Yes, a garage can become an accessory dwelling unit in parts of Maryland—but the answer depends heavily on whether the garage is attached or detached and which county or municipality controls the property. Anne Arundel County expressly allows ADUs in attached or detached garages. Howard County’s current ADU guidance lists garage apartments as an example. Montgomery County recognizes apartments over garages and detached accessory structures, while Baltimore County still operates under an older accessory-apartment framework that treats detached structures differently.
Quick answer
An existing garage is not automatically a legal ADU. Once you add independent sleeping, cooking and sanitation facilities, the project can trigger ADU zoning, building permits, fire-separation, egress, plumbing/electrical/mechanical review, and sometimes rental-license or septic/well requirements.
Last verified: September 8, 2026. Maryland is in an active ADU transition ahead of the October 1, 2026 local-law deadline. This guide distinguishes current published rules from pending legislation and does not treat draft local language as final law.
1. First question: what kind of garage are you converting?
The word garage conversion hides several different zoning situations. Before checking square footage or cost, identify which one you actually have.
| Garage configuration | Why it matters |
|---|---|
| Attached garage | May be reviewed as an attached or interior ADU depending on the local code and how the new unit connects to the principal dwelling. |
| Detached garage | Usually triggers detached-ADU or accessory-structure rules, including separate setbacks, lot coverage, height and sometimes a different approval path. |
| Apartment over an attached garage | May fit an attached-ADU pathway, but access, fire separation and building-code details still matter. |
| Apartment over a detached garage | Usually behaves like a detached ADU because the dwelling unit is in a separate accessory structure. |
| Finished garage room without an independent kitchen | May be additional living space rather than an ADU, but converting garage space to habitable space can still require permits and code upgrades. |
The practical takeaway is simple: do not buy a generic “garage ADU plan” until you know how your jurisdiction classifies your exact structure. A plan that fits one county’s detached-ADU rules can fail another county’s size, setback or approval requirements.
What Maryland law says about converting an existing garage
Maryland Land Use §4-504 expressly anticipates conversion of existing accessory structures. A local legislative body may adopt ADU safety standards and may prohibit full or partial conversion of an accessory structure into an ADU if the only vehicular access to that structure is from an alley.
The same state law says local ADU side and rear setbacks may not exceed the jurisdiction’s existing accessory-structure setback requirements, while still preserving building-code, health, safety and adequate-public-facilities review. An existing garage shell therefore does not automatically become legal residential space without local approval.
2. Maryland garage-to-ADU rules by county
| Jurisdiction | Can a garage be part of an ADU path? | Important 2026 issue |
|---|---|---|
| Anne Arundel County | Yes. Current county law expressly allows an ADU in an attached or detached garage. | Detached-unit size remains a transition issue as Bill 61-26 moves through the 2026 Article 18 update. |
| Howard County | Yes. The county’s current ADU page lists garage apartments as an example and CB3-2026 allows attached and detached ADUs. | Maximum size is calculated as 75% of the exterior footprint of the principal dwelling; owner occupancy is required. |
| Montgomery County | Yes. DPS describes ADUs as including apartments over garages and points homeowners to detached-garage/accessory-structure permit information. | The county remains in transition under ZTA 26-06, so current legacy size rules and proposed 2026 changes must be separated. |
| Baltimore County | Potentially, under the legacy accessory-apartment framework. | Detached accessory apartments historically require a Special Hearing; a final HB 1466-aligned framework has not yet been verified by this site. |
| Prince George’s County | Transition—do not rely on draft criteria yet. | CB-074-2026 and companion CB-092-2026 are still moving through the county legislative process. |
3. Anne Arundel County: the clearest garage-conversion language
Anne Arundel County provides one of Maryland’s clearest current examples. The 2023 law that created the county’s present ADU framework says an ADU may be located in an attached or detached garage or in another detached structure. It also states that conversion of all or part of an existing structure into an ADU must be constructed under the permits required by county code.
For a detached structure, the county’s current public rule still lists the lesser of 800 square feet or 50% of the floor area of the principal single-family detached dwelling. That size issue is currently part of a broader 2026 transition, so do not assume the current detached cap will remain unchanged after the Article 18 update is finalized.
