Maryland is quickly becoming a hotspot for Accessory Dwelling Units (ADUs) as homeowners look for smarter, more flexible ways to use their property. With a mix of dense urban neighborhoods, coastal communities, and wide-open rural areas, Maryland’s ADU laws are some of the most varied on the East Coast, making it essential to understand the rules in your specific county or city before you start planning.
Unlike states with a single statewide ADU policy, Maryland’s ADU regulations are governed locally, and each county sets its own standards for size, placement, permitting, parking, and what qualifies as a legal ADU. The good news? Many of Maryland’s largest counties have adopted modern ADU ordinances that make adding a backyard cottage, in-law suite, or garage apartment far easier than it was just a few years ago.
Whether you’re exploring ADUs for multigenerational living, rental income, or simply more space, this guide breaks down every key rule you need to know across Maryland. Zook Cabins is here to help you navigate Maryland’s ADU requirements with clarity, accuracy, and a homeowner-friendly approach.
Are ADUs Allowed in Maryland?
Yes, ADUs are allowed in Maryland, but the rules depend heavily on the county or municipality you live in. Maryland does not have a single statewide ADU law, so every jurisdiction sets its own standards for where ADUs can be built, how large they can be, and what permits are required. This means your experience can vary dramatically across the state: places like Montgomery County, Prince George’s County, Howard County, and Anne Arundel County have some of the most flexible ADU policies in Maryland, while more rural counties may still have tighter restrictions or specific zoning requirements you must meet.
In most areas where ADUs are permitted, homeowners can build attached, interior, or detached units as long as they follow local zoning rules, safety codes, and property-size requirements. Because Maryland’s ADU policies aren’t uniform, the smartest first step is checking your county’s ordinance so you know exactly what’s allowed on your property.
However, it’s essential to note that the state is rolling out ADU regulations, which most counties and cities will need to adopt by the end of 2026. You can find more information about the statewide ADU laws on the Maryland Planning Department.
If you’re thinking about adding an ADU in Maryland, this guide breaks down everything county by county, making it easier to understand your options no matter where you live.
What Is Considered An ADU in Maryland?
In Maryland, an Accessory Dwelling Unit (ADU) is defined as a secondary, self-contained residential unit located on the same property as a primary home. Even though each county writes its own zoning code, most Maryland jurisdictions treat an ADU the same way: it must function like a small, independent home while still remaining clearly secondary to the main dwelling.
A legal ADU in Maryland typically includes:
- A separate entrance (interior or exterior)
- Its own kitchen or kitchenette
- A private bathroom
- A dedicated living/sleeping area
- Full compliance with residential building code, fire safety, and utility standards
ADUs in Maryland can be built in several forms such as: finished basements, garage or attic conversions, attached additions, or detached backyard units as long as they meet the county’s size limits, setback requirements, and permitting rules. The biggest thing to remember is that Maryland does not regulate ADUs at the state level, so what counts as an ADU in one county may have slightly different specifications in another.
Can Park Model ADUs Be Used As ADUs?
Park Model homes can be used as ADUs in Maryland, but only when they meet full residential building-code standards. Maryland does not automatically treat park models (which are often built to RV standards) as legal ADUs. To qualify as an ADU, the structure must be installed on a permanent foundation, connected to utilities according to local code, and compliant with the International Residential Code (IRC) adopted by the county.
This means a traditional RV-style park model on wheels will not be accepted as a legal dwelling in most Maryland counties. However, modular park model style units that are built to residential code and delivered as modular homes can be approved and permitted just like any other detached ADU.
So, if you want a park model look with legal ADU status in Maryland, choose a builder that produces code-compliant modular units, not RV-certified models.
Can Log Cabins Be Used As An ADU?
Yes, log cabins can be used as ADUs in Maryland, as long as they meet the same building and zoning requirements as any other detached accessory dwelling unit. Maryland doesn’t regulate ADUs at the state level, so counties decide what is allowed, but across most jurisdictions, the key requirement is that the structure must be built to the International Residential Code (IRC) and placed on a permanent foundation.
A log cabin ADU must function as a fully self-contained dwelling with its own kitchen, bathroom, sleeping space, and proper utility connections. As long as the cabin is code-compliant, permitted, and sized within the county’s ADU limits, Maryland counties like Montgomery, Prince George’s, Howard, Frederick, and Anne Arundel generally allow it.
The only type of log cabin that cannot be used as an ADU is one built to recreational or campground standards (such as park-model or RV-certified log cabins). To be legal in Maryland, your cabin must be built as a residential structure, not a temporary or movable unit.
Can Modern Cabins Be Used As An ADU?
Yes, modern cabins can be used as ADUs in Maryland as long as they are built to residential code and meet the zoning rules of the county where the property is located. Maryland doesn’t restrict ADUs by architectural style, so a modern cabin, contemporary modular design, or minimalist backyard studio is fully allowed if it functions as a complete dwelling. This means the unit must have its own kitchen, bathroom, living space, proper utility hookups, and be placed on a permanent, code-compliant foundation.
