Garage Conversion ADU Cost in Maryland

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Thinking about converting your garage? Get a free walk-through — we will tell you if the bones are worth it.

Bright finished garage conversion apartment interior

The short answer

Foster Remodeling publishes $50,000–$200,000 for conversion-type ADU projects in Northern Virginia — their published range, not our quote. Conversions cost less than new detached builds because the big-ticket items already exist: foundation, framing, and roof. You are finishing a structure, not raising one.

A note on prices: material costs move up and down, and no two lots need the same work. Treat any numbers on this page as starting points, not quotes. Your written estimate after our free lot walk is the real number for your project.

Sources: Foster Remodeling (fosterremodeling.com, published figures).

What your garage needs to qualify

Not every garage converts well. The good candidates share four traits: solid bones (foundation and framing in decent shape), ceiling height (low ceilings mean expensive reframing or a raised roof), plumbing proximity (a bath and kitchen need water and drain lines — the farther from the house's existing plumbing, the pricier the run), and electrical capacity (an older 100-amp panel serving the whole house may need an upgrade to carry a second dwelling).

See the full picture on our garage conversion ADU page — what the project involves step by step.

Where the money goes

The big-ticket items in a conversion: insulation and climate (most garages were never built to be lived in — walls, slab edge, and often the roof need insulating), plumbing (cutting slab for drain lines is the single most variable cost), electrical (panel, circuits, and lighting for a full dwelling), windows and entry (egress windows are a code requirement for sleeping rooms), and finishes (flooring, kitchen, bath — the same choices that move any remodel's price).

On permits: Charles County's published draft rules require health-department approval of water and septic before any ADU or building permit — that applies to conversions too, not just new builds. And the county's FY2027 fee schedule still applies: $120 application, plan review, trade permits.

Sources: Charles County Bill 2026-06 / ZTA 25-189 (published draft, §3.01.700.D); Charles County FY2027 Fees & Charges (charlescountymd.gov).

When new construction wins

Run the honest comparison when: the garage foundation is failing, the ceiling is too low to fix cheaply, the plumbing run crosses the entire house, or the electrical panel needs a full upgrade anyway. At that point you are paying new-construction prices for a compromised result — a small detached cottage or small ADU may deliver more home for similar money. Our detached vs. conversion comparison lays the two paths side by side.

We will tell you which camp your garage falls in on the free walk-through — including when the answer is "don't convert it."

Check it yourself — or skip the homework

Zoning and permit questions: Charles County Planning & Growth Management, 301-645-0692. Well and septic questions: Health Department, Division of Environmental Health, 301-609-6751.

Or skip the homework: call (240) 222-5082 — we will look at your garage and give you a straight answer.

Questions homeowners ask us

Is converting my garage cheaper than building a detached ADU?

Usually, yes — the foundation, framing, and roof already exist. Foster Remodeling publishes $50,000 to $200,000 for conversion-type projects, well under detached new-build ranges. But a garage with bad bones (failing foundation, low ceilings, distant plumbing) can close the gap fast. Price both paths before you decide.

Do I lose my parking if I convert the garage?

The garage stops being a garage, yes. The good news on rules: Charles County's published draft amends the parking table to require no off-street parking spaces for ADUs, and Maryland law caps what any county can require. Check your HOA, though — some require covered parking regardless of what the county says.

Can I convert a detached garage?

Yes — detached garages convert well, and they make great ADUs because the separation gives privacy. The same four checks apply: bones, ceiling height, plumbing distance, and electrical capacity.

How long does a garage conversion take?

Faster than new construction — there is no foundation or framing phase. The permit path is the same as any ADU: health-department sign-off first where it applies, then the county's ADU permit, then the building permit. Maryland law requires a decision on complete applications within 90 days; the county publishes no review timeline of its own.

What is the biggest surprise cost in garage conversions?

Plumbing. Cutting a concrete slab to run drain lines to a new bath and kitchen is the most variable cost in the project — a short run to nearby existing plumbing is cheap, a long run across the house is not. That is the first thing we check on a walk-through.

What happens after you reach out

No mystery, no sales script. Here is the whole path from first call to move-in day.

1You reach outCall or send the form. Tell us about your lot and what you want the space for — a parent, rental income, a home office.

2We walk your propertyFree visit. We check setbacks, access, slope, trees, and utilities, and tell you honestly what fits.

3You get a plan and a priceA site plan and a written estimate for your lot. No pressure, no obligation, no fine print.

4Permits, then buildWe handle the Charles County paperwork and follow-ups. Then our partner builders build it.

What a Garage-to-ADU Conversion Costs