Maryland ADU architect screening guide
Hire the designer after you understand the property.
Before you pay for plans, verify the five decisions that can force a Maryland ADU redesign: zoning authority, current rule set, size method, site constraints and permit scope.
This is not an architect directory. It is a mistake-prevention screen.
The question is not whether a designer can draw an attractive ADU. The question is whether the team has a repeatable process for verifying the rules and site assumptions that control those drawings. Use the questions below before a full permit set is commissioned.
Start with jurisdiction and zoning
Which government controls zoning?
Why it mattersCounty names alone do not always identify the final zoning authority.
Ask forThe parcel’s actual planning/zoning authority and the source used to verify it.
Which ADU rule set is in force today?
Why it mattersMaryland’s October 1, 2026 local-law adoption deadline has passed. Confirm the currently effective local rule and any unresolved implementation questions.
Ask forThe ordinance, bill or zoning section being used—and the date it was checked. Cross-check our tracker →
How will the maximum ADU size be calculated?
Why it mattersMaryland does not prescribe one universal measurement method for the 75% rule.
Ask forThe exact measurement method used locally. Maryland Planning recommends finished living area above grade; Howard County’s published guidance uses exterior footprint. Verify the applicable local basis rather than substituting one measurement for another. Use the 75% calculator →
Which setbacks, height and lot limits apply?
Why it mattersThe statewide setback guardrail does not create one Maryland setback number.
Ask forThe parcel’s zone, accessory-structure standards, easements, lot coverage and height limits.
Then test the site and approval path
What approval path applies?
Why it mattersMaryland allows local by-right, conditional-use and special-exception approaches.
Ask forThe path for this parcel and any extra review triggered by the concept.
What parking rule applies?
Why it mattersExtra ADU parking is constrained by HB 1466’s study and waiver requirements.
Ask forThe current local parking rule and whether a waiver process matters to the design.
What utility, well or septic issue comes first?
Why it mattersPublic-health and infrastructure constraints can change a layout before architecture begins.
Ask forWho verifies wastewater capacity, reserve area, well issues and utility routing. Open the readiness guide →
Is an existing garage or accessory structure legally usable?
Why it mattersA conversion is not automatically simpler just because the shell already exists.
Ask forPermit history, structural condition, setbacks, access, utilities and code implications.
Finally, protect the contract and permit scope
What site conditions could move or shrink the footprint?
Why it mattersA theoretical size ceiling is not the same as a buildable envelope.
Ask forEasements, stormwater, drainage, slopes, trees, access and utility corridors.
What assumptions are you making?
Why it mattersUnwritten assumptions become expensive when an agency reviewer changes the premise.
Ask forA written assumptions list and the cost treatment if one changes.
Can the work be staged?
Why it mattersUnresolved feasibility questions do not always justify a full construction set on day one.
Ask forSeparate feasibility, schematic-design and permit-drawing milestones.
Who owns permit coordination and resubmittals?
Why it mattersDrawing plans and managing agency review are different services.
Ask forWho submits, who answers comments, how many revision rounds are included and which consultants are extra.
Why “Maryland experience” is not specific enough
Two jurisdictions can sit under the same statewide law and still require different measurements or implementation checks.
Verified example
Howard County
Current county guidance uses 75% of the exterior footprint of the principal dwelling. A designer using total interior living area could start from the wrong ceiling.
2026 transition example
Montgomery County
The existing detached-ADU framework historically used a different local formula while ZTA 26-06 moves toward HB 1466 alignment. The operative rule should be rechecked when plans are prepared.
Contract screen
Before you pay a design deposit
- Zoning authority identified
- Current ADU rule dated
- Size method documented
- Setbacks and lot limits checked
- Approval path identified
- Parking rule checked
- Utilities or septic confirmed
- Site constraints assigned
- Assumptions written down
- Resubmittal responsibility defined
Use this page as the meeting worksheet
Print it or save it as a PDF and mark the 12 answers during the interview.
Walk-away signals
Red flags
- They give you a size from memory without naming the measurement method
- They assume the county answer is enough without checking zoning authority
- They quote “standard Maryland setbacks” without identifying the parcel’s zone
- They promise a permit date before confirming the approval path
- They defer septic, drainage or utility questions until after layout design
- The agreement is silent about agency-driven redesign or resubmittals
Best next step
Screen the property before you screen designers.
Build a clearer property brief first. Then take the flagged questions into the first architect or design-build meeting.
Primary sources
- Maryland Department of Planning — HB 1466 ADU FAQ
- Maryland Department of Planning — Model Local ADU Ordinance
- Howard County — Accessory Dwelling Units
- Montgomery County Council — Zoning Text Amendments
Last reviewed: September 7, 2026. Planning and consumer-screening information only; not legal, architectural, engineering, zoning or permitting advice.
What to do next
Start by finding the office that reviews your property. A mailing city or a county guide does not establish your parcel’s authority.
- Find Who Reviews My Property.
- Obtain your parcel identifier, survey, floor plans and utility records.
- Ask the reviewing office which current rules, supporting documents and approvals apply.
- Continue to your planning workspace.
Enable JavaScript to prepare a downloadable next-step brief. Planning guidance is not permit approval.