Since Maryland regulates ADUs at the local level, the exact size limits and placement rules vary by county. However, counties like Montgomery, Prince George’s, Howard, Frederick, and Anne Arundel all permit detached ADUs when they follow the International Residential Code (IRC) and meet zoning standards such as setbacks and lot size.
As long as your modern cabin is built as a true residential structure it can be approved and used legally as an ADU in most Maryland jurisdictions.
What is the Difference Between a Prefab ADU & a Modular ADU?
A prefab ADU is a broad term that describes any accessory dwelling unit built off-site in a factory, while a modular ADU is a specific type of prefab that meets full residential building-code standards. In other words, all modular ADUs are prefab, but not all prefab units qualify as modular. Prefab can include sheds, tiny homes, RV-style park models, and panelized builds, but many of these do not meet the International Residential Code (IRC) required for a legal ADU in Maryland.
A modular ADU, however, is constructed in code-certified modules, inspected at the factory, shipped to your property, and installed on a permanent foundation, making it a fully legal residential dwelling. For Maryland homeowners, this distinction matters: if you want an ADU that can be permitted, lived in year-round, and recognized as a true dwelling unit, a modular ADU is the option that will meet every requirement.
What is the Minimum Size for an Accessory Dwelling Unit?
Maryland does not have a single statewide minimum size for ADUs; the requirement depends on the county or municipality. However, most Maryland jurisdictions follow a similar baseline: an ADU must be large enough to function as a safe, self-contained dwelling under the International Residential Code (IRC). In practical terms, this usually means no smaller than 220–300 sq. ft., since that’s the minimum space needed for a legal living area, kitchen, bathroom, and proper egress.
Counties with established ADU ordinances like Montgomery, Prince George’s, Anne Arundel, Howard, and Frederick typically set their minimums around this same range or simply require the ADU to meet all IRC standards without specifying an exact square footage.
So while Maryland doesn’t set one size for the whole state, you can safely expect that any permitted ADU must be at least a few hundred square feet and fully code-compliant to qualify as a legal dwelling.
Can My ADU be Bigger Than My House?
No, your ADU cannot be bigger than your primary house in Maryland. Across nearly all Maryland counties that allow ADUs, the secondary unit must remain clearly subordinate to the main dwelling. While each county sets its own rules, the pattern is consistent: ADUs have a maximum size limit and can never exceed the square footage of the primary home.
Most Maryland jurisdictions use one of these size standards:
- A fixed maximum size (commonly 800–1,200 sq. ft., depending on the county)
- A percentage of the main home’s size (often 40–50% of the primary dwelling)
- Whichever is smaller, to ensure the ADU stays secondary
Counties like Montgomery, Prince George’s, Howard, Frederick, and Anne Arundel all follow some form of this rule.
So while you have flexibility to build a comfortable, fully functional ADU, it cannot be larger than your main house anywhere in Maryland. This keeps the ADU classified as an accessory structure rather than a second primary residence.
How Close To My House Can I Build An ADU?
In Maryland, the distance your ADU must maintain from your main home depends entirely on local zoning setbacks, since the state does not use a single statewide rule. Every county applies its own accessory-structure setback standards, which typically control how close an ADU can sit to the primary dwelling, the side yard, and the rear property line.
For example, counties like Montgomery and Anne Arundel require detached ADUs to follow the same setback rules as sheds or garages in their zoning district, often meaning several feet of separation for fire safety, access, and utility placement. Because these requirements vary from one jurisdiction to the next, the exact distance can change depending on your county and zoning classification.
The simplest way to determine how close your ADU can be built is to check your county’s accessory-structure setback chart, which dictates the minimum spacing between buildings on your lot.
Do You Need A Permit For An ADU in Maryland?
Yes, you need a permit to build an ADU in Maryland, no matter which county you live in. Because Maryland does not have a statewide ADU law, each county controls its own permitting process, but the pattern is the same everywhere: an ADU is considered a legal dwelling unit, so it requires full review and approval before construction can begin. This typically includes a zoning review, a building permit, and approvals for electrical, plumbing, mechanical, and foundation work. Counties with established ADU ordinances, outline clear steps for submitting site plans, floor plans, utility connections, and code-compliant construction details.
Even if your ADU is built off-site (like a modular unit), you still must obtain permits for placement, installation, and all utility hookups. Skipping permits can lead to fines, stop-work orders, or denial of occupancy. For Maryland homeowners, the safest and fastest approach is checking with your county’s permitting department early, so you know exactly which documents and inspections your ADU project will require.
Are There Any Incentives or Grants for ADUs in Maryland?
Maryland doesn’t have a dedicated ADU-only grant yet, but there are programs that can help fund parts of an ADU project. Many homeowners use broader housing incentives from the Maryland Department of Housing and Community Development (DHCD), which offer assistance for renovations, safety upgrades, accessibility improvements, and exterior work, costs that often overlap with building or converting space for an ADU.
Some counties and cities also offer financial incentives in designated revitalization zones, where creating additional housing is encouraged. While none of these programs are marketed specifically for ADUs, your project may still qualify if it improves your property or adds long-term housing. For Maryland homeowners looking to offset costs, these state and local programs can be a helpful starting point.
