Existing space, new dwelling questions
A walk-out basement may offer a useful starting point for an ADU, but an exterior door and finished walls do not establish approval for a separate dwelling. Before drawing a kitchen or ordering windows, check the local ADU route, finished ceiling heights, escape openings and the separation from the main home.
This is a preparation guide. Confirm the adopted code, amendments and existing-building provisions with the office reviewing your property. The dimensions below are an Anne Arundel example, not a statewide determination.
1. Confirm that the proposed use has an ADU approval path
Begin with the Jurisdiction Finder and the relevant local guide. Describe the actual proposal: separate living facilities, sleeping rooms, cooking facilities and how it connects to the main dwelling. Ask which zoning, building and licensing approvals apply.
Gather the existing permit records. A previously finished basement is not proof that a separate dwelling was approved. Ask how the reviewing office treats the proposed conversion under its current code and any provisions for existing buildings.
2. Measure the finished height, including low points
Prepare a room-by-room sketch with measurements beneath beams, ducts and soffits, plus the stair headroom. Record the existing floor and ceiling finishes and the proposed changes. A new floor build-up or ceiling assembly can reduce the usable height.
Anne Arundel example: its residential code summary lists 7 feet for habitable rooms, 6 feet 8 inches for other areas, and 6 feet 4 inches beneath beams and ducts. The county labels this a general guide. Ask which category and any exceptions apply to each part of your conversion; do not treat the lowest listed height as permission for the entire room.
Budget question: can the layout and services fit within the permitted height, or would structural work be needed? Have a qualified designer evaluate that before assuming a basement conversion will be inexpensive.
3. Check each sleeping room, not just the walk-out door
Show every proposed bedroom, door, window and route outside on the plan. Ask the reviewer to distinguish the required exit route from emergency escape and rescue openings. An exterior basement door does not, by itself, establish compliance for every sleeping room.
Anne Arundel example: the county’s construction inspection sheet describes basement and sleeping-room escape openings with a 5.7-square-foot net clear area, a 5.0-square-foot provision for grade-floor windows, minimum clear height of 24 inches, minimum clear width of 20 inches and maximum sill height of 44 inches. It also points to exceptions, including provisions for sprinklered dwellings. The reviewing office must determine which provisions apply.
Measurement trap: a clear opening 20 inches wide and 24 inches high is only 3.33 square feet. Meeting the separate minimum width and height does not necessarily meet the area requirement. Measure the unobstructed opening with the window open, rather than its frame or glass size.
For an opening below grade, include the well, access and drainage in the review. Ask a designer to assess any proposed enlargement through a foundation wall before pricing or cutting it.
4. Review separation, moisture and services together
Ask for a drawing showing how the proposed ADU is separated from the home, including floors, walls, doors and service penetrations. Request the required assembly details for this layout; a garage separation detail is not automatically a basement dwelling-separation detail.
Document evidence of water entry and discuss drainage, moisture control and ventilation with the designer. Also identify heating, electrical, plumbing and alarm work. These are questions to resolve in the design scope, not a claim that every conversion needs the same upgrade.
On septic, check the approved system records and proposed sleeping capacity even if the building footprint stays unchanged. Use the Septic & Well Guide to prepare those questions.
5. Bring a focused brief to the designer
- Confirmed reviewing office and the intended ADU use.
- Existing approvals and a measured layout.
- Finished-height measurements at rooms, beams, ducts and stairs.
- Proposed sleeping rooms, escape openings and exterior access.
- Known moisture, utility and structural questions.
- A budget with unresolved work marked as allowances or exclusions.
Next: prepare your design-team brief →
Once the scope is defined, follow the permit-to-completion guide for application, inspection and handover planning. You can also return to My ADU Plan.
Source review: September 14, 2026. Local examples illustrate what to check; they do not replace property-specific review.
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.