If you own a single-family rental property in Baltimore — or you’re looking to expand your portfolio — one of the most significant changes in Maryland real estate law is about to take effect. Accessory dwelling units, long restricted or outright prohibited under Baltimore’s zoning code, are set to become legal citywide by October 1, 2026 under the Maryland Accessory Dwelling Units Act of 2025.

For Baltimore landlords and investors, this isn’t just a zoning footnote. It’s a real opportunity to add a second rentable unit to a property you already own — without buying anything new. But it also comes with new compliance requirements, construction permit obligations, and rental licensing rules that you need to understand before breaking ground or signing a contractor.

What Is an Accessory Dwelling Unit?

An accessory dwelling unit (ADU) is a secondary, self-contained residential unit located on the same lot as a primary single-family home. It has its own entrance, kitchen, bathroom, and sleeping space — making it a fully independent dwelling, not just a shared room or basement bedroom.

Under Maryland’s ADU Act of 2025, ADUs are defined as secondary dwelling units no larger than 75% of the primary unit’s footprint. They come in three forms: interior ADUs (a basement or attic converted into a self-contained unit), attached ADUs (an addition built onto the main structure with a separate entrance), and detached ADUs (a stand-alone structure on the same lot, such as a garage apartment or backyard cottage).

The most common ADU candidates in Baltimore’s dense rowhouse neighborhoods are basement conversions — lower-level spaces that already have separate entrances on many Fells Point, Hampden, Canton, and Federal Hill properties. In Baltimore County suburbs, detached garage conversions are frequently the most practical option.

What Maryland’s ADU Act of 2025 Actually Requires

Governor Wes Moore signed HB 1466 during the 2025 legislative session, making Maryland one of a growing number of states to mandate local ADU legalization. The law is clear: every jurisdiction with planning and zoning authority — including Baltimore City and Baltimore County — must pass a local ordinance permitting ADU development on any lot with a single-family detached dwelling by October 1, 2026.

The state law also prohibits local governments from imposing “unreasonable restrictions” that would effectively block ADU development — disallowing excessive parking requirements, setback rules, or fee structures that effectively price ADUs out of reach. ADUs must be excluded from density calculations, meaning they won’t count against zoning unit limits the way a traditional conversion might.

Baltimore City vs. Baltimore County: Where Things Stand

The two jurisdictions Sungate serves are in very different positions heading into the October 2026 deadline — and that matters if you’re deciding where to invest.

Baltimore City does not currently have a clear, citywide ADU ordinance. Most homeowners cannot legally add a backyard cottage or convert a basement into an independent rental unit without navigating a cumbersome special approval process. As of February 2026, the Scott administration had not yet submitted a bill to comply with the state mandate — a significant delay with just months to go. When Baltimore City does adopt its ordinance, it will almost certainly be shaped by pressure from both housing advocates (who want ADUs as an affordability tool) and neighborhood groups (who may push for restrictions). Landlords in Baltimore City should watch the city council calendar closely in Q3 2026.

Baltimore County already permits ADUs, but under restrictive conditions. The most important: ADUs in Baltimore County are currently only permitted on owner-occupied properties. If you own a rental property in Towson, Pikesville, or Catonsville that you don’t live in, you may not qualify under current County rules — though the state mandate may force loosening of those restrictions before October 2026.

The Compliance Checklist: What You Need to Rent an ADU Legally

Building an ADU is only the first step. To legally rent the unit as a residential dwelling in Baltimore, you’ll need to navigate several compliance layers — the same layers Sungate handles for every property in its portfolio of 400+ units.

Building permits are mandatory. Any ADU project requires building, electrical, and plumbing permits regardless of the unit type. Structural, electrical, and mechanical work requires licensed professionals and inspections at multiple stages. There are no shortcuts here — unpermitted construction creates legal liability, insurance voids, and rental license ineligibility.

A rental license is required before collecting rent. In Baltimore City, any residential rental unit must hold a valid rental license issued through DHCD. The license requires a property inspection; violations must be corrected within specific timeframes that determine whether you receive a 1-year, 2-year, or 3-year license cycle. An ADU is a new unit — it will need its own license prior to tenant move-in.

Lead paint compliance applies. If your property was built before 1978 (most Baltimore rowhouses were), the ADU must go through MDE lead paint inspection before each new tenancy, consistent with Maryland’s lead law. As of January 1, 2026, lead paint inspections must be renewed every two years — a requirement that applies to ADUs the same as any other unit.

Smoke and CO detector requirements apply to the new unit. Maryland requires 10-year sealed lithium battery smoke alarms on every level and outside every sleeping area. Carbon monoxide detectors are required outside every sleeping area if the unit has fuel-burning equipment. These must be installed, tested, and documented before a tenant moves in.

What ADUs Mean for Baltimore Investors: The Numbers

The financial case for ADUs in Baltimore is straightforward. If you already own a single-family rental in neighborhoods like Hampden, Federal Hill, or Waverly, you’re already covering property taxes, insurance, and maintenance on a lot that could be generating a second income stream.

A well-converted basement ADU in Baltimore typically requires $40,000–$80,000 in construction investment depending on the scope of work — egress windows, bathroom, kitchen, electrical panel separation, and soundproofing. At $1,100–$1,300/month in rent (a conservative figure for a one-bedroom ADU in a walkable Baltimore neighborhood), the unit pays back its construction cost in five to seven years. After that, it’s pure additional cash flow on a property you already own.

The property value impact is equally significant. Appraisers generally treat an ADU as adding 10–25% to overall property value, depending on location and rental income. For a Baltimore property currently valued at $218,000 — the current median — a legal, permitted ADU could push assessed value meaningfully higher while simultaneously generating monthly income.

The key word in all of this is legal. Unpermitted basement apartments already exist throughout Baltimore — and they expose owners to fines, forced vacant orders, and eviction proceedings with no recourse. The October 2026 mandate opens a path to do this properly, with the protection of a legal rental license and the ability to screen and place tenants with full legal standing.

What to Do Before the October 2026 Deadline

You don’t need to wait for Baltimore to pass its local ordinance to start planning. Here’s how to use the next four months wisely.

First, evaluate your property. Look at your lot size, basement dimensions, existing utilities, and whether there’s a separate entrance or the potential to create one. In Baltimore City rowhouses with rear alleys, detached garage conversion may also be possible. In Baltimore County, check whether you meet the owner-occupancy requirement under current rules.

Second, check zoning. Even before the state mandate takes effect locally, some Baltimore properties may already qualify for special exceptions or variances. A compliance review can tell you whether you’re in a position to move quickly once the ordinance passes.

Third, budget realistically. Construction costs, permit fees, rental license applications, lead inspections, and professional property management all factor into your first-year economics. Get a clear picture before you start.

Finally, think about management from day one. An ADU is a separate dwelling with its own tenant, its own lease, its own maintenance requests, and its own compliance calendar. If you’re already self-managing your primary rental unit and feeling stretched, adding an ADU without professional management support is a recipe for burnout — and compliance gaps.