Are Zook Cabin’s ADUs Built to Code?
Yes, every Zook Cabins ADU is built to full residential code and designed to meet Maryland’s local requirements. Our team has years of experience working with ADUs, so each unit is engineered with county-specific building codes, safety standards, and zoning rules in mind. From the foundation to the finishes, we make sure your ADU meets the regulations needed for a smooth approval process.
Can an ADU Have Multiple Bedrooms and Bathrooms?
Yes, an ADU in Maryland can include multiple bedrooms and bathrooms as long as it meets the size requirements set by local officials. You can find the specific rules for your area in the city or county section below.
Many jurisdictions allow one to two bedrooms and one to two bathrooms as long as the ADU fits within their size limits. This makes models such as the Grove, Luna, and A-Frame viable options in several Maryland municipalities for those interested in an ADU with multiple bedrooms and bathrooms.
Are ADUs A Good Investment?
Yes, ADUs are considered an excellent investment for most homeowners. A well-built ADU can bring in reliable rental income, significantly increase your property value, and give you long-term flexibility for guests, aging family members, or even downsizing onto your own property. In many markets, ADUs boost a home’s value by 10%–30%, and because the land is already paid for, ADU rentals often deliver some of the highest ROI in residential real estate. Whether you want passive income, extra space, or added equity, an ADU offers one of the strongest financial returns of any home improvement.
What Counties in Maryland Allow ADUs?
Does Allegany County Allow ADUs?
Allegany County does allow ADUs, but the rules are much more limited compared to other parts of Maryland. The county only permits accessory dwelling units in a few specific zoning districts, mainly business and industrial zones, while most residential areas do not offer a simple by-right option for adding a secondary unit. Homeowners must verify their zoning district before planning a basement conversion, backyard cottage, or garage apartment.
If your property qualifies, the ADU must follow the county’s accessory structure standards, including required setbacks, proper utility connections, and full compliance with local building codes. Since Allegany County’s ADU regulations are more restrictive than neighboring counties, checking your parcel’s zoning and contacting the county permitting office is an essential first step.
Does Anne Arundel County Allow ADUs?
Yes, Anne Arundel County allows ADUs, and it has one of the most homeowner-friendly ADU policies in Maryland. In 2023, the county updated its zoning code to make ADUs easier to build across most residential districts. Homeowners can add one accessory dwelling unit per lot, whether it is attached, internal, or fully detached. Detached ADUs must stay within the county’s size limits, which cap the structure at the smaller of 800 square feet or 50 percent of the primary home’s living area.
ADUs also need a separate entrance, must share the same address as the main house, and require proper permits along with full building-code compliance. No additional parking is required for an ADU, and most residential zones now support these units unless the property falls within the R22 district or certain Chesapeake Bay Critical Area zones. For homeowners in Anne Arundel County, these updated rules create a clear and accessible path to adding new living space, rental income, or multigenerational housing.
Does Baltimore County Allow ADUs?
Yes, Baltimore County allows ADUs, but its rules are more restrictive than those of many other Maryland counties. ADUs are permitted on owner-occupied properties, meaning the homeowner must live in the main dwelling for the ADU to be legal. The county also sets size limits based on lot size: properties under one acre can build an ADU up to 800 square feet, while lots one acre or larger may go up to 1,200 square feet.
The ADU must function as a complete dwelling with its own kitchen, bathroom, and living space, and it must meet all residential building-code standards through the county’s permitting process. Because of the owner-occupancy rule and the size-based limits, Baltimore County’s ADU regulations have more conditions than other nearby jurisdictions, so homeowners should review their lot size and zoning before moving forward with an ADU project.
Does Calvert County Allow ADUs?
Yes, Calvert County allows ADUs, and the county offers a clear path for homeowners who want to add an accessory apartment or detached living space on their property. ADUs can be attached to the main home or built as a standalone structure, as long as the project meets local zoning rules and receives the proper permits. Any ADU over 200 square feet requires a building permit, and detached units must follow Calvert County’s accessory-structure standards, including setbacks and utility requirements. Recent zoning updates have also expanded the allowable size for detached units, giving homeowners more flexibility to build larger, fully functional ADUs on qualifying lots.
All ADUs must comply with standard residential building codes, including plumbing, electrical, septic or sewer connections, and any required site or stormwater reviews. For homeowners in Calvert County, the combination of updated zoning and straightforward permitting makes adding an ADU a realistic option for extra space or long-term housing.
Does Caroline County Allow ADUs?
Yes, Caroline County allows ADUs, and the county has some of the most detailed size and placement rules in the region. Homeowners can build one ADU per property, either within the main home or as a detached structure, as long as the unit falls between 400 and 1,000 square feet and never exceeds 50 percent of the primary dwelling. Detached ADUs must be placed in the side or rear yard and located within 100 feet of the main home, ensuring the structure remains clearly secondary.
The county also requires both the ADU and the primary house to stay under common ownership and share utilities, and the design must remain visually subordinate to the main home. ADUs require an official application, and nearby property owners are notified, which may trigger additional review if objections are submitted. With these guidelines in place, Caroline County offers a defined pathway for homeowners looking to create a legal accessory dwelling on their property.
