ADU housing laws and regulations in Baltimore — 2026

Maryland's Accessory Dwelling Units Act of 2025 (HB 1466, cross-filed as SB 891) took effect October 1, 2025 and gave every county and municipality until October 1, 2026 to allow an ADU on any lot zoned for a single-family detached house.

Baltimore one-bedroom rents rose 8% year over year in Zumper's September 2026 data, so a legal second unit can create rental income on a lot you already own. Whether you can build that unit depends on which side of a county line your lot sits: the ADU Baltimore rulebook splits three ways, and as of September 28, 2026 Baltimore City had not enacted the ordinance the state deadline requires.

ADU rules in Baltimore at a glance

An ADU is a second, self-contained home on the same lot as a primary house, with its own kitchen, bathroom, and entrance. It can be a finished basement, a rear addition, a converted garage, or a backyard cottage. Where each jurisdiction stood on September 28, 2026:

• Baltimore City has no "accessory dwelling unit" use anywhere in Article 32, its Zoning Code. The only second-unit path today is converting a carriage house that existed on June 5, 2017, or winning a property-specific City Council ordinance.
• Baltimore County allows "accessory apartments" in any zone that permits single-family detached homes, but only on owner-occupied lots and only for occupants related to the household by blood, marriage, or adoption.
• Anne Arundel County allows ADUs as a conditional use in the RA, RLD, R1, R2, R5, R10, and R15 districts, with no minimum lot size and no added parking.
• Size caps run from none stated (City) to one-third of the house or 2,000 sq ft for interior units and 800 sq ft for detached units under an acre (County) to 800 sq ft or half the main house for detached units (Anne Arundel).
• Accessory structures top out at 15 feet in both the City and County. The County requires 2.5 feet from side and rear lines and limits accessory buildings to 40% of the rear yard; the City limits them to 50% of the required rear yard.
• Parking is close to a non-issue: the City eliminated off-street minimums citywide in 2025, Anne Arundel repealed its one-space ADU requirement in 2023, and no County ADU parking minimum appears in the retrieved code.
• Once a compliant local ordinance exists, state law caps an ADU at 75% of the primary home's size, bars impact fees on units under 750 sq ft, and limits any parking requirement to one space.

Are ADUs legal in Baltimore City and Baltimore County?

In Baltimore County, yes, with conditions that rule out most investor use. In Baltimore City, not yet, unless your lot has a pre-2017 carriage house or you can get the City Council to pass an ordinance for your address.

Baltimore City

"Accessory Dwelling Unit" does not appear in any Article 32 use table, and under § 1-205 a blank entry means the use is not permitted. That covers the detached and semi-detached districts R-1A through R-4 in Table 8-301 and the rowhouse and multi-family districts R-5 through R-10 in Table 9-301. § 8-201 goes further for R-1A through R-4 and limits each lot to one single-family dwelling while prohibiting conversion to multi-family.

Two narrow exceptions exist. § 15-504 lets you convert a carriage house that existed on June 5, 2017 into a dwelling in any Residential or OR district, provided it has at least 350 sq ft of gross floor area; after conversion you may not enlarge it by more than 20% in height or footprint. The other route is a property-specific council ordinance, the "CO" conditional use. Recent examples include Ordinance 25-038, signed September 15, 2025, which allowed 2001 West Baltimore Street to convert to three units in an R-8 district. Each of those took its own bill through the council, which is exactly the process HB 1466 was written to replace.

Baltimore County

Baltimore County permits an accessory apartment inside a single-family detached house, in an addition to one, or in a detached accessory building, in any zone that permits single-family dwellings, under BCZR § 400.4. Interior and addition units go through an administrative use permit at Permits, Approvals and Inspections (PAI). Detached units need a special hearing before the Office of Administrative Hearings (OAH), which was still granting them as recently as July 8, 2026.

The conditions are the problem for landlords. The owner must live in either the main house or the apartment, and Bill 7-23 kept the rule that occupants of both units "shall be family, related by blood, marriage or adoption." The permit also terminates when the property sells or the named occupants change.

Lot type matters under state law

HB 1466 reaches only lots where a single-family detached house is the primary dwelling. Rowhouse and townhouse lots get nothing from the state mandate, so a Canton or Hampden rowhouse owner still depends on whatever Baltimore City chooses to pass on its own. Anne Arundel County, for comparison, has allowed ADUs as a conditional use since Bill 6-23 took effect May 27, 2023.

