ADU Types
Which Type of ADU Is Right for Your Property?
There are five practical ways to add an accessory dwelling unit to a Maryland home. The right one depends less on preference than on what your lot and your existing house already give you to work with.
Two questions decide most of this. First, do you have usable space already — an attached garage, a full-height attic, a basement with or without a walk-out? Converting existing space is almost always faster and cheaper than building new. Second, how separate does the unit need to be? A detached unit in the backyard gives a tenant or family member genuine independence; an in-law suite attached to the house keeps everyone under one roof.
The Five ADU Types We Build
Detached ADU
$150,000 – $300,000+
A standalone structure in the backyard with its own foundation, utilities, and entrance. The most flexible option and the most private for whoever lives there, which is why it commands the strongest rent. It is also the biggest build: foundation, utility runs, full exterior envelope. Best suited to lots with real backyard depth and room to meet setbacks.
Garage Conversion ADU
$90,000 – $150,000
Turning an attached or detached garage into a living unit. Usually the fastest route to a finished ADU because the structure and slab already exist — the work is insulation, egress, plumbing, electrical, and finishes. The trade-off is losing covered parking, which matters more on some streets than others.
Basement Conversion ADU
$80,000 – $140,000
Often the lightest lift of any ADU type, especially where there is already a walk-out or a window well that can be brought up to egress. Ceiling height, moisture control, and a compliant second exit are the three things that decide whether a basement works. Many Anne Arundel County homes are good candidates without realizing it.
Attic Conversion ADU
$100,000 – $160,000
Using upper-floor square footage you already pay taxes on. Viability comes down to headroom, floor framing that can carry living loads, insulation, and a compliant stair and egress. Where it works it is an elegant answer, because it adds a unit without touching the yard or the footprint.
In-Law Suite Addition
$120,000 – $220,000
An attached addition built for multigenerational living — private bedroom, bathroom, living space, and usually a kitchenette, with its own entrance. The usual choice when the point is to keep a parent close rather than to rent. Built to the same code standard as the main house and designed to read as part of it, not bolted on.
How to Narrow It Down
- Want maximum rent and have the yard for it — detached ADU.
- Want the lowest cost and have a garage you can give up — garage conversion.
- Have a walk-out basement — basement conversion, usually the cheapest path of all.
- Have real attic headroom and no yard to spare — attic conversion.
- Housing a parent rather than a tenant — in-law suite.
If you are not sure which of these your property supports, that is exactly what the free consultation is for. We walk the lot, look at the existing structure, and tell you what is actually feasible before anyone spends money on drawings.
Cost and Permitting by Type
The ranges above are starting points. What moves them is site prep, utility runs, foundation type, finish level, and permitting — our Maryland ADU cost guide breaks down how hard and soft costs divide and what pushes a quote in either direction.
Every type here requires a permit in Anne Arundel County under Bill 6-23, and Maryland’s statewide ADU Act sets the by-right baseline. Our guide to Maryland ADU law covers what each requires. We handle the permitting either way.
Not Sure Which Type Fits Your Lot?
We build all five across Annapolis, Glen Burnie, Pasadena, Severna Park, Crofton, and Odenton. Call (410) 755-7663 or request a free on-site consultation and we will tell you which options your property actually supports.