Does Carroll County Allow ADUs?
Yes, Carroll County allows ADUs, and the county offers a structured path for both attached and detached accessory dwelling units. Homeowners are limited to one ADU per lot, and the property must be owner-occupied, meaning you must live in either the main home or the ADU. Attached ADUs are capped at 800 square feet or one-third of the main home’s living area and may include no more than two bedrooms.
Detached ADUs must follow the county’s accessory-structure rules and meet all building, health, and safety codes, even though the zoning code does not list a specific size limit for detached units. As long as the ADU is fully self-contained with its own kitchen, bathroom, and living space, and the project passes the county’s permitting and inspection process, Carroll County provides a clear legal pathway for adding an accessory dwelling to your property.
Does Cecil County Allow ADUs?
Cecil County does not currently have a clear, county-wide ADU ordinance, which limits its regulations and makes them less predictable compared to those of many other Maryland counties. While the county follows the International Residential Code for all dwellings and accessory structures, its zoning rules do not explicitly list ADUs as a permitted use in most residential districts. This means that adding a secondary unit, such as a converted basement, garage apartment, or detached cottage, may require a case-by-case review rather than a straightforward ADU approval.
Homeowners interested in building an ADU will need to check their specific zoning district and work directly with the county’s Planning and Zoning Division to determine whether a secondary dwelling is allowed on their property. Because ADUs are not formally recognized across all zones, Cecil County remains one of the more restrictive areas in Maryland for homeowners seeking to add an accessory dwelling unit.
Does Charles County Allow ADUs?
Yes, Charles County allows ADUs, and the county has a well-defined ordinance that makes both attached and detached accessory apartments possible for homeowners. An ADU in Charles County can be built inside the main home or as a standalone structure, as long as it remains clearly secondary to the primary dwelling. The county requires each ADU to be a complete living space with its own kitchen, bathroom, and sleeping area, and sets the minimum size at 300 square feet while capping the unit at no more than 50 percent of the main home’s total floor area.
Only one ADU is permitted per lot, and all projects must meet health department standards for water and sewage, which is especially important for homes on septic systems. Detached ADUs must also follow local accessory-structure rules and maintain the residential appearance of the property. With these guidelines in place, Charles County provides a straightforward path for adding a legal, code-compliant ADU to your property.
Does Dorchester County Allow ADUs?
Yes, Dorchester County allows ADUs, but the county’s rules are among the more restrictive in Maryland. Under its zoning code, ADUs are permitted only as “accessory apartments” located inside an owner-occupied single-family home. This means detached backyard cottages, garage apartments, or standalone tiny homes are not clearly allowed under current regulations. The ADU must remain smaller than the main home, capped at either 800 square feet or one-third of the primary dwelling’s living area, whichever is less.
Dorchester County also requires the property to maintain its single-family appearance, and either the main home or the accessory apartment must be owner-occupied. Because of these limitations, homeowners planning an ADU in Dorchester County should focus on interior conversions and verify zoning requirements with the county before starting their project.
Does Frederick County Allow ADUs?
Yes, Frederick County allows ADUs, and the county has one of the most clearly defined and accessible ADU policies in Maryland. Homeowners can build an attached, interior, or detached unit as long as the ADU remains no larger than half the size of the primary dwelling and meets all residential building-code requirements. Smaller ADUs under 1,000 square feet can be approved through a standard building permit, making the process straightforward without the need for a special exception.
Frederick County does require owner-occupancy, meaning the property owner must live in either the main home or the ADU, and detached units must follow accessory-structure rules and include at least one additional parking space. With these guidelines, Frederick County offers a clear and workable pathway for homeowners to add basement apartments, garage conversions, or backyard cottages as legal, code-compliant ADUs.
Does Garrett County Allow ADUs?
Garrett County does allow ADUs, and recent zoning updates have made the process far more accessible for homeowners. The county now permits attached, interior, and detached ADUs as long as the secondary unit stays smaller than the main home, typically capped at around half of the primary dwelling’s size. ADUs must also follow local zoning rules for setbacks, height, and placement, and meet the same building-code standards as any residential structure.
These updates were part of Garrett County’s housing-affordability efforts, giving residents a clear path to adding basement apartments, garage conversions, or small backyard cottages. While specific lot requirements can vary by zoning district, the overall guidelines are consistent enough to make Garrett County one of Western Maryland’s more ADU-friendly areas.
Does Harford County Allow ADUs?
Harford County does allow ADUs, but the rules here are more limited compared to many other Maryland counties. ADUs are only permitted inside or directly attached to the main home, meaning standalone backyard cottages or detached tiny homes are not allowed under current zoning. The county sets clear size rules, allowing units between 300 square feet and no more than 1,500 square feet or 50 percent of the home’s livable space, whichever is smaller.
ADUs can include up to two bedrooms, must have their own full living and kitchen setup, and require the property owner to live on-site in either the main house or the ADU. These regulations create a straightforward path for basement apartments, attic conversions, or over-garage suites, but they do not support detached accessory homes.
