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ADU Cost Guide · Head-to-Head

New Detached Build or Garage Conversion?

The two most popular ADU paths, compared on cost, timeline, and what you give up with each. Published builder figures on both sides.

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Free on-site estimates  ·  No-pressure advice  ·  Waldorf and Charles County, MD

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Garage or backyard? We will walk both and price both — then you decide with real numbers.

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Free on-site estimatesWe walk your lot before we ever talk price.
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Plans drawn for your lotEvery ADU starts with a site plan, not a template.
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Permit paperwork handledCharles County forms, filings, and follow-ups.
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15+ years of remodeling experienceA decade and a half of home remodeling know-how on your side.
Framing crew raising the custom walls of a backyard cottage ADU

Cost: the published figures

Detached new build: Makara ADU publishes $150,000–$350,000 to build an ADU (quoted in The Banner); Excell Homes publishes $150,000–$200,000 for a turnkey 600-square-foot detached unit. Everything is new — foundation, framing, roof, systems.
Garage conversion: Foster Remodeling publishes $50,000–$200,000 for conversion-type projects in Northern Virginia. The structure exists, so you pay for transformation, not construction from dirt.

The gap narrows when the garage fights back: failing foundation, low ceilings, distant plumbing, or a maxed-out electrical panel. Price both paths on your actual garage before you commit — that is what the free feasibility study is for.

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: Makara ADU (quoted in The Banner); Excell Homes (excellhomes.us/adu, published figures); Foster Remodeling (fosterremodeling.com, published figures).

Timeline: what the builders publish

Makara ADU cites about 3–4 months of construction (quoted in The Banner) — that is build time, not including design and permits. Excell Homes publishes 5–7 months from start to move-in: roughly 2–3 weeks of design, 30–60 days of permits, and 12–16 weeks of construction. Those are the builders' published figures for their projects, not promises for yours.

Conversions skip foundation and framing, so construction runs shorter — but the permit path is the same: health-department sign-off first where it applies, then the county ADU permit, then the building permit. Maryland law requires a decision on complete applications within 90 days; Charles County publishes no review timeline of its own.

Sources: Makara ADU (quoted in The Banner); Excell Homes (excellhomes.us/adu, published figures); Chapter 197 of the 2025 Laws of Maryland (HB 1466/SB 891), §4-505.

What you give up with each

Conversion gives up: parking (the garage is gone), design freedom (you inherit the box), ceiling height, and sometimes light. It also inherits every flaw the garage already had.
Detached gives up: money and yard. It costs more, takes longer, and consumes backyard — plus the full zoning treatment: setbacks (6 feet to side and rear lines on smaller Charles County lots, per the published draft), height caps, and utility trenching.

Sources: Charles County Bill 2026-06 / ZTA 25-189 (published draft, §§3.01.700.E, H).

The decision in one question

Is your garage worth converting? Solid bones, decent ceiling height, plumbing nearby, panel with room — convert it and bank the savings. Anything less — price the detached build honestly, because a compromised conversion at new-construction prices is the worst of both. We will give you both numbers on the lot walk; the land decides.

Deeper dives: garage conversion cost, backyard cottages, small ADUs.

Questions homeowners ask us

How much cheaper is a garage conversion than a detached ADU?

Published figures suggest roughly half to a third: Foster Remodeling publishes $50,000 to $200,000 for conversions, while Makara publishes $150,000 to $350,000 for detached new builds. The gap shrinks if your garage needs major structural, plumbing, or electrical work — price your actual garage, not the average one.

Which is faster: conversion or new detached build?

Conversions are faster in construction — no foundation or framing phase. But permits take the same path either way. Excell Homes publishes 5 to 7 months start to move-in for detached; expect a conversion to trim the construction portion, not the permit portion.

Do I need the same permits for a conversion?

Yes. A garage conversion is still an ADU: health-department sign-off first where it applies, then the county ADU permit, then the building permit. There is no shortcut permit for conversions.

Will a converted garage rent for less than a detached ADU?

Usually a little less — tenants pay for light, ceiling height, and the feel of a real home, where detached units have the edge. But a well-done conversion in a good location still rents strongly. The income gap rarely erases the cost gap.

My garage is detached from the house. Does that change anything?

In your favor, mostly. A detached garage conversion gets the privacy advantage of a detached ADU at conversion prices — separate building, own entrance, no shared walls. Check setbacks for the existing structure and confirm the conversion meets ADU standards.

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.

Not sure what fits your lot? Ask us.

One call settles it — we will tell you what your property can hold and what it would take.

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Serving Waldorf and Charles County, MD

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Every town below gets the same free lot walk and written estimate.

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