Buyer Education · September 7, 2026 · 9 min read
Last Tuesday I stood in a Bel Air driveway with a couple in their fifties. Nice half-acre lot. They wanted to know if they could build a small cottage out back for her mother, who's 78 and still sharp but tired of shoveling snow in Pennsylvania.
"We want her close," the wife said, "but not that close."
I laughed. She didn't.
This conversation is happening everywhere right now. Adult children are looking at their parents' fixed incomes, their own full nests, and a housing market that punishes people who sell and move. The solution sounds simple: build an accessory dwelling unit, keep grandma nearby but independent, and maybe help with daycare or dinners when it makes sense.
Except Maryland zoning doesn't make it simple. And most people don't realize that until they've already fallen in love with the idea.
So here's the real story on ADUs in our corner of the world—what's legal, what it costs, and whether your property can actually handle one.
An accessory dwelling unit is a second, smaller residence on a single-family lot. It has its own kitchen, bathroom, sleeping area, and entrance. It's not a basement apartment your landlord rents out without permits. It's not your grown son living above the garage with a hot plate.
It's a separate home. And that distinction matters to the county.
Some places call them granny flats, in-law suites, or backyard cottages. Maryland zoning codes just call them accessory dwelling units, and whether you're allowed to build one depends entirely on where your house sits.
I work across Cecil, Harford, Baltimore County, Baltimore City, and a handful of other jurisdictions. Every single one treats ADUs differently.
Harford County allows them by special exception in most residential zones, but you'll need to prove the ADU won't change the character of the neighborhood. That's code-talk for "your neighbors get to weigh in." Minimum lot size is usually one acre, and the ADU can't exceed 800 square feet or 35% of the primary dwelling's footprint, whichever is smaller. Harford County's zoning code spells it out in Section 267, if you're the type who reads before bed.
Baltimore County updated its ADU rules a few years ago and made them slightly easier. You can build on lots as small as 6,000 square feet in some zones, and the process is mostly administrative if you're doing an attached or interior conversion. Detached units still require more hoops. Cap is 1,000 square feet. Check the Baltimore County Department of Permits, Approvals and Inspections for current applications.
Cecil County is quieter on this front. ADUs are allowed in agricultural zones under certain conditions, but suburban residential? You're mostly out of luck unless you want to spend months at zoning hearings.
Baltimore City is more flexible than the counties, which surprises people. Accessory structures are common, and if you're in a neighborhood zoned R-8 or similar, an ADU conversion might sail through faster than you think.
If you're shopping for a home specifically because you want to add an ADU later, tell your realtor that before you tour. I've walked properties with families who didn't mention it until we were under contract, and then we discovered the lot was 0.4 acres in a zone that requires 0.5. Game over.
I'm a Maryland realtor, not a builder, but I ask a lot of questions at settlement tables and I hear the numbers.
A detached 600-square-foot ADU—new construction, sitework, utilities, permits—runs anywhere from $150,000 to $250,000 in our market right now. That's assuming no major surprises with septic, water, or electric service.
An attached addition or garage conversion? Maybe $80,000 to $150,000, depending on how much plumbing and HVAC you're adding.
A basement conversion is the cheapest route if your foundation allows it. Figure $40,000 to $80,000 if you're adding egress windows, a kitchen, and a second bath. But then it's not really a separate dwelling in the eyes of most counties—it's just a really nice basement.
Financing is tricky. Most lenders won't give you a construction loan for an ADU the way they would for a primary home addition. You're looking at a home equity line of credit, a cash-out refinance, or savings. The Federal Housing Administration has kicked around ideas for ADU-specific loan products, but we're not there yet.
Permitting in Maryland takes forever.
I had a client in Harford County wait eleven months from application to approval for a detached ADU. Eleven. The holdup? The health department needed a perc test for a second septic system, then the planning commission wanted a stormwater management plan, then a neighbor filed a protest about setbacks.
That was before a single shovel hit dirt.
If you're planning this for an aging parent, start earlier than you think. Don't wait until mom falls and can't manage stairs anymore. By the time the unit is habitable, she might need more care than an independent cottage provides.
Sometimes. Maybe.
An ADU in a hot market like Columbia or Ellicott City, where rental demand is strong and lots are big? Yeah, that's a selling point. I can market it as rental income potential or multi-gen living, and buyers will pay attention.
An ADU in a rural part of Cecil County where most buyers want peace, quiet, and no tenants? It might actually narrow your buyer pool. Some people see a second unit and assume headaches.