Baltimore City vs Baltimore County ADU rules

The three jurisdictions differ on nearly every dimensional standard, and the code sections below are the ones a plan reviewer will cite back to you:

• Standard | Baltimore City | Baltimore County | Anne Arundel County
• Allowed types | Carriage-house conversion only (§ 15-504); no ADU use in Tables 8-301 or 9-301 | Interior or addition (§ 400.4.A); detached accessory building (§ 400.4.B) | Within or connected by breezeway, in a garage, or detached (§ 18-10-124(3))
• Max size | None stated; carriage house needs 350 sq ft and may grow no more than 20% (§ 15-504) | Interior: lesser of one-third of floor area or 2,000 sq ft (§ 400.4.A); detached: 800 sq ft under 1 acre, 1,200 sq ft at 1 acre or more (§ 400.4.B) | Detached: lesser of 800 sq ft or 50% of principal dwelling; internal must be smaller than principal (ADU Facts)
• Height | 15 ft for accessory structures (§ 15-501) | 15 ft; variance required above (PAI Zoning) | Not separately stated in § 18-10-124
• Setbacks | District yard requirements apply (§ 15-501); no ADU-specific number | 2.5 ft from rear and side lines (PAI Zoning) | District accessory-structure setbacks; no variance to reduce toward adjacent residential lots except for pre-May 27, 2023 structures (§ 18-10-124(9))
• Lot coverage | Accessory structures capped at 50% of required rear yard (§ 15-501) | Accessory buildings capped at 40% of rear yard (§ 400.1) | Not stated in retrieved sources
• Parking | No minimums citywide (Ord. 25-064) | No ADU-specific minimum in retrieved code | None required (Bill 6-23)
• Owner-occupancy | Not found in Article 32 | Required, plus family-only occupancy (§ 400.4; Bill 7-23) | Required only when the property is used as a short-term rental (§ 18-10-124(7))

Once each jurisdiction adopts a compliant ordinance, several state limits override anything stricter: setbacks may not exceed the existing accessory-structure setbacks, lot-size minimums may not exceed the minimum for the principal dwelling, and parking may not exceed one space (none within 0.75 miles of transit). Size works differently. The 75% figure is part of the state's definition of an ADU, not a floor a locality has to allow, and § 4–505 expressly lets local law set objective square-footage requirements. A county may keep a cap below 75%, which is why Anne Arundel's 800 sq ft / 50% detached limit is not itself a conflict with the state act.

What Maryland's HB 1466 and SB 891 change, and when

The 2025 preemption law is HB 1466 (Chapter 197) and its cross-file SB 891 (Chapter 196); Governor Moore signed both on April 22, 2025. SB 382 is the 2023 bill that created the ADU Policy Task Force whose work produced the 2025 act, and 2025 SB 382 concerns powered wheelchair repair, so if a contractor cites "SB 382" as the new ADU law, they have the wrong bill.

What local governments must do

Under the enacted text, each local legislative body must authorize ADUs on land zoned for single-family residential use, exclude ADUs from density calculations and growth limits, and decide complete applications within 90 days. The state defines an ADU as a secondary unit on the same lot as a single-family detached house, no larger than 75% of the primary dwelling, and subordinate in use and appearance.

The Maryland planning FAQ and Chapter 197 text also bar several local conditions:

• No added parking within 0.75 miles of mass transit, and no more than one off-street space elsewhere without a parking study
• No side or rear setbacks stricter than the existing accessory-structure setbacks
• No minimum lot size larger than the minimum for the principal dwelling
• No development impact fee or building excise tax on ADUs under 750 sq ft
• No ban on converting an accessory structure whose only car access is from an alley
• No deed, covenant, or HOA rule that unreasonably limits ADU development or long-term rental (short-term rental restrictions are expressly excluded)

Maryland recommends by-right approval but does not require it, so don't import assumptions from California’s code; a county may still run ADUs through a conditional-use or special-exception hearing. The historic-property carve-out is narrower than it first looks: subsection (C) of the covenant provision says "this section" does not reach a restriction on use on property listed in, or found eligible for, the Maryland Register of Historic Properties. That removes the covenant protection for those properties; it does not exempt them from the zoning mandate itself. Local short-term rental rules survive, and utilities keep authority over adequate capacity. The Maryland Association of Counties described the final bill as one where "amendments adopted during the legislative process preserved greater local flexibility" than the introduced version.

Timeline and where each jurisdiction stands

The dates that matter for a Baltimore-area owner:

1. April 22, 2025: HB 1466 and SB 891 signed.
2. October 1, 2025: Act takes effect. The utility, impact-fee, and covenant provisions apply from this date.
3. February 25, 2026: Maryland Department of Planning publishes its current model ordinance and assessment tool.
4. October 1, 2026: Deadline for every local legislative body to adopt a conforming ordinance.

Baltimore City missed the runway. The City Council received Council Bill 25-0066, the "Housing Options and Opportunity Act," on May 12, 2025, and it stalled at a December 1, 2025 hearing. Its Legistar record showed it still in committee on February 12, 2026.

Baltimore Brew reported on February 23, 2026 that the draft ADU language lacked definitions, named no districts, and left height, setbacks, and parking unaddressed. Critics said it "defies the state mandate."