Does Howard County Allow ADUs?
Howard County does allow ADUs, but the rules here are stricter and more limited than in many nearby counties. Under the current zoning code, homeowners can only build attached or interior accessory apartments, meaning the ADU must be located within or physically connected to the main home. Detached ADUs are still very difficult to approve and generally require special conditions, which limit the ability to build backyard cottages or standalone small homes.
Howard County has been reviewing a zoning amendment that would expand ADU options, but until that update is finalized, most homeowners must stick to basement conversions, over-garage apartments, or additions that stay within the footprint of the primary residence.
Does Kent County Allow ADUs?
Kent County does allow ADUs, and the county’s zoning rules make it relatively straightforward for homeowners to add a small secondary unit on their property. ADUs are permitted as long as they remain clearly subordinate to the main home in both size and appearance, and the property owner must live on-site in either the primary residence or the ADU. The county also requires that any separate entrance be located on the side or rear of the home rather than facing the street, and at least one off-street parking space must be provided.
ADUs in Kent County can be rented long-term but cannot be sold as separate properties, and all units must meet standard residential building- and health-code requirements. Overall, the county offers a clear and workable pathway for homeowners interested in creating additional living space or long-term rental income.
Does Montgomery County Allow ADUs?
Montgomery County does allow ADUs, and it’s one of the most ADU-friendly counties in Maryland, thanks to its clear, well-established rules. Homeowners can build either an attached ADU, such as a basement or garage conversion, or a fully detached ADU as long as it meets zoning limits. Detached units can be up to 1,200 square feet but must also stay within 50 percent of the main home’s footprint and no more than 10 percent of the lot area, which keeps them scaled appropriately for residential neighborhoods.
Every ADU must follow standard requirements for setbacks, height, utilities, and building code, and rental units must be licensed through the county. With these guidelines, Montgomery County provides one of the smoothest pathways in the state for adding a backyard cottage, rental suite, or multigenerational living space.
Does Prince George’s County Allow ADUs?
Prince George’s County currently does not allow ADUs, making it one of the few Maryland counties where new accessory units are still prohibited under local zoning. The county’s planning department states that ADUs are not permitted, and homeowners cannot build detached cottages, basement apartments, or garage conversions as legal secondary dwellings at this time. However, the county has formed an ADU Task Force to study new zoning updates, which means change is likely on the horizon. Early discussions point toward eventual legalization, but until new legislation is adopted, residents must rely on existing single-family zoning or explore other housing options. For now, Prince George’s County remains off-limits for new ADU construction, though future updates may open the door to more flexible housing choices.
Does Queen Anne’s County Allow ADUs?
Queen Anne’s County does allow ADUs, and the county offers a clear, workable set of rules for anyone looking to add a secondary unit on their property. Homeowners can build one ADU per single-family lot, either inside the main home or as part of an approved accessory structure, as long as the unit stays 1,500 square feet or smaller. Properties on septic require additional review from the county health department to ensure the system can support the added dwelling, and all ADUs must meet building, zoning, and utility standards before being approved.
Queen Anne’s County also requires owner-occupancy, meaning you must live in either the ADU or the main home. With these straightforward guidelines, the county makes it feasible to add a basement apartment, a converted garage, or a small detached cottage while staying fully code-compliant.
Does St. Mary’s County Allow ADUs?
St. Mary’s County does allow ADUs, and its regulations are detailed but straightforward once you know the basics. Homeowners can create an ADU inside the main home or within a detached accessory structure, as long as the unit stays within size limits: at least 300 square feet but no larger than 40 percent of the home’s total floor area or 900 square feet, whichever is smaller. Detached ADUs follow the same maximum size cap. Only one ADU is permitted per lot, and St. Mary’s County now requires owner-occupancy, meaning you
Does Somerset County Allow ADUs?
Somerset County does allow ADUs, and the county gives homeowners several flexible ways to create a secondary unit on their property. You can convert an existing space like a basement or attic, add onto your home, build a detached structure, or turn an accessory building such as a garage into a fully equipped living space. Only one ADU is permitted per lot, and the unit must remain clearly secondary in size and appearance to the main home. Every ADU must include its own kitchen, bathroom, and sleeping area and meet county requirements for zoning, building code, and health standards, especially for properties using septic.
Because Somerset County regulates ADUs through its zoning ordinance, homeowners should expect to go through a formal permit process, but the rules are clear enough to make adding a rental unit or in-law suite a realistic option.
Does Talbot County Allow ADUs?
Talbot County does allow ADUs, and the county’s zoning rules outline a clear path for adding a secondary dwelling on a residential lot. Homeowners can build an attached or interior ADU within the main house, or a detached ADU in a separate accessory structure, as long as it stays within 100 feet of the primary home and uses the same sewage system.
Detached ADUs in rural or septic-dependent areas are limited to 900 square feet, and every property is restricted to one ADU total. The county also prohibits ADUs from being subdivided or sold separately, keeping them legally tied to the main residence. With these guidelines, Talbot County offers a workable framework for basement apartments, garage conversions, or small standalone cottages that meet local code and environmental requirements.