And here's the thing appraisers struggle with: is it an ADU or is it a second home on one lot? If your county allowed it by special exception, does that transfer to the next owner automatically, or do they need to reapply? Title companies ask these questions at settlement, and if the answers aren't clean, your buyer's lender might walk.
I always recommend having that conversation with a local Maryland realtor before you build. We know what sells in your ZIP code.
Let's say you're shopping for a home in Harford County or Baltimore County and you want a property with an existing ADU—maybe you plan to rent it, or maybe your father-in-law is moving in.
Good luck getting conventional financing if the ADU is rented.
Most lenders treat it as a two-unit property, which means different loan products, higher down payments, and tighter debt-to-income ratios. FHA won't touch a property with rental income from an ADU unless you can document two years of landlord history. Freddie Mac has some flexibility for owner-occupied properties with ADUs, but your lender needs to know what they're doing.
If you're looking at properties with ADUs, make sure your lender pre-qualifies you for that specific scenario. Don't assume your pre-approval letter covers it.
And if you're working with a Maryland realtor who doesn't ask about the ADU's legal status, rental history, and septic capacity before you write an offer, find a different realtor. Those details torpedo deals at inspection.
I've seen families pour money into ADU plans only to hit a wall they didn't see coming.
Septic systems are the biggest killer in Harford and Cecil Counties. If your home is on well and septic, adding a second dwelling often means upgrading or adding capacity. The county health department won't sign off otherwise, and a new septic system can cost $15,000 to $30,000 before you even start the cottage.
Setbacks are the second dream-killer. Most counties require 20- to 30-foot setbacks from property lines for a detached structure. If your lot is narrow or your house sits close to the sides, you might not have room even if your acreage technically qualifies.
Homeowners' associations are the third. If you're in a planned community, your ADU dreams are probably dead on arrival. HOAs in Maryland almost universally prohibit accessory structures that look like separate homes, no matter what the county allows.
I don't want to sound like I'm talking people out of ADUs. When the zoning aligns, the lot supports it, and the family has realistic expectations, they're wonderful.
I have clients in Fallston who built a 700-square-foot cottage for the husband's dad three years ago. He's 82 now, still drives, still cooks his own breakfast. They see him most days, but he has his own space and his own front door. When they sell someday—hopefully years from now—that ADU will be a huge selling point because the lot is gorgeous and the build quality is solid.
But they started the process two years before he moved in. They knew the zoning. They budgeted for delays. And they didn't treat it like a DIY project.
If you're thinking about an ADU for aging parents, here's the order of operations:
Check your county's zoning. Don't trust Facebook groups or your neighbor's cousin. Call the planning office or pull the code yourself. Maryland Department of Planning has county contacts.
Walk your lot with a surveyor. Find out if your setbacks, lot size, and existing structures leave room for what you're imagining.
Talk to your septic company or water/sewer provider. If you're on septic, this is the conversation that ends dreams or greenlights them.
Get pre-construction cost estimates from at least two builders. And add 20% for the stuff they didn't think of.
Talk to a Maryland realtor about resale. Not because you're selling tomorrow, but because it's smart to know whether you're adding value or complexity. If you're looking at homes for sale in Harford County, Baltimore County, or anywhere in my coverage area, I'm happy to talk through the ADU angle before you make an offer. Reach out here.
Loop in an elder law attorney if your parent is contributing financially or will have ownership interest. Medicaid look-back rules and estate planning matter, and I've seen families create legal tangles they didn't mean to.
Here's what I ask families at the kitchen table: are you building this because it's the best housing solution for your parent, or because it's the least uncomfortable conversation?
Sometimes the ADU is perfect. Sometimes assisted living is the right call and nobody wants to say it. Sometimes the parent just needs a good ranch home ten minutes away, and that's cheaper and simpler than construction.
I spent twenty years in education before I became a realtor. I've had hard conversations with parents about their kids' futures. This is the same skill set, just flipped. If you're not sure, talk it through with someone who's seen it play out both ways.
I've been that person for a lot of families across Cecil, Harford, and Baltimore counties. If you're exploring multi-generational living, downsizing for a parent, or trying to figure out what makes sense in this market, let's talk. Check current listings here or reach out. I'll tell you what I actually think, not what sounds nice.
And if you're under contract already and just found out your buyer's lender won't finance the ADU you thought was an asset, call me. I've worked through worse.
Katrina Kirton Sherrod, REALTOR® · Samson Properties · Licensed in MD, DC, PA & DE · 443-616-9770 · Katrina@kkstherealtor.com
“Owning a home is a keystone of wealth — both financial affluence and emotional security.” — Suze Orman