Ryan Dorsey sponsored Council Bill 26-0195 in May 2026. It would let any single-family owner convert to two units or add a unit, including by building a detached unit by right on a rowhouse lot. Baltimore Brew reported a September 24 vote, and no enactment record existed on September 28.

Baltimore County had no 2024–2026 council bill titled as an HB 1466 response in its legislation index, and OAH kept processing applications under the existing family-only framework through July 2026. Whether that family requirement survives October 1, 2026 is unresolved; the state law neither imposes nor prohibits owner- or family-occupancy rules. Anne Arundel County already complies in outline and has a pending Bill 61-26 (introduced July 20, 2026) to revise its size definition.

In the meantime, you can apply for a County use permit or special hearing. You can also seek an Anne Arundel conditional-use approval or a City carriage-house conversion. For anything else in the City, check the Legistar record for Bill 26-0195 before you pay for drawings.

Which ADU types are allowed: basement, attached, garage conversion, detached

Four physical forms cover nearly every ADU project, and each jurisdiction treats them differently:

• A basement ADU is a finished, separately accessed unit in the lower level of the main house, with code-compliant bedroom egress, a kitchen, and a bath. It fits the County's "interior of existing dwelling" category (§ 400.4.A) and Anne Arundel's "within the principal dwelling" category. In the City it currently requires a property-specific ordinance; Ordinance 24-408 approved a three-unit R-8 conversion that included 1,560 sq ft of basement space.
• An attached ADU is a new addition or a partitioned wing that shares a wall or roof with the main house. The County processes it as an addition under § 400.4.A with the same one-third/2,000 sq ft cap; Anne Arundel counts a breezeway connection as attached.
• A garage conversion turns an existing attached or detached garage into living space. Anne Arundel lists it explicitly. The County treats a detached garage as an accessory building, so it needs the OAH special hearing. In the City, a garage is not a carriage house, so § 15-504 does not reach it.
• A detached ADU is a new backyard cottage or a converted freestanding outbuilding. County detached units go through OAH with the 800/1,200 sq ft caps; Anne Arundel caps them at 800 sq ft or 50% of the main house; the City allows only pre-2017 carriage-house conversions today.

Detached units behind rowhouses and alley access

A rowhouse lot gets no help from HB 1466, so a detached unit behind a City rowhouse depends on Bill 26-0195 or a successor passing. In Baltimore Brew's September 22, 2026 report, Dorsey said he sees "no problem with... where the only access to a new unit is from an alley."

Two existing City rules still bite. Article 32 § 1-306 excludes any alley perimeter from the definition of "frontage," and the subdivision regulations prohibit new lots that front on alleys. Neither stops an accessory unit on the same lot, and the state law bars the City from banning conversion of an accessory structure whose only car access is from an alley.

Fire access is the harder physical constraint. The City requires automatic residential sprinklers in every new one- or two-family dwelling, and fire-apparatus access roads must be at least 20 feet wide with 13.5 feet of vertical clearance. Existing Baltimore alleys can be as narrow as 10 feet. Fire apparatus must reach within 150 feet of all exterior walls unless the building is fully sprinklered or other conditions apply, and an unrated exterior wall needs 5 feet of fire separation from the lot line. Budget for sprinklers on any new detached unit in the City.

How to permit an ADU step by step

In Baltimore City, everything now runs through the Accela-based ePermits portal DHCD launched February 3, 2025, backed by the One-Stop Permit Center kiosk at 417 E Fayette Street (Mon–Fri, 8:30 AM–3:30 PM). Sequence the work this way:

1. Get a zoning verification letter from the Office of the Zoning Administrator confirming your district, overlays, and whether the use is permitted, conditional, or absent. If it is conditional, file with the Board of Municipal and Zoning Appeals (BMZA) or the council first; BMZA fees are $100 for a simple variance, $200 complex, $300 for a conditional use.
2. If the property sits in a local historic district, obtain a CHAP Authorization to Proceed before the building permit can issue (details in the next section).
3. Hire licensed contractors. One- and two-family construction requires a Maryland Home Improvement Commission (MHIC) contractor; electrical, plumbing, mechanical, and gas work require licensed trade contractors, and each must be registered in the DHCD permits database before you add them to an application.
4. Prepare the drawings. DHCD's guidance lists first and second floor plans, a site plan, a ground-floor demolition plan, a cross-section detail, and building elevations. Additions or new construction under 600 sq ft need scaled residential drawings; over 600 sq ft triggers ePlans review covering architectural, structural, electrical, mechanical, and plumbing sheets.
5. Apply online: create an account, pick the permit category, add applicant/owner/contractor contacts, upload drawings, pay, then monitor review tasks. An ADU typically needs the One- and Two-Family Combo Permit, a Use and Occupancy Permit for the change in use, and separate trade permits.
6. Respond to plan review. DHCD's published targets are 1–6 weeks for initial review and 1–3 weeks per resubmittal. A pre-submittal meeting costs $50 per half hour, and a free 20-minute examiner meeting is available once the application is in review.
7. Schedule inspections through ePermits as framing, rough-in, and finish work complete.
8. Close out with the Use and Occupancy permit ($45 per use per building), which is what lets you legally occupy or rent the unit.

