Buying a Maryland Home for an ADU: 12 Due-Diligence Checks Before You Make an Offer

Last researched: September 27, 2026.

If you are buying a Maryland home partly because you want to add an accessory dwelling unit (ADU), the question is not simply whether the backyard looks large enough. Before you make an offer, you need to know who controls the zoning, whether the property already has the type of primary dwelling required for an ADU, how much of the lot is actually buildable, and whether septic, easements, overlays, utilities or private restrictions could change the project.

Start here: run the address through the Maryland ADU Jurisdiction Finder, then use the Maryland ADU Property Feasibility Checker. The steps below explain what to verify before treating a property as “ADU-ready.”

1. Confirm who actually controls the property’s zoning

A Maryland mailing address does not always tell you which government controls land use. Some incorporated municipalities administer their own zoning, while others rely on county rules for some functions. Before comparing setbacks or ADU size limits, confirm the actual reviewing authority for the parcel.

This matters because the same county can contain municipalities with separate zoning ordinances, permit procedures or rental rules. Use the Jurisdiction Finder first, then open the county or municipality guide for the property you are evaluating.

2. Verify the existing primary dwelling and property record

Maryland’s statewide ADU framework is built around land with an existing single-family detached dwelling, while some local laws may authorize additional configurations. Do not assume a listing described as “single-family” answers every zoning question.

Use the Maryland Department of Assessments and Taxation Real Property Data Search to review the parcel record, account identifier, land use, primary structure information and other public property data. SDAT says the database can be searched by address or property account identifier and cautions that its information should not be used as a legal report or document.

Then confirm the actual zoning classification with the local planning or zoning authority. The tax record is useful for orientation; it is not a zoning approval.

3. Check the local ADU law that will apply when you build

Maryland’s 2025 ADU law took effect October 1, 2025 and requires local governments to adopt qualifying local ADU laws by October 1, 2026. The Maryland Department of Planning explains that local zoning, application procedures and other local requirements still matter. See the State’s HB 1466 ADU FAQ.

For a property purchase, check both the current rule and any adopted-but-not-yet-codified or pending local measure. Our Maryland ADU Rules Tracker and local jurisdiction guides separate adopted, effective and pending changes.

4. Do not use an online parcel line as your construction boundary

Online parcel maps are useful for initial screening, but the Maryland Department of Planning expressly says its tax maps are not legal descriptions, are not survey products, and should not be used for the design or construction of improvements. See MDP’s Tax Maps guidance.

Before assuming an ADU will fit, look for an existing survey, location drawing or recorded plat. Maryland State Archives’ PLATS.NET provides access to recorded plats filed with Maryland courts and the Land Office. Its guidance explains that plats show property boundaries described in deeds.

The Maryland Courts land-records guidance also notes that ordinary house location surveys are rarely recorded in land records. If an accurate boundary is needed and no suitable survey is available, a licensed land surveyor may be necessary.

For the next step, use our Maryland ADU Site Plan Guide.

5. Draw the real buildable envelope, not the whole backyard

The usable ADU area is usually smaller than the visible open yard. Start with the property boundary, then subtract the constraints that apply to the parcel:

• required side and rear setbacks;
• building restriction lines;
• recorded easements;
• existing buildings and accessory structures;
• septic system and replacement/reserve area;
• well separation areas;
• floodplain or drainage constraints;
• Critical Area or environmental limits;
• lot-coverage or impervious-surface limits;
• required access or utility corridors.

Read the Maryland ADU Setback Guide and Maryland ADU Lot Coverage Guide before treating the apparent backyard dimensions as buildable space.

6. Look for easements before you fall in love with one ADU location

Utility, drainage, access and other easements can cross the exact area where a detached ADU appears easiest to place. A recorded plat or title documents may identify easements that are not obvious during a property showing.

An easement does not automatically mean an ADU is impossible, but it can change placement, design and approval requirements. If an easement affects the proposed footprint, identify who holds the easement and what restrictions apply before relying on that location.

7. For septic properties, investigate capacity before design

On a property with private septic, the limiting factor may be wastewater capacity rather than yard size. Existing system design, bedroom count, repair area and local health-department requirements can affect whether an ADU can be supported.

Do not assume that a large lot means septic approval will be simple. Review our Maryland ADU Septic & Well Guide and request the available septic/well records from the reviewing health authority before committing to a bedroom count or ADU location.

8. For public water and sewer, check connection logistics and fees

A property connected to public utilities avoids some septic constraints, but a detached ADU can still require new service routes, meter decisions, sewer connection work, trenching or utility review.

