The sequence — order matters
1. Health-department water/sewer approval FIRST
Before any building permit or ADU permit, the health department must approve your water supply and sewage disposal. This is the gate that kills the most projects — especially on septic, where added bedrooms count as new construction for the county's sizing math. We start here, not at the permit counter.
Sources: Charles County Bill 2026-06 / ZTA 25-189 (published draft), §§3.01.700.D, J; due-diligence report (Charles County septic sizing numbers unverified — ask the Health Department, 301-609-6751).
2. The Accessory Dwelling Unit Permit
Next comes a dedicated Accessory Dwelling Unit Permit from the zoning administrator — required before any building permit is issued and before any excavation begins. Clear your lot early and you've violated the sequence, so we don't. If the permit stalls, extensions of up to 180 days are available for $63.
Sources: Charles County Bill 2026-06 / ZTA 25-189 (published draft), new Art. XXVI §297-430.E; extension fee $63 per county fee schedule.
3. Building + trade permits
Then the building permit itself, plus trade permits at $28 each — electrical, plumbing, mechanical, and any others your project needs. The county's fee schedule covers up to 3 plan reviews; a 4th or later review is billed at $222/hour, which is why we file complete applications the first time.
Sources: Charles County FY2027 Fees & Charges (effective 7/1/2026): trade permits $28 each; plan review $0.19/sq ft ($139 minimum); up to 3 reviews included, 4th+ at $222/hr.
4. Inspections at required stages
The county inspects the work at its required stages — foundation, framing, rough-ins, final. Inspection fees run $94–$328 depending on the inspection. We schedule them, meet the inspectors, and handle any corrections.
Sources: Charles County FY2027 Fees & Charges (effective 7/1/2026): inspections $94–$328.
The fees, line by line
Here are the county's published fees for a residential building permit application — every one of them from the FY2027 Fees & Charges schedule, effective July 1, 2026:
- Application: $120
- Plan review: $0.19 per sq ft ($139 minimum) — a 1,000-sq-ft detached ADU is about $190
- Trade permits: $28 each
- Tier 2 engineering review: $75
- Environmental review: $23
- Zoning review: $23
- Home Builder's Guaranty Fund: $50
- Inspections: $94–$328 each
A rough starting-point example: a 1,000-sq-ft detached ADU ≈ $190 plan review + $120 application + trade permits + inspections. One fee we won't quote: the Fair Share Excise Tax rate and whether it applies to ADUs at all — the county hasn't published that, so we'll check it for your address rather than guess.
Sources: Charles County FY2027 Fees & Charges (effective 7/1/2026); 1,000-sq-ft example is arithmetic from the published rates; Fair Share Excise Tax unverified — per due-diligence report.
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.
The 90-day rule — and what it doesn't say
Maryland state law says the county must approve or deny a complete ADU zoning-use application within 90 days, decided ministerially — meaning no discretionary public hearing on the decision. That's real protection against a permit dying in a meeting. But it only covers complete applications, and the county's typical review time in practice is not published. Both things are true at once: the law caps the clock, and we still won't promise you a date.
Sources: §4-505 (Chapter 197 of the 2025 Laws of Maryland (HB 1466/SB 891)); county typical review timelines unverified — per due-diligence report.
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. Already know your lot works? See what construction looks like, or start over at step one.