The 2024 building code fee schedule in Baltimore City Code § 109 sets the plan-review application at $125 when construction documents are required, new building permits at $10 per 1,000 cubic feet (minimum $150), additions at the same rate with a $75 minimum, alterations at $0.30 per sq ft of affected floor area (minimum $50), and a 5% Building Code Permit Tax on the final permit cost.

Real-world timing has been worse than the targets. DHCD reported 8,600 pending permits and an 86-day average in October 2025, then said its initial-review backlog fell from more than 1,700 applications in May 2025 to 68 by February 5, 2026.

Baltimore County's PAI path

An interior or addition apartment needs a Use Permit application with a $100 fee and a Declaration of Understanding recorded in County Land Records. Upload the validated copy to the application about 7–14 days later.

A detached unit adds a Special Hearing request and a public OAH hearing, with the DOU and any conditions recorded afterward. The use permit renews every two years. Building-side fees effective July 1, 2026 include a $75 residential application fee and a $280 building-area fee for new one- and two-family construction.

Dimensional standards: size, height, setbacks and lot coverage

The numbers below are the caps in force today. After a compliant ordinance passes, the lot-size, setback and parking limits cannot be tighter than the state ceilings, though a local square-footage cap still can be.

For a basement or other interior unit, Baltimore County allows the lesser of one-third of the dwelling's floor area or 2,000 sq ft, and it may not have separate gas or electric meters. Anne Arundel requires only that an internal unit be smaller than the principal dwelling. The City has no interior ADU category, so no cap exists; property-specific ordinances have approved basement units of about 1,560 sq ft.

For an attached addition, the County applies the same one-third/2,000 sq ft rule and its district yard requirements. In the City, an addition over 600 sq ft crosses into full ePlans review, and CHAP guidelines in historic districts push additions to a secondary elevation.

For a garage conversion or new detached unit, the standards are the tightest:

• Baltimore County: 800 sq ft on lots under an acre, 1,200 sq ft at an acre or more; 15-foot height limit; 2.5-foot rear and side setbacks; accessory buildings limited to rear yards and 40% of the rear yard.
• Anne Arundel County: lesser of 800 sq ft or 50% of the main house; district accessory-structure setbacks with no variance toward neighboring residential lots; one ADU per lot; separate entrance required; same street address as the main house, designated "Unit B."
• Baltimore City: 15-foot height and 50%-of-required-rear-yard coverage for any accessory structure under § 15-501; a converted carriage house may not grow more than 20% in height or footprint; new dwellings need sprinklers and 5 feet of fire separation for unrated walls.

After local adoption, the state limits that bind are the lot-size rule (no minimum larger than the principal dwelling's) and the setback rule (side and rear no stricter than the existing accessory-structure numbers, 2.5 feet in the County). The 75% figure caps what can qualify as an ADU rather than obliging a locality to allow that much, so a tighter local square-footage cap can stand.

Historic districts and CHAP review

If your property sits in one of Baltimore City's local historic districts or is a local landmark, every piece of exterior work needs a CHAP Authorization to Proceed (ATP) before DHCD can issue a building permit. The ATP application and Article 6 § 8-2 cover alteration of exterior features, exterior excavation, construction of exterior structures or fences, and exterior demolition. A basement conversion with no exterior change avoids CHAP; a new backyard unit, a rear addition, or a new egress window does not. National Register-only districts do not trigger review unless they are also locally designated.

The count of covered districts differs by city source: the CHAP landing page says 38 neighborhoods and 200+ landmarks, while the board profile says 33 districts and 182 landmarks covering 12,000+ properties. The district maps include Bolton Hill, Canton, Charles Village/Abell, Federal Hill, Fells Point, Hampden, Locust Point, Mount Vernon, Remington, Reservoir Hill, Union Square, Upper Fells Point, and Woodberry, among others. Much of the rowhouse stock investors target is on that list.

Staff review versus a commission hearing

Minor work that does not significantly change appearance or remove historic fabric can be approved by CHAP's Executive Director, and an ATP is often issued within 48 hours of a complete application. If staff has not issued an ATP within 11 days, § 8-5 requires a public hearing notice. New construction, substantial additions, and demolition go to the full Commission, which meets monthly on the second Tuesday at 1:00 PM in the Phoebe Stanton Boardroom at 417 E. Fayette Street; complete materials are due 25 calendar days before the hearing, the hearing falls 10–45 days after posting, and the Commission has 21 days after the hearing to rule under § 8-6. An ATP expires one year after issuance if you have not pulled the permit.

