The sequence (order matters)
Permits go in a fixed order in Charles County. Do them out of order and you redo work.
First — the lot check. Make sure your zoning district allows an ADU and that the size, setback, and bedroom caps fit what you want to build. Our free feasibility study does this on your actual property, with measurements.
Second — the health department. Before any ADU or building permit can be issued, the health department has to sign off on your water supply and sewage disposal (the county's published draft rules require this up front). On septic, this step decides the project: bedroom additions count as new system load, so bring your existing septic records to this appointment. Division of Environmental Health: 301-609-6751.
Third — the ADU Unit Permit. This is the ADU-specific approval from the zoning administrator, and it comes before the building permit and before any excavation. No ADU Unit Permit, no digging.
Fourth — building and trade permits. The standard building permit plus the trade permits for electrical, plumbing, and HVAC.
Fifth — inspections to the finish line. The county inspects at stages through completion. If the project runs long, the permit can be extended up to 180 days for $63.
Sources: Charles County Bill 2026-06 / ZTA 25-189 (published draft, §§3.01.700.D, J); new Art. XXVI §297-430.E.
Paperwork to gather before you apply
Having these ready keeps the application "complete" — and completeness is what the 90-day state clock runs on: a site plan or survey showing lot lines, the main house, and the proposed ADU location with setbacks marked; your septic records (or water/sewer account info if on public systems); floor plans and elevations drawn to scale; HOA architectural approval in writing, if your neighborhood has an HOA; and the health-department sign-off from step two. Missing items are the #1 reason applications stall.
Mistakes that restart the clock
Applying for the building permit first. The ADU Unit Permit comes first — a building permit application without it goes nowhere.
Skipping the health department. No water/sewer approval, no permits at all. This is the gate most first-timers miss.
Paying for full architectural plans before feasibility. If the lot cannot carry the ADU (setbacks, septic), expensive plans are scrap paper. Feasibility first, drawings second.
Assuming the HOA is handled. County approval and HOA approval are separate gates — the county's staff position is "HOA guidelines apply."
The real fee schedule (FY2027)
Charles County publishes its fees, effective July 1, 2026. For an ADU:
Building permit application: $120
Residential plan review: $0.19 per square foot ($139 minimum) — about $190 on a 1,000-square-foot ADU. Covers up to 3 reviews; a 4th review bills at $222/hour.
Trade permits: $28 each
Inspections: $94–$328 each
Reviews: Tier 2 engineering $75, environmental $23, zoning $23
Home Builder's Guaranty Fund: $50
Two things the schedule does not answer: the Fair Share Excise Tax rate and whether ADUs are exempt (unverified), and review timelines (the county publishes none).
Sources: Charles County FY2027 Fees & Charges (charlescountymd.gov).
State-law protections on your side
Maryland law requires the county to decide complete ADU applications within 90 days, with no discretionary hearing. "Complete" is doing heavy work in that sentence — an application missing the health-department sign-off is not complete. And: no impact fees or excise taxes on ADUs under 750 square feet; above that, fees must be proportional to the main home's size.
Sources: Chapter 197 of the 2025 Laws of Maryland (HB 1466/SB 891), §§4-505, 4-506.
A note on prices: fees change when the county updates its schedule — confirm current figures at permit time. Your written estimate after our free lot walk reflects the fees in effect then.
Check it yourself
Fee schedule: charlescountymd.gov (FY2027 Fees & Charges). Zoning questions: Planning & Growth Management, 301-645-0692. Or skip the homework: call (240) 222-5082 — permits are our paperwork, not your headache.