Aberdeen MD ADU Rules 2026: Adopted September 28, Effective October 19

Aberdeen adopted Ordinances 26-O-06, 26-O-07 and 26-O-08 on September 28, 2026. All three final documents list October 19, 2026 as the effective date. The package is now effective. It removes the former 500-square-foot zoning minimum, revises size and residential setback rules, adds a parking-waiver process and exempts qualifying ADUs from specified water/sewer charges. Confirm city limits, zoning, unit classification and site conditions before paying for final plans.

1. Quick answer: can you build an ADU in Aberdeen today?

Effective October 19, Aberdeen’s ADU package removes the former 500-square-foot zoning minimum, limits an ADU to 75% of the primary dwelling’s size, and sets 6-foot side and rear setbacks in the residential dimensional table. The general parking rule is 1 off-street space, with a TOD exemption and an ADU waiver process. Owner-residency requirements, permits and other site standards still apply. Confirm whether the City will classify your proposal as an ADU or an accessory apartment.

If you are not certain that the property is actually inside Aberdeen City limits, use the Maryland ADU Jurisdiction Finder before relying on this guide.

2. Current ADU definitions and size rules

The revised §235-7 defines an ADU as a secondary dwelling on the same lot, parcel or tract as a primary owner-occupied single-family detached dwelling, subordinate in use and no larger than 75% of the primary dwelling. It includes a separate structure or an attached addition. Internal basement or upper-floor units and apartments in detached garages are directed to the separate dwelling, accessory apartment definition. See 26-O-06, pp. 2–4.

The signed ordinance makes these size changes:

• Minimum floor area: §235-22F exempts ADUs and accessory apartments from the zoning minimum dwelling floor-area requirements. The former 500 sq ft rows are deleted; building and safety requirements still apply.
• ADU maximum: the definition limits an ADU to 75% of the primary dwelling’s size.
• Accessory-apartment maximum: §235-22E changes the limit from 50% to 75% of the principal structure’s above-grade living area shown in Maryland SDAT records.
• TOD qualification: §235-22C states that the floor-area section does not apply in TOD districts. Confirm the applicable classification and measurement basis for a TOD parcel, basement or garage conversion.

3. Ordinance 26-O-06: the main Aberdeen ADU zoning rewrite

Ordinance 26-O-06, effective October 19, authorizes and regulates ADUs associated with a single-family detached primary dwelling. Its definition and permitted-location provisions refer to owner occupancy; the permit affidavit expressly allows residency in either dwelling. The main rules are summarized below.

The signed ordinance and relevant unchanged provisions establish:

• Permitted locations: Appendix A lists ADUs and accessory apartments as permitted uses in R-1, R-2, R-3, B-1, B-2, IBD and TOD, and not permitted in B-3 or M-1. The Residential Overlay provision also permits an ADU with an existing qualifying dwelling. A permitted-use label does not approve a particular lot. 26-O-06, p. 18 and §235-18.
• Residential side/rear setbacks: the new Table I lists 6 ft for exterior ADUs and accessory apartments. Internal basement or upper-floor units have no separate side/rear setback under these provisions; the principal structure must meet applicable lot requirements. §235-21C and Table I, p. 9; §235-23D(4), p. 12.
• Other placement rules: detached accessory structures must be at least 6 ft from other buildings on the lot. Required front yards, recorded easements, and street-facing yards on corner or through lots still constrain placement. Business and TOD accessory-structure rules can differ; confirm the district rules and treatment of an attached ADU addition. §235-27E–G, p. 14; published §§235-23F and 235-27J–L.
• Parking: §235-25C requires 1 off-street space per ADU or accessory apartment unless another provision applies. The unchanged §235-25E exempts TOD districts. 26-O-06, p. 13; published §235-25E.
• Parking waiver: under §235-25F(3), the Planning Commission may recommend waiving ADU parking when site conditions, topography or adjacency to a public street or alley make extra parking unnecessary. The City Council gives final approval. Confirm the route for a unit classified as an accessory apartment. 26-O-06, pp. 13–14.
• Owner-residency affidavit: before an ADU building permit is issued, the owner must affirm residency in either the principal dwelling or the ADU. Do not assume the owner must live only in the main house, or that both units may be independently rented without owner residency. §235-27H(8), p. 15.
• Construction timing: an ADU may be constructed concurrently with the principal home, but the principal home must receive its Certificate of Occupancy before the ADU is occupied. This does not authorize a standalone ADU without a principal use. §235-27A–C, p. 14.
• Other accessory structures: the ADU is excluded from the 50% aggregate floor-area cap for other accessory structures, but its own 75% size limit still matters. §235-27I(1), p. 15.

These standards do not establish separate-sale rights, short-term-rental permission, a permitted number of units beyond the applicable code, or approval of an existing unpermitted dwelling. Ask Planning to resolve the ADU/accessory-apartment classification, TOD exceptions and any conflict affecting your design.

4. Ordinance 26-O-07: ADUs and Aberdeen’s growth-management rules

Ordinance 26-O-07, effective October 19, adds ADUs to the exemptions in Chapter 302’s school-capacity standards.