CHAP's design guidelines tell you what the Commission will look for. For accessory structures: "Locate new garages, sheds, and other accessory structures in rear yards, or in other areas where they may be less visible," and "Design new accessory structures to complement the scale, form, orientation, materials, and details of the primary building." For additions: "Place additions on a secondary elevation" and keep them "compatible in massing, height, form, and scale." New construction must keep floor-to-floor heights within 10% of adjacent historic buildings.

CHAP publishes no ADU-specific denial rate, and no annual report with staff-versus-commission approval percentages turned up. The closest data point is the Commission's unanimous rejection of a proposed apartment building in Woodberry in November 2020 and again in February 2021, which was a large project, not an ADU. Note what the state law does and does not do here. Its covenant provision expressly does not reach restrictions on use for property listed in or eligible for the Maryland Register of Historic Properties, so a landmark house gets no relief from a recorded restriction. CHAP review itself is a local historic-preservation process, and the zoning mandate still applies to the lot.

Utilities, tap fees and stormwater costs in Baltimore

Since October 1, 2025, HB 1466 has barred a utility from requiring a separate water or sewer connection, or charging a connection fee, when the existing connection can support the ADU, and it lets you elect a shared meter under Chapter 197. DPW keeps the authority to decide whether capacity is adequate and to impose conditions if it is not.

Baltimore City water and sewer

DPW's available FY2026 and FY2027 materials do not provide an adopted per-diameter tap-fee schedule. The DPW miscellaneous fee document circulated only as a public draft dated January 24, 2025, is no longer posted on the DPW site, and did not list a tap fee; it does propose a DPW inspection fee of 9% of the construction cost estimate for water and sewer connections. For a confirmed quote on a new tap, you have to call DPW's Utility Enterprise permit office. What the building code does set, under § 109, is $25 for a new or replacement water service pipe, $25 for a sanitary connection, and $50 per utility for on-site water, sanitary, or stormwater work on one- and two-family dwellings.

If you do add a separate meter, the recurring charges the Board of Estimates approved in the FY25–FY27 rate schedule are:

• Meter size | FY2026 water | FY2026 sewer | FY2027 water | FY2027 sewer
• 5/8" | $16.07 | $15.15 | $17.52 | $16.51
• 3/4" | $28.87 | $27.24 | $31.47 | $29.69
• 1" | $64.14 | $60.52 | $69.91 | $65.97
• 1-1/2" | $112.23 | $105.86 | $122.33 | $115.39
• 2" | $256.51 | $241.94 | $279.60 | $263.71

A second 5/8" meter therefore adds $31.22 a month in FY2026 and $34.03 in FY2027 before any usage, plus an account management fee of $5.31 per bill (FY2026) rising to $5.79 (FY2027). Volumetric rates are $4.46 per CCF for water and $13.18 for sewer in FY2026, rising to $4.86 and $14.37 in FY2027. Both water and sewer rates rise 9% in each fiscal year.

Separate meter or shared meter?

Baltimore County answers this for you: interior apartments may not have separate gas or electric meters, and detached units may not have separate meters or water/sewer service unless OAH finds it necessary. In the City, the state law makes a shared meter your election. If you share and pass water costs to the tenant, Article 13 § 7-3 requires an express written lease provision, designation of the tenant as an MPIA designee, and a description of the allocation method with the prior 12-month average monthly cost. Under Maryland's Real Property § 8-212.4, a ratio utility billing (RUBS) clause is unenforceable unless you disclose the last two utility bills, the allocation method, the prior-year average monthly bill, and dispute information in writing. Either way, DPW holds the legal owner responsible for the account.

Electrical service upgrades run through the same permit schedule: $25 for a 0–100A service, $30 for 100–200A, and $5 per plumbing fixture. Clarksville Construction's August 2025 Maryland cost guide puts the plumbing and electrical scope of a basement ADU, sub-panel included, at $20,000–$45,000 on top of finish work.

Stormwater triggers and fees

Land disturbance of 5,000 sq ft or more requires a full stormwater management and erosion-control plan through DPW's Plans Review and Inspection Section. Under 5,000 sq ft but more than 100 cubic yards of cut and fill requires an erosion-control plan only.

Article 7 § 21-6 exempts single-family detached dwellings disturbing 2,500 sq ft or less and charges a small-project fee between 2,500 and 5,000 sq ft. Whether a detached ADU counts as a "single-family detached dwelling" for that exemption is unresolved in city guidance.

Any net increase in impervious area on a redevelopment site must meet new-development environmental site design standards under § 23-7. The DPW draft schedule prices an SWM concept review at $500 and a full plan review under two acres at $2,500.