Real Anne Arundel zoning cases show why garage projects are not just a matter of interior remodeling. In 2026, county hearing records included proposals to convert a detached garage into an ADU and to place an ADU above a garage where setback or height relief was requested. The structure may already exist, but its location can still create zoning problems once residential use is added.
Read our Anne Arundel County ADU transition guide before sizing a detached garage conversion.
City of Annapolis: garage conversions are expressly recognized
Annapolis is a useful reminder that a municipality can have its own ADU rules. The City’s current ADU FAQ expressly says an ADU may be created by a garage conversion, attached or detached, as well as within or attached to a single-family home or as a new detached structure. If your property is inside Annapolis, check the City rule rather than assuming Anne Arundel County’s zoning process controls.
4. Howard County: garage apartments are recognized, but the footprint math matters
Howard County’s current ADU guidance explicitly lists garage apartments among common ADU examples. CB3-2026 became effective April 8, 2026 and allows homeowners to construct attached and detached ADUs or renovate existing space for an attached ADU in qualifying residential districts.
The county’s maximum-size method is unusual and should be checked before buying plans: the ADU may not exceed 75% of the exterior footprint of the principal dwelling. Howard also requires the property owner to live in either the principal dwelling or the ADU, and the county prohibits ADUs from being used as short-term rentals.
A detached garage conversion must also be reviewed against the county’s accessory-structure lot-coverage and stormwater rules. Existing walls do not make those site constraints disappear.
Check the current Howard County ADU guide for the latest enacted-rule notes and source conflicts.
5. Montgomery County: apartments over garages are already part of the ADU framework
Montgomery County’s Department of Permitting Services describes ADUs as units that can be a stand-alone backyard structure, basement apartment, addition or apartment over a garage. Its homeowner permit page specifically points ADU applicants to indoor finishing permits and to detached-garage/accessory-structure permit resources.
Under the county’s currently published legacy framework, detached ADUs remain subject to a maximum gross-floor-area formula based on the smallest of three limits: 50% of the principal-dwelling footprint, 10% of the lot area or 1,200 square feet. ZTA 26-06 is intended to change several portions of the existing framework to align with Maryland’s 2025 state law, so homeowners should distinguish the rule being administered today from the proposed replacement.
Read the Montgomery County ZTA 26-06 transition guide before committing to a garage layout.
6. Baltimore County: garage apartment rules are still tied to the legacy framework
Baltimore County’s published zoning policy still uses the terms accessory apartment and in-law apartment. Under that framework, an apartment within an existing single-family detached dwelling can proceed through the county’s Use Permit process when the required conditions are met. A detached accessory building used as an in-law apartment has historically required a Special Hearing.
This matters for garage projects because converting an attached garage or building an addition is not necessarily treated the same as turning a detached garage into a second dwelling. Baltimore County’s own zoning policy manual distinguishes principal-dwelling accessory apartments from detached accessory-building cases.
Because this site has not yet verified a final 2026 HB 1466-aligned replacement ordinance for Baltimore County, do not assume the legacy pathway will be the final rule after October 1. See our Baltimore County transition guide for the latest status.
7. Prince George’s County: wait for final 2026 text before buying garage-ADU plans
Prince George’s County is still moving through its 2026 ADU implementation process. CB-074-2026 is the principal zoning vehicle and CB-092-2026 addresses several non-zoning issues. As of this review, final enacted local criteria for garage conversions should not be inferred from draft or committee-stage material.
If your property is in Prince George’s County, the safest move is to identify the structure and collect measurements now, but avoid purchasing a prefab garage conversion package or final plan set based on draft size, setback, parking or rental assumptions. Track the Prince George’s County ADU transition here.
8. Garage-to-ADU permit checklist: what to verify before you design
A garage conversion can look simple because the shell already exists. In practice, the expensive problems often appear when the space changes from vehicle/storage use to habitable residential use.
- Confirm who controls zoning. Maryland counties do not always control incorporated municipalities. Check the exact county/city jurisdiction first.
- Classify the garage. Attached, detached, over-garage and partially connected structures may follow different ADU standards.
- Check the legal location of the existing garage. An old garage can be legally nonconforming for setback or height. Converting it to residential use can trigger a new zoning review.
- Confirm the permitted ADU size. Do not assume the garage’s existing square footage automatically becomes allowable living area.
- Get the building-permit path. Expect review of the change to habitable space and any new structural, insulation, electrical, plumbing, HVAC and energy-code work.
