Town Hall to confirm its Critical Area classification before design. The current Town application specifically includes review for zoning, floodplain and Critical Area regulations.
Port Deposit currently requires off-street parking, but Maryland law changes the analysis
Section 176 says off-street parking must be provided under Article XVI of the Town zoning ordinance. Maryland Land Use § 4-504 now says a jurisdiction that imposes additional off-street parking requirements on ADUs must first complete the required parking study and must provide a waiver process.
I did not locate a Port Deposit ADU parking study or a separate 2026 ADU parking ordinance in the official materials reviewed on September 19, 2026. That does not prove one has not been completed. Ask the Town which parking requirement and waiver procedure apply to a current application.
The Town Zoning Certificate is the first permit step
Section 176 requires the property owner to file for a Zoning Certificate, and the Zoning Inspector must approve the certificate for the ADU. Port Deposit’s current application requires plans and supporting information and states that the Town will review compliance with zoning, floodplain and Critical Area regulations.
The same application also includes a field for whether a Cecil County permit is required. Port Deposit’s building-code provisions place County personnel in the construction-permit and inspection process for qualifying work. For an ADU involving structural, plumbing, electrical or other building work, confirm the Town-to-County sequence before construction begins.
A practical Port Deposit ADU workflow
- Confirm the property is inside Port Deposit municipal limits.
- Identify whether the zoning is ST, RM, CCD or another district.
- Ask Town Hall which current ADU ordinance controls the application.
- Confirm whether the 30% internal-ADU cap has been superseded for HB 1466 compliance.
- Check Historic Area status and whether a Certificate of Appropriateness is required.
- Check floodplain and Chesapeake Bay Critical Area status.
- For an RCA parcel, confirm the applicable Chapter 134 ADU standards.
- Verify size, accessory-structure setbacks, height, lot coverage and parking.
- Prepare the Town-required building/site/design plan and photographs.
- Apply for the Port Deposit Zoning Certificate.
- Complete Historic Area Commission review if required.
- Obtain any Cecil County building and trade permits identified by the Town.
- Complete inspections before occupying the unit.
What to ask Port Deposit before paying for plans
- What enacted ordinance currently governs ADUs?
- Has Section 176 been amended for Maryland HB 1466?
- Does the 30% maximum still apply to an internal ADU?
- Does the 600-square-foot minimum still apply?
- How is the primary dwelling measured for Maryland’s 75% definition?
- Is owner occupancy still required?
- Which districts currently permit attached and detached ADUs?
- What accessory-structure setbacks apply?
- What parking rule and waiver process apply?
- Has the Town completed an ADU parking study?
- Is the parcel in the Historic Overlay District?
- Will the proposed exterior work require a Certificate of Appropriateness?
- Is the parcel in the Critical Area or floodplain?
- Which Cecil County permits will be required after Town approval?
Port Deposit MD ADU FAQs
Does Port Deposit allow ADUs?
Yes. Port Deposit’s current posted zoning ordinance has a dedicated ADU section and says ADUs may be permitted in the ST, RM and CCD districts, subject to the section’s conditions. Confirm the current 2026 ordinance before relying on older size and parking limits.
What is the old Port Deposit ADU size limit?
For an ADU inside the principal dwelling, the current posted Section 176 requires at least 600 square feet and no more than 30% of the principal dwelling’s gross floor area. Maryland Planning says local jurisdictions may not cap ADUs below the state’s 75% limit, so the 30% maximum should be verified against Port Deposit’s current 2026 implementation.
Can I convert a detached garage into an ADU in Port Deposit?
Section 176 contains rules for ADUs in accessory buildings, including a 600-square-foot minimum, a two-bedroom limit and a requirement that the unit occupy less than 50% of the structure. A current project still needs parcel-specific confirmation of zoning, state-law compliance, building code, setbacks, parking, historic review and Critical Area restrictions.
Will a Port Deposit ADU need historic approval?
Possibly. The Town says exterior projects may require a Historic Area Commission Certificate of Appropriateness. HAC does not review interior projects. Confirm whether your parcel and proposed exterior work are subject to review before finalizing the design.
What if my property is in the Critical Area?
Port Deposit’s Resource Conservation Area provisions contain additional ADU standards involving sewage disposal, proximity to the primary dwelling, enclosed area and lot coverage. Those rules can apply in addition to the general zoning requirements.
Who should I contact about a Port Deposit ADU?
Start with Port Deposit Town Hall at 64 South Main Street, Port Deposit, Maryland 21904. The Town lists 410-378-2121 for zoning and permit questions.
Primary sources checked
- Town of Port Deposit — Ordinances
- Town of Port Deposit — Planning & Zoning Commission
- Town of Port Deposit — Applications, Forms & Permits
- Town of Port Deposit — Historic Area Commission
- Town of Port Deposit — Public Notices
- Maryland Department of Planning — HB 1466 ADU FAQ
- Maryland Land Use § 4-501 — ADU definition
- Maryland Land Use § 4-504 — Local ADU law requirements
Maryland ADU Guide is an independent research publication, not the Town of Port Deposit, Cecil County, the Historic Area Commission, the Critical Area Commission, a law firm, architect or contractor. Port Deposit’s rules can change during Maryland’s 2026 ADU implementation period. Confirm the current ordinance and parcel-specific requirements before spending money on design or construction.
What to do next
Start by confirming municipal jurisdiction, zoning and whether historic, floodplain or Critical Area review applies.
- Find Who Reviews My Property.
- Gather your parcel identifier, survey, zoning district and utility information.
- Ask Port Deposit which current ADU ordinance and overlay rules apply.
- Continue to your planning workspace.
Planning guidance is not permit approval.