The annual stormwater fee under Article 27 § 3-2 is tiered by impervious area: $52 a year up to 820 sq ft, $78 from 820 to 1,500 sq ft, and $156 above 1,500 sq ft. A DPW FY2025 rate page states monthly figures that annualize higher ($57.60, $86.40, $172.80), and the discrepancy is unresolved. A 600 sq ft cottage plus a path can push a rowhouse lot up a tier.

Baltimore County charges are simpler to pin down: a $575 water and $875 sewer connection charge for a 5/8" meter, plus an 8% public works inspection fee on the public portion of the work.

Renting your ADU legally in Baltimore

In Baltimore County you cannot rent an accessory apartment to an unrelated tenant at all under current rules; the occupants must be family. Everything in this section therefore applies to City ADUs, Anne Arundel ADUs, and whatever the County adopts after October 1, 2026.

Registration and licensing inspections

A rented ADU on an owner-occupied lot is a non-owner-occupied dwelling unit under Article 13 § 5-1, so it needs annual registration by January 1 and a rental license, with no exemption because you live next door. "Owner-occupied" means your single Homestead Tax Credit residence under § 4-1, and you get only one in the City. Registration costs $30 per unit per year for one- and two-unit properties.

The license itself lasts two years. Under § 5-6, you must register the unit and pay the fees. You also need a passing inspection and lead compliance.

The inspection must come from a Maryland-licensed home inspector who has registered with DHCD, be no more than 90 days old at application, and cover 100% of units for properties with nine or fewer. DHCD's inspector checklist covers railings on four-plus riser steps, GFI protection, working smoke and CO alarms, non-leaking plumbing, operable heat, and proper basement bedroom egress. Failing to post the license draws a $250 citation under the Strengthening Renters' Safety Act effective January 1, 2026.

Lead paint

Any pre-1978 rental unit must be registered with MDE at $75 per unit, renewed every two years by December 31, and hold a current lead certificate before the City issues a rental license. A basement or carriage-house conversion in a 1920 rowhouse is a pre-1978 unit even if every finish is new. The certificate types in MDE's factsheet are Full Risk Reduction (dust test in a vacant unit), Modified Risk Reduction (within 30 days of a defect notice), Lead-Free (ends future registration and inspection), and Limited Lead-Free (interior only, valid two years). For pre-1950 units, the City requires you to show the tenant the risk-reduction certificate before move-in.

Check who signed your certificate. Maryland suspended Green Environmental's inspection license in 2025 and voided roughly 1,500 lead-free certificates, and penalties reach $25,000 per violation.

HOA and covenant restrictions

HB 1466 bars deeds, covenants, and HOA rules from unreasonably limiting ADU construction or rental, which matters most in Baltimore County and Anne Arundel subdivisions. The same section expressly leaves short-term rental bans in place.

Short-term rental or long-term lease?

Long-term lease. A City STR license under Article 15, Subtitle 48 is issued only for the host's permanent residence, defined as the unit where the owner lives at least 180 days a year, with a limit of one permanent residence per host, and DHCD is issuing no new unhosted licenses. A detached or separately addressed ADU is not your permanent residence, so it cannot get a new license. The only opening is a hosted arrangement where the ADU itself is your primary residence and you rent rooms in it, which inverts the investment.

If you find a lawful STR structure anyway, the $200 biennial license comes with a 9.5% hotel tax on gross receipts. Airbnb remits it for stays of 89 nights or fewer. An unlicensed host draws a $500 citation, and continued violation is a misdemeanor at up to $500 a day.

The Jillian and Lindsay Wiener STR Safety Act adds statewide fire-equipment and annual inspection requirements from October 1, 2026. Anne Arundel conditions STR use of either unit on owner-occupancy under § 18-10-124(7). A 12-month lease at the rents in the next section avoids all of it.

What an ADU costs and what it returns in Baltimore

Baltimore-area contractors quoted the following ranges in 2025–2026, and the spread within each type is mostly about finish level, structural surprises, and whether design and permitting are included:

• ADU type | Baltimore-area range | Sources
• Basement conversion | $80,000–$200,000 for a legal unit with kitchen, bath, egress, and fire separation | Top Notch Contractors $85,000–$140,000; Clarksville Construction $80,000–$200,000 plus $8,000–$25,000 design and permitting
• Garage conversion | $75,000–$160,000 | Top Notch $95,000–$160,000 with permits through CO; Clarksville $75,000–$150,000; RemodelerIQ typical $103,618 for 600 sq ft
• Attached addition | $85–$249 per sq ft; in-law suites $46,000–$250,000 | Angi $46,000–$104,500; Clarksville $100,000–$250,000
• New detached cottage | $150,000–$300,000+ | Top Notch $180,000–$300,000+; Baltimore Banner $150,000–$350,000; Clarksville $120,000–$300,000+ plus $15,000–$40,000 site prep

The state's own 2024 ADU Market Assessment found 32% of surveyed builders reporting costs above $150,000 and 32% under $100,000. One 380 sq ft Silver Spring garage conversion finished in 2022 came in around $255,000, so the top of these ranges is not a ceiling.