Does Washington County Allow ADUs?
Washington County does allow ADUs, and its updated zoning rules make it possible to build attached, interior, or fully detached units on a single-family lot. Homeowners can add one ADU per property, with most units capped between 1,000 and 1,200 square feet or no more than 75 percent of the primary home’s floor area. ADUs must follow all standard zoning and building-code requirements, including setbacks, height limits, utility connections, and lot-coverage rules.
The county also requires that the ADU stay under the same ownership as the main home, meaning it cannot be subdivided or sold separately, and it cannot be used for short-term rentals. With these guidelines, Washington County gives residents a clear and workable framework for adding a backyard cottage, basement apartment, or in-law suite that fits local zoning rules.
Does Wicomico County Allow ADUs?
Wicomico County does allow ADUs, and the county’s zoning ordinance outlines a clear but structured path for adding a secondary dwelling on a residential lot. Homeowners can create one ADU per property through an interior conversion, an attached addition, or in some cases a detached accessory structure, as long as the ADU stays smaller than the primary home. Most ADUs cannot exceed 50 percent of the main home’s living area, and detached units must follow strict setback and lot-coverage limits.
In environmentally sensitive “critical area” zones, the rules tighten further, requiring the ADU to be within 100 feet of the main house, capped at 900 square feet, and connected to the same sewage system. While Wicomico County’s guidelines are more detailed than in some parts of Maryland, they still provide a workable pathway for building a basement apartment, garage conversion, or small backyard cottage that meets zoning and environmental standards.
Does Worcester County Allow ADUs?
Worcester County does not have a clear, county-wide ADU ordinance, which means ADUs are not universally permitted across all residential zones. Instead, the county treats accessory apartments as a use that may be allowed only in certain zoning districts or through conditional approval, depending on the property’s location and underlying land-use rules.
Some homeowners may be able to add an ADU if their zoning district specifically lists accessory apartments as an approved use, but others may find that a secondary dwelling is not permitted without a special exception. Because Worcester County has no unified ADU policy, homeowners need to check their zoning designation and work directly with the county’s planning department to determine whether a basement apartment, garage conversion, or backyard cottage can legally be built on their lot.
Accessory Dwelling Unit Requirements by Municipalities
Does Baltimore Allow ADUs?
Baltimore does not currently allow ADUs under a clear, citywide ordinance, which means most homeowners cannot add a backyard cottage, garage apartment, or basement suite as a legal secondary dwelling. Existing zoning makes ADUs difficult to permit without special approval, and the city has not yet adopted the broader ADU-friendly rules seen in other Maryland jurisdictions.
That said, state law now requires all Maryland municipalities to create standardized ADU regulations by 2026, so Baltimore is expected to update its zoning code in the near future. Until those changes take effect, homeowners should assume ADUs are restricted and confirm options directly with the city’s Department of Housing and Community Development.
Does Columbia Allow ADUs?
Columbia does allow ADUs, but that permission comes through Howard County’s zoning code, since Columbia is a planned community rather than an incorporated city with its own laws. Under the county’s updated ADU regulations, homeowners can build attached, interior, or detached ADUs as long as they meet key requirements like size limits, setback rules, and building-code compliance.
Many detached units are capped at around 900 square feet or 50 percent of the main home’s floor area, and every ADU must go through the county’s permitting process. With these updated rules, Columbia residents now have a clearer pathway to add a basement apartment, garage conversion, or small backyard cottage that fits local zoning standards.
Does Germantown Allow ADUs?
Germantown does allow ADUs because it falls under Montgomery County’s ADU-friendly zoning rules. Homeowners can build attached units like basement suites or garage conversions, as well as fully detached backyard cottages, as long as the ADU stays within the county’s size and zoning limits. Detached ADUs must be no larger than the smallest of three measurements: 10 percent of the lot area, 50 percent of the main home’s footprint, or 1,200 square feet.
All ADUs must also follow standard building-code requirements, including setbacks, height limits, utility connections, and proper permitting. With these flexible guidelines, Germantown residents have one of the smoothest pathways in Maryland to add rental space, multigenerational housing, or a small, code-compliant backyard home.
To get the process started, reach out to Montgomery County’s Department of Permitting Services.
Does Silver Spring Allow ADUs?
Silver Spring does allow ADUs, since all ADU rules in this area are governed by Montgomery County’s zoning code. Homeowners can add either an attached ADU, such as a basement apartment or garage conversion, or a detached backyard cottage as long as the unit meets the county’s size, setback, and permitting requirements. Detached ADUs are capped at the smallest of three limits: 1,200 square feet, 10 percent of the lot area, or 50 percent of the main home’s footprint, ensuring the ADU stays secondary to the primary residence.
Every ADU must follow standard building-code rules and go through the county’s permit and licensing process. With these guidelines, Silver Spring offers a clear, predictable path for homeowners wanting to build multigenerational housing, long-term rental space, or a small detached ADU.
To get the process started, reach out to Montgomery County’s Department of Permitting Services.
Does Frederick Allow ADUs?
