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KEY TAKEAWAY
Accessory dwelling units are a simple idea.
Take a property with a single-family home and add a smaller, independent home. It might be inside the existing house, part of an addition or a separate structure in the backyard. It could provide a place for an aging parent, an adult child, a renter or simply someone looking for a smaller home.
Simple enough.
Then zoning gets involved.
How large can the ADU be? Where can it go? How far does it need to be from the property line? Does it need another parking space? Can an existing garage be converted? Does it count toward density?
Suddenly, the little house in the backyard has a regulatory agenda.
Maryland decided last year that, whatever the answers to those questions might be locally, ADUs need to be a realistic option.
What Maryland Actually Did
In 2025, the General Assembly passed HB 1466/SB 891, making it State policy to promote and encourage ADUs as one way to help meet Maryland’s housing needs. The law took effect October 1, 2025, and gives local governments with zoning authority until October 1, 2026 to adopt compliant local laws.
The State did not write one ADU ordinance that applies everywhere. Instead, it established a baseline.
An ADU can be attached to the main house, created through a conversion or located in a separate accessory structure. Under the State definition, it can be up to 75% of the size of the primary single-family detached home. Local rules must exclude ADUs from density calculations and measures that otherwise limit residential growth on the property. The law also limits how local governments can use parking requirements as a barrier to ADUs.
Local governments still have plenty to figure out. Building codes still apply. So do health and safety requirements and adequate public facilities rules. The State law also leaves room for certain local development standards.
So Maryland didn’t eliminate local control over ADUs. It narrowed the range of ways local regulations can make them difficult, or effectively impossible, to build. And now the counties have to translate that into actual zoning regulations.
Montgomery County Already Has ADUs. That Doesn’t Mean Its Work Is Done.
Montgomery County starts from an interesting position because it already allows ADUs.
Unfortunately, “we already have an ordinance” is not the same thing as “we’re done.”
When County staff compared the existing regulations with the new State requirements, they identified several places where the two don’t line up, including where ADUs are allowed, size requirements, density calculations, setbacks and off-street parking.
That led to Zoning Text Amendment 26-06, which would revise the County’s existing ADU standards to align with State law.
The proposed changes are not just housekeeping. Montgomery County currently uses different size limits for attached and detached ADUs. ZTA 26-06 would instead use the State’s 75% standard. It would also revise setback, parking, allowable zone and density provisions.
“A regulation can say that an ADU is permitted, but if the rules leave nowhere to put one, that permission doesn’t mean very much to the homeowner standing in the backyard with a tape measure.”
Those details matter. A regulation can say that an ADU is permitted, but if the combination of lot size, setbacks, parking and dimensional requirements leaves nowhere to put one, that permission doesn’t mean very much to the homeowner standing in the backyard with a tape measure.
Montgomery County’s task, then, isn’t really to decide whether to allow ADUs. Maryland has already answered that question. It’s figuring out how much of the County’s existing regulatory framework can stay.
Prince George’s County Has a Different Starting Point
Prince George’s County is taking a broader approach.
The County has been working through how the State law should be implemented locally, including both zoning and related regulations that affect how an ADU can actually be created and used.
That work has led to CB-074-2026, the County’s proposed zoning legislation for ADUs. The bill would add ADU definitions to the zoning ordinance, establish where they are permitted and set development standards intended to comply with State law. The Planning Board supported the proposal with amendments, and the bill was introduced in September.
A separate measure, CB-092-2026, addresses issues outside the zoning ordinance, including rental requirements, short-term rentals, tree and woodland requirements, impervious surface limits and individual sewage disposal systems. Even a very small house can generate a surprisingly large amount of legislation.
That process looks different from Montgomery County’s because the starting point is different. Montgomery County is largely reworking an established ADU program to fit the new State framework. Prince George’s County is using the State mandate to build out a broader local framework.
Same State law. Different zoning history. Different implementation process.
That is pretty typical of land use reform.
“ADUs Are Legal” Is Not the Same as “I Can Build One Here”
This is probably the most important part for homeowners.
Once the counties finish updating their regulations, it will be tempting to summarize all of this as: Maryland legalized ADUs. That’s not quite right.
The State has required local governments to allow them under a new set of ground rules. It has also removed or limited some of the regulatory barriers that can make an ADU impractical.
But an individual property still has to work. A detached ADU may still need to meet setbacks. A conversion still must comply with building and life safety codes. Water and sewer capacity can matter. Environmental constraints can matter. Historic preservation may matter. And the size and configuration of the existing house and lot will still determine what is physically possible.
So if you own a house in Bethesda, Silver Spring, Hyattsville or College Park, the useful question isn’t “Can I have an ADU?” It’s “What kind of ADU can I actually create on this property?”
That is where zoning becomes property-specific.
One Small Unit, but a Bigger Shift
ADUs are not going to solve Maryland’s housing shortage. They are, however, part of a broader conversation about the “missing middle” - housing options that fall somewhere between a traditional single family house and a larger apartment building. Duplexes, triplexes, small multifamily buildings and ADUs can all fit into that broader conversation, although an ADU is probably the smallest version of the idea.
In this case, we’re talking about adding one additional home to a property that already has one.
Not exactly a skyline-changing event.
But that’s partly the point. An ADU can add housing without assembling land, rezoning a site or building a large development. In some cases, the change may barely be noticeable from the street. One house becomes two homes. Multiply that opportunity across thousands of properties, and those small changes can start to matter.
ADUs can also serve housing needs that are surprisingly difficult to accommodate in conventional development: an older parent who wants to live near family without sharing the same kitchen, an adult child who needs some independence, a homeowner looking for rental income, or someone who simply wants a smaller place to live in an established neighborhood. That flexibility is part of the appeal.
It is also why the details of these county ordinances matter. If the rules are too restrictive, very few property owners will actually use them. If the regulations are clear and workable, ADUs become another modest way of adding housing where homes already exist.
WHAT THIS MEANS FOR YOUR PROJECT
The State Set the Direction. The Details Are Still Local.
Maryland has made the larger policy decision: local governments need to make room for ADUs.
Montgomery County is adjusting an existing program to meet that requirement. Prince George’s County is building out its local framework through a broader legislative process. Both have until October 1.
For homeowners, that doesn’t mean October 2 will suddenly be Build a Cottage in Your Backyard Day. The final local rules will still matter. So will the property. Setbacks, building codes, utilities, environmental conditions and the existing house itself aren’t disappearing.
But the starting point is changing. Instead of asking whether local zoning should allow another small home on a single-family property, Maryland has largely answered that question.
Yes. Now figure out how.
And that’s where Montgomery and Prince George’s Counties are today.
For a homeowner considering an ADU, the question becomes more specific: What do the new rules allow me to do on my property? As usual with zoning, that’s where things get interesting.
CLOSING SECTION
The Practical Next Step
If you’re considering an ADU, don’t start with a generic floor plan. Start with the property. The final county rules, lot dimensions, existing improvements, utilities and other constraints will determine which options are actually worth exploring.
Maryland has changed the starting point. The next question is what that change means on your lot.
RELATED READING
- Can You Add an ADU to Your Property?
- What Does “By-Right” Actually Mean?
- Land Use Strategy & Early Project Planning
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