On the income side, HUD's FY2027 Small Area Fair Market Rents, effective October 1, 2026, put a one-bedroom at $1,570 in Hampden (21211), $1,590 in Federal Hill (21230), $1,380 in Canton (21224), $1,570 in Towson (21204), and $1,430 in Catonsville (21228). Market listings track close: Zumper's citywide one-bedroom median was $1,199 on September 20, 2026, Hampden ran $1,400 in June, and Towson ran $1,910 in July. The Banner's March 2026 reporting cited one Maryland ADU renting for about $1,400 a month.

Worked example: carriage house behind a Hampden rowhouse

Take a rowhouse in Hampden with a 600 sq ft brick carriage house on the alley that predates June 5, 2017, the one detached configuration Baltimore City permits today. Hampden is a local historic district, so exterior work needs a CHAP ATP. If a conversion keeps the existing shell and its exterior changes do not significantly alter the building's appearance or remove historic fabric, it may qualify for staff review rather than a Commission hearing.

City fees on the building side, using the § 109 schedule: $125 plan-review application, $180 alteration permit (600 sq ft at $0.30), $45 Use and Occupancy, $30 for a 100–200A electrical service, $25 water service, $25 sanitary connection, and $30 for six plumbing fixtures at $5 each. That comes to $460 before the 5% permit tax, or about $483.

Plan for the published 1–6 week initial review plus one 1–3 week resubmittal cycle, so roughly 2–9 weeks of review, and remember the 86-day average DHCD reported in October 2025. Sprinklers apply to new dwellings, and DPW's capacity determination governs whether the existing tap suffices under HB 1466.

Construction lands in the garage-conversion band, $75,000–$160,000. At the FY2027 one-bedroom SAFMR of $1,570 for 21211, gross rent is $18,840 a year, from which you subtract $30 registration, the biennial $75 MDE lead fee, a $52–$156 stormwater tier, insurance, and vacancy. On a $110,000 all-in conversion, that gross equals about 17% of cost before expenses; on $160,000 it is under 12%.

A basement conversion under the same rowhouse costs $80,000–$200,000 and rents in the same one-bedroom band, but it needs a property-specific council ordinance until Bill 26-0195 or its successor passes.

Drawbacks and common reasons ADU projects get denied

Owner-occupancy is a major constraint for investors, and it is a Baltimore County problem more than a City one. The County permit requires you to live on site, restricts occupants to family, terminates on sale, and renews every two years. Those conditions prevent the unit from carrying unrestricted rental rights to the next owner. Anne Arundel ties owner-occupancy only to STR use, and the City's Article 32 has no such rule.

Parking, another common project constraint, has been mostly disarmed here: the City eliminated minimums by Ordinance 25-064, Anne Arundel repealed its ADU space requirement in 2023, and the state now caps any requirement at one space outside a 0.75-mile transit radius. Site access can still stop a project because a 10-foot alley cannot satisfy the 20-foot fire-apparatus access standard.

The other reasons projects die in Baltimore:

• No zoning basis in the City: if your lot has no pre-2017 carriage house, a plan reviewer has nothing in Article 32 to approve against until the council acts.
• Rowhouse exclusion from HB 1466, which leaves R-5 through R-10 owners dependent on local legislation that stalled in December 2025.
• CHAP review in a local historic district, where new construction goes to a monthly Commission hearing with a 25-day submission lead time and a one-year ATP expiration.
• Size caps that shrink the unit below what rents well: 800 sq ft for detached units in both counties on typical lots, and one-third of the house for a County interior unit.
• Utility capacity findings by DPW, or an OAH refusal to allow separate service in the County.
• Sprinkler and fire-separation costs on any new City dwelling, and a 5,000 sq ft disturbance threshold that pulls larger sites into full stormwater plan review.
• HOA covenants that ban short-term rentals, which the state law leaves intact.
• A lead certificate issued by a suspended inspector, which blocks the rental license until you re-test.

Permit backlog is a schedule risk rather than a denial, but a 60-day-plus wait was reported by more than a third of applicants in a February 2023 Banner survey and the October 2025 average hit 86 days.

Insuring a Baltimore ADU

A rented ADU is not covered by the homeowners policy on the main house. Steadily's ADU insurance page states it directly: "Your homeowners policy will not cover a guest house used as a rental, and the rental activity adds liability the main policy is not built for." How the unit gets written depends on how it attaches to the main building and whether it has its own lease.

