Key Facts Ordinance Text Full Breakdown Violations FAQ Sources More in Howard County

Howard County, MD Accessory Structures: ADU Rules (2026)

Some Restrictions

Compiled from the official code textEditor Martyn O'NeillLast verified September 2026

ADU rules in Howard County, MD, also called accessory dwelling unit regulations or granny flat ordinances, cover setbacks, owner-occupancy, parking, and permit requirements.

Key Facts

Permit: Planning and Zoning permit required
Owner occupancy: Owner lives in principal or ADU
New max size (CB 3-2026): 75% of principal footprint
Number allowed: One per single-family lot
Short-term rental: Not permitted

ADU Eligibility Quick-Check

An Accessory Dwelling Unit (ADU) is a smaller, independent living unit on the same lot as a single-family home: converted garages, detached cottages, basement or attic conversions, and attached additions all qualify. Most states have streamlined ADU permitting since 2020, but local rules still control size, height, and setback.

Is your lot zoned single-family or multi-family residential?
Does your lot have at least 1,200 sq ft of buildable space?
Is your existing home owner-occupied (in most states this is not required, but some require it for ADU permits)?
Will the ADU stay under your state's size cap (commonly 850-1,200 sq ft for detached)?
Can you provide one off-street parking space (waived in many states within 0.5 mi of transit)?

If you answered 'yes' to most of these, you likely qualify in Maryland under recent ADU streamlining laws. The Howard County, MD rules below cover local size, height, and setback requirements.

Summary

Howard County permits an accessory dwelling unit inside an owner-occupied single-family home. The owner must live in the principal dwelling or the ADU, and a permit from the Department of Planning and Zoning is required. Recent Council Bill 3-2026 expanded ADU options countywide.

These county ordinances apply to unincorporated areas of Howard County. Incorporated cities within the county may have their own rules that take precedence over county-level regulations.

The accessory apartment must be located within an owner occupied dwelling. The owner may occupy either the principal dwelling or the accessory apartment... In all dwellings, an accessory apartment shall occupy no more than one-third of the net floor area of the building, up to a maximum of 1,500 square feet.

View official code

Official source re-checked September 7, 2026: no newer edition of the code had been published (publisher’s edition: Code of Ordinances: Supplement 91 | Zoning: Supplement 25).

Full Breakdown

Under Howard County Zoning Regulations Section 128.0.13, an accessory apartment must be located within an owner-occupied dwelling, and the owner may occupy either the principal dwelling or the accessory apartment. Historically it could occupy no more than one-third of the building's net floor area, up to 1,500 square feet, operating only under a Department of Planning and Zoning permit. Council Bill 3-2026 (ZRA-218), effective April 8, 2026, modernized the rules: an ADU may not exceed 75% of the principal dwelling's exterior footprint, only one detached or attached ADU is allowed per single-family lot, ADUs may not be used as short-term rentals, and off-street parking increases.

Violations & Fines

Building or renting an ADU without the required Planning and Zoning permit, or using it as a short-term rental, is a zoning violation subject to enforcement and permit revocation.

Frequently Asked Questions

Can I rent my ADU on Airbnb?

No. Under Council Bill 3-2026, accessory dwelling units in Howard County may not be used as short-term rentals. They are intended for long-term occupancy on owner-occupied lots.

Do I have to live on the property?

Yes. Section 128.0.13 requires the accessory apartment to be within an owner-occupied dwelling, and the owner may live in either the principal dwelling or the ADU.

Sources & Official References

Other rules in Howard County

Parking Rules: Street Parking LimitsSome Restrictions Shed & Carport RulesSome Restrictions ADU Rental RestrictionsSome Restrictions ADU Owner OccupancySignificant Restrictions Garage ConversionsSome Restrictions Tiny HomesSome Restrictions Parking Rules: Snow Removal Parking RulesSignificant Restrictions Parking Rules: Commercial & Oversized VehiclesSome Restrictions Parking Rules: Loading ZonesSome Restrictions Parking Rules: Curb Color RulesSome Restrictions Parking Rules: EV ChargingSome Restrictions

All Howard County rules

How Howard County compares: Easiest Cities to Build an ADU·Compare Howard County to another location·View the Maryland accessory structures overview

See something wrong?

Help us keep this page accurate. If you notice an error or outdated information, let us know.