The zoning amendment separately excludes ADUs and accessory apartments from the lot’s density calculation under §235-21C. The operative change in 26-O-07 adds ADUs to the school-capacity exemption in §302-4A(3). 26-O-06, p. 9; 26-O-07, p. 2.

These density and school-capacity exemptions do not remove building, utility-capacity, stormwater or other applicable site-review requirements.

5. Ordinance 26-O-08: fee exemptions effective October 19

Ordinance 26-O-08 exempts qualifying ADUs from specified connection charges while retaining conditions for the meter-charge exemption.

The changes to §A550-1A, effective October 19, are:

• Water area connection charge: ADUs are exempt under A(5)(f).
• Water meter charge: exemption is conditional under A(6)(f)–(g), as explained below.
• Sanitary sewer area connection charge: ADUs are exempt under A(7)(f).

These exemptions do not make utility work, all permit fees or ongoing service bills free. Trenching, service modifications, plumbing, engineering, meter configuration, restoration and other costs can remain. Confirm the City’s assessment, especially if the proposal is classified as an accessory apartment.

6. Why Aberdeen is acting now: Maryland’s October 1, 2026 deadline

Maryland Land Use §4-504 requires covered local legislative bodies to adopt a local law authorizing accessory dwelling units on or before October 1, 2026. The statewide definition in §4-501 describes a qualifying ADU as a secondary dwelling unit on the same lot as a primary single-family detached dwelling and no greater than 75% of the size of the primary dwelling.

The state framework also addresses issues such as growth-limit treatment, side/rear setback restrictions and additional ADU parking requirements. That is why Aberdeen’s September package spans zoning, growth management and fees rather than only adding one new definition to the code.

See our Maryland ADU October 1 Deadline Guide and Maryland County & City ADU Rules Tracker for the statewide transition.

7. Effective rules at a glance

8. Aberdeen ADU permit path: City permit, County inspections

Aberdeen has an important split in the permitting workflow.

Building permits are applied for through the City of Aberdeen. The City’s Department of Planning and Community Development reviews zoning and permit materials. After a permit is issued, the City says inspections for building, plumbing, electrical and mechanical work are conducted by the Harford County Department of Inspections, Licenses and Permits (DILP).

Aberdeen Public Works separately handles reviews/inspections related to grading, stormwater and public infrastructure, including water meters and water/sewer connection services.

9. What Aberdeen homeowners should do before finalizing plans

1. Confirm the property is actually inside Aberdeen. Use the Jurisdiction Finder.
2. Identify the zoning district. The current code uses district-specific standards, so a citywide setback assumption is unsafe.
3. Confirm service configuration, meter capacity and remaining charges. The two area-connection exemptions do not eliminate all utility costs.
4. Confirm the unit’s classification and design calculations. Bring the proposed floor area, SDAT record where relevant, site setbacks, parking plan and owner-residency affidavit requirements.
5. If an application was already pending before October 19, obtain the City’s written determination of the applicable rules.
6. Run the property through the Maryland ADU Property Feasibility Checker before spending heavily on design.

10. Adoption record and what to verify next

The public hearing was held September 14. The City has now posted the final ordinances, adopted September 28 and effective October 19, 2026.

The remaining project-specific questions are:

• How does the City classify the unit, and which district-specific exceptions apply?
• If an earlier application is pending, which provisions govern it?
• What floor-area measurement, site setbacks, parking approval and owner-residency documents are required?
• What service connection and meter-capacity assessment applies?
• Which permit, inspection and outside-agency approvals are required?

Keep the final ordinance and the City’s dated project-specific response with your plans.

11. Bottom line

Aberdeen’s three-ordinance ADU package is effective October 19, 2026. The former 500 sq ft zoning minimum is gone; the adopted rules establish the size limits, residential setbacks, parking-waiver route, residency affidavit and specified utility-charge exemptions described above. District exceptions and parcel-specific permits still matter.

For a homeowner planning now, the safest sequence is: confirm Aberdeen jurisdiction → identify zoning and unit classification → check size, site and residency requirements → resolve parking and utility assessments → obtain the required approvals before construction.

Next step: use the Maryland ADU Jurisdiction Finder, then run the Property Feasibility Checker and review the Maryland ADU Rules Tracker.

Primary sources used for this Aberdeen guide

• Final Ordinance 26-O-06 — zoning
• Final Ordinance 26-O-07 — school capacity
• Final Ordinance 26-O-08 — fees
• City of Aberdeen — Public Hearings (26-O-06, 26-O-07, 26-O-08)
• City of Aberdeen — 2026 Legislation Status
• City of Aberdeen Development Code — Definitions
• City of Aberdeen Development Code — Lot, Floor Area, Parking and Accessory Standards
• City of Aberdeen — Building Permit Procedure and Documents
• Maryland Land Use §4-501 — ADU Definition
• Maryland Land Use §4-504 — Local ADU Requirements

Maryland ADU Guide is maintained by Gijo John as an independent research publication. We prioritize enacted code, official legislative records and current government guidance. Proposed legislation is not treated as law. This page is for planning information and is not legal, architectural or permit advice.