• An ADU that shares a wall or roof with the primary structure sits under Coverage A (Dwelling).
• An unrented detached unit can fall under Coverage B (Other Structures), which is 10% of the dwelling limit and too small for a $150,000 cottage.
• A unit rented under a separate lease "typically requires treatment as a second dwelling or separate policy." Steadily notes that an endorsement on the primary dwelling policy is often cheaper than a standalone policy, though a fully rented ADU sometimes needs the standalone version.

For a rented unit, a DP3 open-peril form with replacement cost valuation is the form to ask for. A DP1 pays actual cash value on named perils and will not respond to a burst supply line behind a basement kitchenette.

Every Steadily landlord policy includes liability, with options from $100K to $1M+ per occurrence. Loss of rental income pays up to 12 months of fair rental value, capped by a sub-limit tied to dwelling coverage, when a covered peril makes the unit uninhabitable.

Flood from rising water is excluded and needs a separate policy, which matters for a basement unit near the harbor. During construction, Steadily writes vacant and renovation properties, so the carriage house is insurable before the first tenant signs.

If you do land a hosted STR license, Steadily writes short-term rental policies in all 50 states, and the STR form prices differently from a long-term landlord policy. Landlord insurance in Maryland carries a state median premium of $1,149.50 a year. The national average across property types is about $1,478. Older rowhomes and carriage houses can push landlord insurance in Baltimore above that state median because of building age.

A $100,000 dwelling limit, roughly the rebuild cost of a small conversion, typically runs $500–$1,000 a year. Raising the deductible from $1,000 to $5,000 trims premium about 12–15%.

Get a quote in minutes at quote.steadily.com, no phone call required; enter the property address, and the form pulls construction data from public records so you can add the ADU as a second dwelling or an endorsement before the Use and Occupancy permit issues.

FAQ

These answers summarize the legality, cost, permitting, rental, and historic-review rules that Baltimore-area owners ask about most often.

Can I build an ADU in Maryland?

Yes on any lot zoned for a single-family detached house, once your local government adopts the ordinance HB 1466 required by October 1, 2026. Anne Arundel County has allowed ADUs as a conditional use since May 2023, Baltimore County allows family-occupied accessory apartments, and Baltimore City had not enacted a compliant ordinance as of September 28, 2026. Rowhouse and townhouse lots are outside the state mandate.

How much does an ADU cost in Baltimore?

Baltimore-area contractors quoted $80,000–$200,000 for a basement conversion, $75,000–$160,000 for a garage conversion, and $150,000–$300,000 or more for a new detached cottage in 2025–2026, with design and permitting adding $8,000–$25,000 when not included. City permit fees for a 600 sq ft conversion come to roughly $483 under the § 109 schedule.

What is one drawback of an ADU?

An ADU adds rental registration and lead compliance for a pre-1978 unit. It also needs a landlord insurance endorsement or policy. In Baltimore County, the current family-occupancy rule prevents you from renting the unit to an unrelated tenant.

Does Anne Arundel County allow ADUs?

Yes, as a conditional use in the RA, RLD, R1, R2, R5, R10, and R15 districts under § 18-10-124, with no minimum lot size, no added parking, one ADU per lot, and a detached-unit cap of 800 sq ft or 50% of the main house. R22 and RCA zones exclude them.

How do Baltimore City and Baltimore County ADU rules differ?

The County has a working permit process with hard limits: owner- and family-occupancy, a 15-foot height cap, 2.5-foot setbacks, 800 sq ft for detached units on sub-acre lots, and an OAH hearing for anything detached. The City has no ADU use category at all, so outside a pre-2017 carriage-house conversion you need a property-specific council ordinance, though the City imposes no owner-occupancy rule and no parking minimum.

Can I put a detached ADU behind a rowhouse?

Today only by converting a carriage house that stood on June 5, 2017. HB 1466 does not cover rowhouse lots, and Bill 26-0195, which would allow new detached units behind rowhouses by right, remained pending in committee in late September 2026. The City also requires sprinklers in every new one- or two-family dwelling, and fire-apparatus access rules still apply.

Does a historic district block an ADU?

Not automatically, but in a local CHAP district any exterior work needs an Authorization to Proceed before the permit issues. Minor work can clear staff in 48 hours; new construction goes to a monthly Commission hearing with materials due 25 days ahead. Properties on or eligible for the Maryland Register of Historic Properties lose the state law's covenant protection, so a recorded restriction can still bar the unit, but the zoning mandate itself still reaches the lot.

Do I need to register a rented ADU, and can I list it on Airbnb?

Yes to registration: $30 a year with the City and a two-year rental license backed by a third-party inspection. Any pre-1978 unit also needs a $75 biennial MDE lead registration.

Airbnb is effectively closed for a detached unit because a City STR license requires the unit to be your own permanent residence, and DHCD issues no new unhosted licenses. Plan on a long-term lease.