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FAQs · Waldorf, MD

Every ADU Question, Answered Honestly

The questions Charles County homeowners actually ask — about cost, legality, timelines, renting, and HOAs — answered straight, with sources you can check.

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

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How much does an ADU cost?

There is no single price for an ADU. Size, type, and your lot all move the number. But published figures from real builders show the range. Makara ADU, a Maryland builder, was quoted in The Banner saying an ADU costs $150K–$350K to build, with about 3–4 months of construction. Excell Homes publishes $150K–$200K for a turnkey 600-square-foot detached unit. Foster Remodeling publishes $50K–$200K for conversion-type projects in Northern Virginia. Powell Custom Homes gives an industry-wide figure of $150–$300 per square foot.

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.

Want the full picture of what an ADU can earn back? See our rental-income ADU page.

Sources: Makara ADU (quoted in The Banner); Excell Homes (excellhomes.us/adu, published figures); Foster Remodeling (fosterremodeling.com, published figures); Powell Custom Homes (industry-wide figure).

Are ADUs legal in Maryland?

Yes. Maryland's ADU law — Chapter 197 of the 2025 Laws of Maryland (HB 1466/SB 891) — has allowed ADUs by right since October 1, 2025. "By right" means the county must judge your application against clear, written rules. For complete applications, the county must approve or deny within 90 days, in a plain review with no discretionary hearing. Homeowners across our service area are covered by the same state law.

Sources: Chapter 197 of the 2025 Laws of Maryland (HB 1466/SB 891), §§4-504(A)(1), 4-505.

How long does an ADU take?

The honest answer: it depends on your lot, your ADU type, and the county's permit queue. Maryland law requires a decision on complete applications within 90 days — but the county publishes no review timeline of its own, and "complete" is the key word. Our ADU timeline guide walks through design, permits, and construction with published builder numbers — and names exactly where the uncertainty lives.

Sources: Chapter 197 of the 2025 Laws of Maryland (HB 1466/SB 891), §4-505; Charles County permit review timelines UNVERIFIED.

Can I rent out my ADU?

For a long-term tenant — a 12-month lease, for example — nothing in Maryland's ADU law or Charles County's published draft rules bans renting your ADU. The big exception is short-term rentals: your HOA can ban Airbnb-style use, and some do. Check your HOA's rulebook before you count on short-term rental income.

For the full math on renting, see our rental-income ADU page.

Sources: Chapter 197 of the 2025 Laws of Maryland (HB 1466/SB 891); Real Property §2-126 (HOAs may restrict short-term rental); Charles County Bill 2026-06 / ZTA 25-189 (published draft).

Can I build an ADU on septic?

Maybe — and the health department decides, not the zoning code. Under Charles County's published draft rules, the health department must approve your water supply and sewage disposal before any ADU or building permit is issued. Adding a bedroom counts as new load on the septic system, and the county has not published specific sizing numbers for ADU bedrooms. Our ADUs on septic guide explains the approval order and what to check first.

Sources: Charles County Bill 2026-06 / ZTA 25-189 (published draft, §§3.01.700.D, J); Health Department BRF guidance (adding bedrooms = new construction).

Your HOA gets a vote too

Maryland law says your HOA can't unreasonably limit your ADU — nothing that drives the cost way up or blocks the project in practice. But the HOA still has teeth: it can ban short-term rentals of the ADU, and it can treat the ADU as a separate lot for dues and voting. The county's own staff position is "HOA guidelines apply" — the county won't overrule your neighborhood's private covenants. Read your CC&Rs before you pay for plans, and get the HOA's architectural approval in writing early. Sources: Real Property §2-126 (Chapter 197 of the 2025 Laws of Maryland); Charles County staff briefing to the Board of County Commissioners, April 28, 2026.

Check it yourself — or skip the homework

Don't take our word for any of this. 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. The county's published draft rules are Bill 2026-06 / ZTA 25-189 ("Flexibility for Accessory Dwelling Units"); the state law is Chapter 197 of the 2025 Laws of Maryland (HB 1466/SB 891).

Or skip the homework: call (240) 222-5082 and we'll walk your lot free and tell you what your county allows — before you spend a dollar.

Questions homeowners ask us

Are ADUs legal in Maryland?

Yes — Maryland's ADU law (Chapter 197 of the 2025 Laws of Maryland, HB 1466/SB 891) has allowed them by right since October 1, 2025. That means the county judges your application against clear written rules and must decide complete applications within 90 days, with no discretionary hearing. Charles County's own implementing rules (Bill 2026-06) are published as a draft; final adoption is being confirmed.

How much does an ADU cost?

Published builder figures give the range: Makara ADU quotes $150K–$350K (per The Banner); Excell Homes publishes $150K–$200K for a turnkey 600 sq ft detached unit; Foster Remodeling publishes $50K–$200K for conversion-type projects in Northern Virginia; Powell Custom Homes gives $150–$300 per square foot industry-wide. 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.

How long does it take?

There is no promised timeline. Maryland law requires a decision on complete applications within 90 days — but Charles County publishes no review timeline of its own, and an incomplete application does not start the clock. Our ADU timeline guide breaks down each phase with published builder numbers.

Can I rent out my ADU?

Long-term rental is generally allowed — nothing in the state ADU law or the county's published draft rules bans it. Short-term rentals are the exception: your HOA can ban Airbnb-style use. Check your CC&Rs before you plan on it.

What if my HOA says no?

An HOA cannot unreasonably block your ADU under Maryland law — anything that drives the cost way up or blocks the project in practice is off limits. But the HOA can still ban short-term rentals and treat the ADU as a separate lot for dues and voting. And the county staff position is "HOA guidelines apply" — the county will not overrule your private covenants. Read your CC&Rs before you pay for plans.

Do I need a big lot?

Not necessarily. Maryland sets no minimum lot size, and Charles County's draft rules allow ADUs on lots of any size. On lots under 3 acres, the ADU is capped at 1,000 square feet or 75% of your main house's floor area, whichever is smaller; on 3+ acres, the cap is 75% with no absolute limit. One ADU per lot, maximum 2 bedrooms. These are published draft rules — final adoption is being confirmed. On septic, the health department's limits may matter more than the lot size.

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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