ADU rules in Charles County
Charles County passed its ADU bill in the summer of 2026. Bill 2026-06, filed as ZTA 25-189 and titled Flexibility for Accessory Dwelling Units, passed unanimously after the July 7, 2026 hearing. A homeowner in Waldorf, La Plata, Bryans Road or Hughesville can add a second, smaller home on the lot in any zone that allows a single family detached house.
This page is the short version of the rule, the permits you will meet in the order you meet them, and what the published numbers say an ADU costs. When you are ready, the form at the bottom gets you a licensed Maryland builder who already works in Charles County. We do not build the units. We make the match.
Bill 2026-06 (ZTA 25-189)
Passed after the July 7, 2026 hearing
Bill 2026-06, Zoning Text Amendment 25-189, "Flexibility for Accessory Dwelling Units", passed unanimously after the public hearing on July 7, 2026.
It allows one accessory dwelling unit per lot in any zone that allows single family detached dwellings, at up to 75 percent of the primary dwelling, with two bedrooms.
The county cannot weaken the state sprinkler rule, and we found no county ADU sprinkler page, so the building code answers the sprinkler question.
Read on the Charles County news release for Bill 2026-06, October 31, 2026.
What Charles allows
- Where: any zone that allows single family detached dwellings.
- One ADU per lot.
- Size: up to 75 percent of the primary dwelling, the same ceiling the state law sets (Chapter 196 of 2025).
- Bedrooms: two at most.
Detached, attached or basement
Detached
A backyard cottage is a new one family dwelling under the Maryland building code and gets a full NFPA 13D sprinkler system. Outside the Waldorf and La Plata water and sewer areas most lots are on well and septic, which adds the Health Department review and a sprinkler tank and pump.
Attached
An addition with its own entrance and kitchen. Inside a house with no sprinklers the state code treats it as an addition and does not force sprinklers, unless the house is already sprinklered.
Basement
A unit carved out of existing space. Ceiling height, a second way out and moisture decide it. No sprinklers unless the house already has them.
Permits in Charles, in the order you meet them
- 1
Zoning
Zoning review under Bill 2026-06 through Planning and Growth Management: the zone, one per lot, the 75 percent cap and the two bedroom limit.
- 2
Building permit
A residential building permit through Codes, Permits and Inspection Services in La Plata. A detached unit files as new residential construction; a conversion or addition files as an addition or alteration.
- 3
Fire protection permit
A detached ADU gets a 13D sprinkler design and its own sprinkler permit. An attached or basement unit in an unsprinklered house normally does not.
- 4
Health (well and septic lots)
Well and septic lots, most of the county outside the Waldorf and La Plata sewer service areas, need the Health Department to confirm the well and septic carry a second kitchen and bath before the building permit issues.
- 5
Utilities
Public water and sewer in the service areas: a tap off the house line or a new service sized for sprinkler flow on a detached unit. Well lots: a storage tank and booster pump at the unit. Electric is a sub panel or a second SMECO meter.
The whole list, statewide, in the order a homeowner meets it:
ADU permit checklistWhat an ADU costs in Charles County
No builder and no county page publishes a Charles County specific ADU price. The ranges below are Maryland wide, from one named builder page. A well and septic lot pushes the detached number up with the tank, pump and health review.
| Type | Published range |
|---|---|
| Detached new build | $120,000 to $300,000 and up |
| Attached addition | $100,000 to $250,000 |
| Basement conversion | $80,000 to $200,000 |
| Garage conversion | $75,000 to $150,000 |
Source for the table:
Clarksville Construction Services, "How much does it cost to build an ADU in Maryland"County fees
County permit fees come from the Planning and Growth Management fees and charges schedule, adopted each fiscal year. We did not quote dollar lines from it here:
- Building and trade permit application fees are a section of the adopted Planning and Growth Management fees and charges, posted on the county site each July.
- Trade permits (electrical, plumbing, mechanical) and inspections carry their own lines.
- Ask the builder to pull the current fiscal year line for your permit type before you budget.
Source for the fees:
Charles County Planning and Growth Management (fees and charges)Sprinkler cost
A detached unit adds the NFPA 13D sprinkler system. On public water that runs about $1.35 to $1.60 per sprinklered square foot (Maryland Fire Sprinklers cost guide, marylandfiresprinklers.com/cost/). A well lot adds a storage tank and pump, priced on the same guide.
Statewide ranges and how the types compare:
ADU cost in MarylandThe sprinkler question, answered once
Every detached ADU in Charles County gets an NFPA 13D sprinkler system. The county cannot waive it (Public Safety Article 12-504) and Bill 2026-06 is a zoning amendment, so the building code still decides. On a well lot the system needs its own tank and pump. Our sister company, Maryland Fire Sprinklers, designs, permits and installs them.
A licensed builder for your Charles lot
Send the address and the kind of unit. We check it against the Charles rule and the sprinkler question, then connect you with a licensed Maryland builder who already does ADUs here.