Frederick does allow ADUs, and the city follows the same ADU-friendly framework established by Frederick County. Homeowners can build an interior, attached, or detached ADU as long as the secondary unit remains smaller than the main home, typically capped at no more than 50 percent of the primary dwelling’s size. Smaller ADUs under 1,000 square feet can be approved through a simple building permit, which makes the process far easier than in many nearby jurisdictions.
Detached ADUs must also follow accessory-structure rules for setbacks, parking, and utilities, and every ADU must meet standard residential building-code requirements. With this combination of clear standards and streamlined permitting, Frederick offers one of the most accessible pathways in Maryland for adding a legal basement apartment, garage conversion, or backyard cottage.
To get the process started, please contact the city’s Building and Permits Department.
Does Rockville Allow ADUs?
Rockville does allow ADUs, but only in the form of attached units under the city’s updated zoning rules. Homeowners can add a basement apartment, in-law suite, or other attached ADU as long as the unit stays under 50 percent of the primary home’s total floor area and has its own entrance. The city requires owner-occupancy, meaning the homeowner must live in either the ADU or the main house, and some projects must meet off-street parking requirements unless the property is located near a Metro station.
Detached ADUs are not yet permitted by right in Rockville, and a separate proposal to allow backyard cottages is still under review. For now, residents looking to build a legal ADU must stick to attached configurations that comply with the city’s size, entrance, parking, and permitting standards.
If you would like to check the status of their detached ADU regulations, contact Community Planning and Development Services.
Does Gaithersburg Allow ADUs?
Gaithersburg does allow ADUs, since all ADU regulations in the city follow Montgomery County’s ADU-friendly zoning code. Homeowners can add an attached ADU, convert an interior space like a basement or garage, or build a detached backyard cottage as long as the unit stays within county size limits. Detached ADUs must be no larger than 1,200 square feet, 10 percent of the lot area, or 50 percent of the main home’s footprint.
Every ADU must also meet Montgomery County’s standard requirements for setbacks, utilities, building code, and permitting. With these flexible and well-established rules, Gaithersburg gives homeowners a clear path to create additional rental space, multigenerational housing, or a small, code-compliant backyard home.
To ensure compliance, check with Planning Services.
Does Bowie Allow ADUs?
Bowie does not currently have a clear zoning ordinance that allows ADUs, and the city’s published codes focus only on sheds and basic accessory structures, not secondary dwellings meant for full-time living. Because of that, homeowners should assume that basement apartments, garage conversions, and detached backyard cottages are not permitted as legal ADUs under Bowie’s current rules.
However, Maryland’s new statewide housing law will require every municipality, including Bowie, to adopt ADU-friendly regulations by 2026, so the city is expected to update its zoning code in the near future. Until these changes are officially adopted, residents should verify directly with the city’s Planning and Sustainability Department before proceeding with any ADU plans.
Does Hagerstown Allow ADUs?
Hagerstown does not currently allow ADUs, and the city’s zoning code makes that especially clear by prohibiting any detached accessory structure from being used as a living space. While accessory buildings like garages and sheds are permitted, they cannot be converted into dwellings, which effectively rules out detached ADUs and backyard cottages. Even interior conversions depend on strict zoning and building-code requirements, leaving homeowners with very limited options for creating secondary units. Statewide ADU reforms may push Hagerstown to update these rules in the coming years, but for now, residents should assume that ADUs are not permitted and confirm any potential projects directly with the city’s Planning Department.
Does Annapolis Allow ADUs?
Annapolis does allow ADUs, and the city has one of the clearest, most structured ADU programs in Maryland, thanks to its dedicated ADU Guide. Homeowners can create interior, attached, or detached ADUs as long as the unit meets zoning rules for single-family lots and stays within the city’s size limits. Detached ADUs can be up to 850 square feet of livable space unless they are built inside an existing structure, and every ADU must include a separate entrance along with standard building-code compliance. Annapolis also requires ADUs to follow accessory-building setback rules and environmental standards, which ensure the new unit fits neatly within neighborhood layouts.
While the city is currently reviewing possible updates to its ADU ordinance, the existing framework already offers a stable, predictable process for adding a basement apartment, garage suite, or small backyard cottage. This makes Annapolis one of the more accessible places in Maryland for homeowners looking to expand living space or generate extra income through a legal ADU.
If you have any questions about current ADU regulations, please contact the Planning, Zoning and Building Department.
Does College Park Allow ADUs?
College Park does not currently have a clear, citywide ordinance that explicitly allows ADUs, which makes the rules here more limited and harder to navigate than in many nearby Maryland communities. The city’s zoning code does not define ADUs as a permitted accessory use, and most guidance focuses on standard dwelling or rooming units rather than full secondary apartments. Because of this, homeowners should not assume that a basement apartment, garage conversion, or detached backyard cottage is automatically allowed.
Any project involving additional living space would require building permits, and renting to non-family members would trigger occupancy permits and inspections. Until College Park adopts a formal ADU policy, homeowners considering an ADU should confirm the rules directly with the city’s Planning and Community Development Department.
Does Salisbury Allow ADUs?