- Check fire separation and egress. Sleeping rooms, attached garages and independent dwelling areas can create specific life-safety requirements.
- Check septic or well capacity early. Adding a bedroom or independent dwelling on a private system can trigger Health Department review. Use our Maryland ADU Septic & Well Guide.
- Check rental licensing separately. Zoning approval to create an ADU does not automatically answer whether a rental license or short-term-rental license is required.
- Verify before construction. Ask the local permitting office to identify the currently administered code section and permit path in writing.
9. Is converting a garage cheaper than building a detached ADU?
It can be, but the existing shell is only valuable if it is suitable for residential conversion. A garage may need slab/foundation work, insulation, windows, fire separation, plumbing trenching, electrical upgrades, heating and cooling, and structural changes before it functions as a code-compliant dwelling.
In our review of published Maryland-area builder pricing, garage conversions commonly appeared below fully detached new-build ADUs, but the ranges overlap heavily once utilities and structural work are added. Use the Maryland ADU Cost Calculator & Contractor Bid Comparison rather than comparing a garage-conversion headline quote with an all-in detached ADU budget.
10. Maryland garage ADU FAQs
Can I convert an attached garage into an ADU?
Potentially, yes. The local code determines whether the project is treated as an attached/interior ADU and what entrance, fire-separation and size requirements apply. Anne Arundel expressly allows ADUs in attached garages; other jurisdictions use different classifications.
Can I convert a detached garage into an ADU?
Potentially, but detached structures usually face more site-specific zoning constraints. Anne Arundel expressly allows ADUs in detached garages. Howard permits detached ADUs. Baltimore County’s legacy system has historically required a Special Hearing for an accessory apartment in a detached accessory building.
Can I build an apartment above my garage?
In some jurisdictions, yes. Montgomery County’s own ADU materials list an apartment over a garage as an ADU example. The exact classification depends on whether the garage is attached or detached and on local height, setback, access and building-code rules.
Do I need a permit if I am not changing the outside of the garage?
Do not assume interior-only work is permit-free. Converting storage or vehicle space into independent habitable residential space can require zoning and building review even when the exterior barely changes. New plumbing, electrical, HVAC, sleeping rooms or a second dwelling unit can trigger additional permits and inspections.
Can I rent the converted garage?
Possibly, but rental rules vary. Some jurisdictions require owner occupancy or a rental license, and short-term rentals can be restricted separately. Confirm the current county/city rental rules after you confirm that the ADU itself is legal.
Does Maryland’s 75% rule mean my entire garage can become an ADU?
No. The state definition sets an ADU-size ceiling relative to the primary dwelling, but the measurement method and local implementation matter. Howard County, for example, uses 75% of the principal dwelling’s exterior footprint. Other jurisdictions are still finalizing 2026 rules. Use our Maryland 75% ADU Size Calculator & Measurement Guide before assuming a garage’s full area qualifies.
Bottom line
A garage can be one of the most practical ways to create an ADU in Maryland, but the existing building does not bypass zoning or permit review. The most important questions are whether the garage is attached or detached, how the jurisdiction classifies it, whether the structure already complies with site rules, and which 2026 ADU framework is actually in force.
Start with your jurisdiction in the Maryland County ADU Rules Tracker, then use the Property Feasibility Checker before spending money on final garage-conversion plans.
Primary sources used for this guide
- Maryland Land Use §4-504 — accessory-structure conversion, setbacks and local ADU requirements
- City of Annapolis — ADU FAQ
- Anne Arundel County — Laws of 2023, Bill 6-23
- Anne Arundel County — Residential Code Requirements
- Anne Arundel County Council — Bill 61-26
- Howard County — Accessory Dwelling Units
- Montgomery County DPS — Homeowners Permits
- Montgomery County DPS — ADU Zoning Requirements
- Montgomery County DHCA — Class 3 ADU Information Sheet
- Baltimore County — Zoning Policy Manual, Accessory Apartments
- Prince George’s County — Accessory Dwelling Units Task Force
- Maryland Department of Planning — HB 1466 FAQ
Maryland ADU Guide is maintained by Gijo John as an independent research publication. We prioritize enacted laws, county code, official legislative records and planning/permitting guidance. Source-backed corrections can be sent to gijo.j@marylandaduguide.com.