Distance from the main house, driveway crossings, mature trees, retaining walls and existing utility easements can materially affect cost. Use the Maryland ADU Utilities Guide before assuming the cheapest-looking ADU location will also be the cheapest to serve.

9. Check floodplain, Critical Area and historic constraints

Some Maryland properties need additional review because of mapped overlays or protected resources. These issues are highly property-specific and can affect placement, disturbance limits, exterior changes or review steps.

For waterfront and Chesapeake Bay-area properties, review our Maryland ADU Critical Area Guide. For older properties or designated districts, use the Maryland ADU Historic District Guide. Floodplain status should be confirmed with the reviewing jurisdiction rather than inferred only from a real-estate listing.

10. Check HOA and private restrictions separately from zoning

A zoning approval and a private covenant are different things. Maryland’s ADU law limits unreasonable private restrictions on ADUs, but that does not mean every declaration, architectural-review rule or recorded covenant can be ignored.

If the property is in an HOA or condominium regime, obtain the current declaration, bylaws and architectural guidelines before you buy. Use our Maryland ADU HOA Rules Guide to understand the state-law framework and what still needs property-specific review.

11. Match the property to your actual ADU plan

A property that works for a 450-square-foot interior conversion may not work for a 750-square-foot detached cottage. Before comparing homes, define the project you actually want:

• interior/basement ADU;
• attached addition;
• garage conversion;
• detached backyard unit;
• one-bedroom versus two-bedroom;
• family use versus long-term rental;
• future aging-in-place use;
• prefab/modular versus site-built construction.

If you are considering an existing garage, use the Maryland Garage Conversion ADU Guide. If you are comparing prefab options, read the Maryland ADU Builders & Prefab Guide only after the property constraints are understood.

12. Check rental rules before assuming the ADU will generate income

If rental income is part of the reason you are buying the property, verify the intended rental model before using projected rent in your decision. Local jurisdictions may have rental-license, inspection or owner-occupancy requirements, and short-term rental rules can differ from long-term ADU rental rules.

See the Maryland ADU Rental & Short-Term Rental Guide and the property’s local jurisdiction guide.

Pre-offer Maryland ADU property checklist

Five red flags that deserve a closer look

• The listing says “ADU potential” but gives no zoning source. Treat that as marketing language until the reviewing jurisdiction confirms the property’s rules.
• The only boundary shown is an online parcel map. Maryland says tax maps are not survey products and should not be used for construction design.
• The backyard is large, but the property uses septic. Capacity and reserve-area constraints can matter more than gross lot size.
• The ideal ADU location sits over a visible utility line, drainage area or recorded easement. Verify the rights and restrictions before design.
• Your financial plan depends on short-term rental income. Confirm the local rental rules before using that income assumption.

What to ask before making an offer

For a property that looks promising, send the planning or zoning office a short, specific question rather than asking “Can I build an ADU?” Include the address, proposed ADU type and approximate size, and ask:

• Which zoning authority controls this parcel?
• Is an ADU permitted under the current local law for this property type?
• What side/rear setback and lot-coverage standards should I use for a preliminary concept?
• Are there mapped overlays or special reviews I should check?
• For a detached ADU, what plot plan or survey information will eventually be required?
• If the property is on septic/well, which health authority should review feasibility?
• If I plan to rent the ADU, what separate licensing or occupancy requirements apply?

Howard County illustrates why this matters: its current ADU application requires a plot plan showing compliance with size and setback limits, and newly constructed ADUs must also address water conveyance so neighboring properties and subdivision stormwater facilities are not adversely affected. See Howard County’s official ADU application page. Requirements differ elsewhere, so use that as an example of the level of parcel-specific review that can appear—not as a statewide checklist.

A good next step after the property passes this screen

If the property survives the checks above, move from “possible” to a measured concept: confirm the jurisdiction, obtain the best available survey/plat, sketch the buildable envelope, identify septic/utilities and overlays, and then test the concept in the Maryland ADU Property Feasibility Checker.

Only after those constraints are understood does it make sense to compare floor plans, prefab models, architects or builders.

Official sources used

• Maryland Department of Planning — ADU FAQ for Local Governments (HB 1466)
• Maryland SDAT — Real Property Data Search
• Maryland Department of Planning — Tax Maps
• Maryland State Archives — PLATS.NET
• Maryland Courts — Land Records FAQ
• Howard County — Accessory Dwelling Unit Application