Salisbury does not currently have a fully adopted ADU ordinance, but the city is in the middle of reviewing new rules due to Maryland’s statewide ADU legislation. Right now, Salisbury’s zoning code does not formally recognize accessory dwelling units as a permitted use, which means detached or attached ADUs are not guaranteed to be approved under existing regulations. The City Council has already begun discussions about how ADUs will fit into local zoning, especially as Maryland moves toward requiring municipalities to allow them by 2026.
Until Salisbury finalizes its updated ordinance, homeowners should assume ADUs are evaluated on a case-by-case basis and may face additional review. If you’re planning an ADU project in Salisbury, check with the Infrastructure and Development Department first to confirm what is currently allowed and how upcoming rule changes may affect your plans.
Does Laurel Allow ADUs?
Laurel does allow ADUs, but the city classifies them as “accessory apartments” and sets stricter limits than many other Maryland municipalities. In most zoning districts, homeowners can add a secondary unit inside their existing home, but the ADU cannot exceed 25 percent of the primary dwelling’s floor area and must remain clearly subordinate to the main house. Detached ADUs or additions that expand the home by more than 50 percent require a special-exception review through the Board of Appeals, which adds extra time and oversight to the process.
Because of these rules, interior conversions like basement or attic apartments are the simplest path, while backyard cottages and large expansions require more approvals. Overall, Laurel provides a workable but regulated framework, making early coordination with the city’s Planning and Zoning Department essential for anyone planning an ADU.
Does Waldorf Allow ADUs?
Waldorf does not currently have a clear municipal ordinance that expressly permits ADUs, and its zoning framework is less defined than that of many other Maryland communities. Most secondary units, such as basement apartments or garage conversions, are not automatically allowed, and detached backyard cottages are generally treated as separate dwellings rather than accessory uses. Because Waldorf is an unincorporated area governed by Charles County, local ADU rules will depend on the county’s zoning code, which is still limited and does not yet offer a full, by-right ADU pathway.
This landscape is expected to change, since Maryland’s new statewide ADU law requires all jurisdictions to adopt ADU-friendly regulations by 2026. Until updated rules are adopted, homeowners should confirm requirements directly with Charles County Planning and Growth Management to determine whether their ADU idea is permissible and what approvals may be needed.
Does Glen Burnie Allow ADUs?
Glen Burnie does allow ADUs, since the community follows Anne Arundel County’s updated ADU ordinance, which is one of the clearer and more homeowner-friendly frameworks in Maryland. Under the county’s rules, homeowners can build an interior, attached, or detached ADU on most single-family lots, as long as the unit stays within the size limits and remains secondary to the main home. Detached ADUs are capped at the lesser of 800 square feet or 50 percent of the primary dwelling’s floor area, and every ADU must have its own entrance, meet full residential building-code standards, and share the same address as the main house.
The county also removed parking-space requirements, making projects easier to approve. With these consistent rules in place, Glen Burnie offers a straightforward path for adding a legal basement apartment, garage conversion, or backyard cottage.
Be sure to certify compliance with all applicable regulations with the Anne Arundel County Planning and Zoning Department.
Searching for an ADU Builder Serving Maryland?
Now that you know the ins and outs of Maryland’s ADU regulations, you’re ready for the exciting part: choosing a builder you can trust. Zook Cabins delivers across all of Maryland, from the mountains of Western Maryland to the Chesapeake Bay and the suburbs surrounding D.C. No matter where you live, getting a high-quality, code-ready ADU is simple. Our team brings years of experience, modern construction methods, and a true commitment to creating flexible living spaces that fit your lifestyle. Want to see what’s possible? Reach out to talk with a sales specialist or request a free quote. You’ll get upfront pricing, expert craftsmanship, and dedicated support from your first question all the way to move-in day.
Tiny Homes & ADU Rules by State: How Do They Compare?
Maryland is quickly becoming one of the more ADU-friendly states on the East Coast, especially with the new statewide ADU law that requires every jurisdiction to adopt clear, consistent ADU regulations by 2026. While Maryland has historically seen big differences from county to county, the state is now moving toward a unified system similar to what states like California and Oregon have already implemented. This shift means most Maryland homeowners will soon have a predictable, accessible path to add an attached, interior, or detached ADU on a single-family lot.
Instead of navigating scattered rules, Maryland’s new ADU framework establishes a baseline that applies across the state: one ADU per lot, clear size limits tied to the primary home, and full compliance with residential building code. Detached, attached, and interior ADUs will all be permitted once local zoning updates take effect. Tiny homes follow the same logic as many other states; foundation-built tiny homes can qualify as ADUs, while tiny homes on wheels are treated as RVs and cannot be used as permanent residences. And to make comparing states easier, we offer straightforward, state-by-state guides for both tiny home laws and ADU regulations, so you always know the exact rules before you build.
Overall, Maryland is positioning itself as one of the most accessible places in the Mid-Atlantic to add a small, code-compliant living space. With statewide consistency on the horizon and modern housing policies rolling out, Maryland is becoming a top choice for homeowners seeking flexible space, multigenerational living options, or a backyard home that meets all residential standards.