Building permits, zoning and septic rules in Montgomery County, Maryland

Yes. Montgomery County requires a permit before you build a detached one- or two-family home or a townhouse up to three stories above grade with its own exterior entrance, and Right-of-Way and Sediment Control applications must accompany the building-permit application¹. If you hold title to the land and will build your own personal residence yourself, county law lets you pull the permit as an owner-builder, though you give up New Home Warranty and Home Builder Guaranty Fund protection¹⁰. A structure used exclusively for agriculture on land assessed for agricultural use is exempt from the building permit itself, but it still needs any electric, well and septic permits¹¹. Montgomery County has adopted the 2021 International Code Council package with local amendments for commercial construction; the adopted package also includes the 2021 NFPA fire and life-safety codes with Maryland amendments¹².

The Montgomery County Department of Permitting Services (DPS) is the building department; reach the main office at 2425 Reedie Drive, 7th Floor, Wheaton, MD 20902, phone 240-777-0311¹³. DPS coordinates the building, right-of-way, sediment-control and other permit reviews for a new home, with a four-week commitment for its code review before required WSSC and M-NCPPC approvals are complete¹. Permit costs vary by application: a filing fee is generally due when you apply, the balance is generally due before issuance, and the county adjusts its operating-cost factor each July 1¹⁴. Well and septic applications go through DPS Well and Septic separately; call 240-777-6306 to schedule an inspection⁵.

Yes, countywide, through the Montgomery County Zoning Ordinance (Chapter 59); look up the property's zoning district, then check that district's standards in Chapter 59². Brookeville, Poolesville, Laytonsville, Rockville, Barnesville, Gaithersburg and Washington Grove are exempt from the county ordinance, so parcels there need the municipality's rules³. Rural dimensions depend on the mapped zone: RDT regular lots cap coverage by roofed buildings and structures at 10%, while RE-1 lots cap it at 15%; both cited district standards cap principal-building height at 50 feet, with agricultural buildings exempt from the RDT height cap^15,16. Setbacks follow the mapped zone too: in RE-1 the principal-building minimums are 50 feet front, 17 feet side and 35 feet rear, while R-60 lots need 25 feet front, 8 feet side and 20 feet rear, and accessory structures must sit behind the principal building's rear building line^17,18. A manufactured or mobile home for residential use is limited to designated mobile-home zoning districts, so it is not automatically allowed on an ordinary rural parcel⁹.

DPS Well and Septic is the approving authority for septic systems in Montgomery County, working alongside Maryland Department of the Environment requirements⁴. A septic permit is required to serve a new home or to upgrade an existing system for an addition, runs for 12 months with one 6-month extension available, and is usually issued within about two weeks of a complete application⁵. Once installation starts, the county requires a minimum of two inspections before it will approve the system⁵. Soils are the real constraint here: only about 14% of Montgomery County's soils lack severe limitations for a conventional drain field, so a site evaluation matters before you buy⁶. Where a non-conventional system is needed, the county describes an approved pretreatment or aerobic treatment unit, engineered by a qualified professional and monitored by DPS and MDE for at least two years after startup⁴.

Montgomery County expressly describes a tiny home as one possible accessory dwelling unit, but that unit must share a lot with a single-family detached house; it is not permitted with a townhouse, condominium, duplex or mobile home⁸. Residential use of a manufactured or mobile home is limited to designated mobile-home zoning districts, so confirm the parcel's mapped district before treating one as a homesite option^2,9. We could not confirm a complete countywide rule for using an RV as the sole residence on every vacant rural lot outside a campground or licensed park. Ask the Montgomery County Planning Department's zoning information counter about the exact parcel and proposed occupancy before buying¹⁹.

1. Confirm the property's zoning district and Chapter 59 standards before design begins².
2. Line up the well permit if the lot lacks public water and the septic permit if it lacks public sewer^5,7.
3. Apply for the building, Right-of-Way and Sediment Control permits together; DPS commits to a four-week code review, while WSSC and M-NCPPC approvals have separate timing¹.
4. Resolve any Floodplain District permit before construction; new residential building is prohibited in the mapped 100-year floodplain²⁰.
5. Post the construction sign within 3 days after permit issuance, have it verified before work begins, and request each residential inspection at least 24 hours before it is needed^1,21.
6. Pass the required building and septic inspections; a new home cannot be occupied until DPS issues its Residential Use and Occupancy certificate after the final inspection^5,22.

Water and waste: public water and sewer are generally available in higher-density areas and major transportation corridors, while lower-density suburban and rural areas usually rely on permitted private wells and septic systems^5,7,23. Soils: only about 14% of Montgomery County soils lack severe limits for a conventional drain field, so make septic feasibility and system design part of due diligence⁶. Flood risk: new residential construction is prohibited in the mapped 100-year floodplain, and development in the Floodplain District requires a county permit plus applicable state and federal approvals^20,24. Access: a driveway that connects to a Montgomery County road needs a county driveway permit, while a driveway on a state or municipal road needs a permit from that jurisdiction instead²⁵. Single-family lots are generally limited to one driveway entrance per street, and a second may be considered case by case for frontage of 90 feet or more²⁶. Work in a state right-of-way also requires coordination with the MDOT State Highway Administration district office²⁷. Taxes: the effective property-tax rate is about 0.9%, and the median annual bill is about $5,341⁶. Montgomery County averages about 2,147 people per square mile, and the nearest city of 100,000 or more is about 21 miles from the county center⁶.