Howard County’s new ADU rules are in effect. Council Bill 3-2026 (ZRA 218) was signed in February 2026 and became effective on April 8, 2026. It expands where attached and detached accessory dwelling units can be created and replaces the county’s older accessory-apartment framework.
This guide explains the current Howard County rules, including the unusual 75%-of-exterior-footprint size calculation, owner-occupancy requirement, short-term-rental ban, permit process, and a parking discrepancy we found between Howard County’s summary webpage and the final enacted bill. For the statewide comparison, see our Maryland County ADU Rules Tracker.
Last verified: September 6, 2026. This page is informational and is not legal, zoning, architectural, engineering, or permitting advice.
Howard County ADU rules at a glance
| Question | Verified Howard County rule |
|---|---|
| Effective date | CB 3-2026 became effective April 8, 2026. |
| ADU forms | Attached and detached ADUs are allowed in qualifying districts; existing space may also be renovated to create an attached ADU. |
| Maximum size | Maximum ADU size is 75% of the exterior footprint of the principal dwelling. |
| Owner occupancy | The property owner must reside in either the principal dwelling or the ADU. |
| Short-term rentals | Prohibited. The enacted amendment defines a short-term rental as lodging for fewer than 30 consecutive days for compensation. |
| Parking | The final amended bill shows 1.0 additional off-street space per ADU. Howard County’s current ADU webpage says three spaces with exceptions. See the source-conflict section below. |
| ADU permit | Zoning approval is required through the Department of Planning and Zoning before the ADU may operate. |
| Application fee | Howard County currently lists a $25 ADU application fee. |
What CB 3-2026 changed
Howard County describes CB 3-2026 as an expansion of ADU opportunities intended to align local zoning with HoCo By Design, the Housing Opportunities Master Plan, and Maryland’s statewide ADU law. The county says single-family homeowners may construct attached or detached ADUs or renovate existing space to accommodate an attached ADU in various residential zoning districts.
The enacted framework also limits the number and type of ADUs by the principal dwelling. Howard County’s summary of the adopted amendments states that a lot developed with a single-family detached dwelling is limited to one detached or attached ADU, while a lot developed with a single-family attached or semi-attached dwelling is limited to one attached ADU. ADUs are prohibited on lots developed with two-family dwellings.
Official source: Howard County Department of Planning and Zoning — Accessory Dwelling Units.
The footprint calculation: how large can your Howard County ADU be?
Howard County does not describe the limit as 75% of the home’s total finished living area. Its current FAQ says the maximum allowable ADU size is calculated from the exterior footprint of the principal dwelling, and the accessory unit may not exceed 75% of that footprint.
Use our Maryland ADU size calculator to see how Howard County’s footprint method differs from Maryland’s statewide finished-living-area guidance.
That distinction can materially change a project. A two-story house may have substantially more interior floor area than ground-level footprint.
Lot coverage and stormwater can reduce what fits
The 75% calculation is a maximum-size rule, not a guarantee that the entire theoretical area can be built. Howard County’s adopted-ADU materials also apply lot-coverage standards to detached accessory structures, including ADUs.
For an ADU in a newly constructed structure, the county’s application page requires the plot plan to demonstrate adequate water conveyance so the project does not adversely affect neighboring properties or existing subdivision stormwater-management facilities.
Owner occupancy is required
Howard County requires the property owner to reside in either the principal dwelling or the ADU. The county’s application guidance states that an owner who wants to rent the other dwelling must first obtain zoning approval for the ADU.
If either the principal dwelling or the ADU will be rented, a rental license may also be required through the Department of Inspections, Licenses and Permits. Howard County’s current application guidance says the owner must obtain ADU zoning approval before applying for the rental license.
Short-term rentals are prohibited
CB 3-2026 was amended to prohibit ADUs from being used as short-term rentals. The enacted amendment defines a short-term rental as a dwelling, or part of one, used for lodging for fewer than 30 consecutive days in exchange for compensation, and specifically references platforms such as Airbnb and VRBO as examples.
So an ADU project intended primarily for nightly or weekly visitor accommodation should not be treated as a compliant Howard County ADU rental strategy.
Parking: an important conflict in Howard County’s own sources
This is the most important source discrepancy we found while reviewing Howard County’s 2026 materials.
Howard County’s current ADU webpage says one of the adopted amendments was an increase of off-street parking per ADU from one space to three spaces, with exceptions. However, the final amended CB 3-2026 text published through the County Council’s legislation system still shows 1.0 additional off-street parking space per accessory dwelling unit.
The legislative record explains the mismatch. Proposed Amendment 10 would have changed the requirement from one space to three and would have allowed DPZ to reduce the requirement when adequate on-street parking existed in front of the parcel, while preserving a minimum of one off-street space. But the County Council’s February 2, 2026 session minutes state that Amendment 10 was not moved.
Primary records: CB 3-2026 legislation record, final amended CB 3-2026 text, and February 2, 2026 Council session record.
How to apply for a Howard County ADU
Howard County requires an ADU application through the Department of Planning and Zoning. The application must include a plot plan showing compliance with the applicable maximum size and setback requirements.
For a newly constructed ADU structure, the plot plan must also address water conveyance and potential effects on neighboring property or subdivision stormwater facilities. Howard County currently lists the ADU application fee as $25.
Howard County ADU application and current instructions.
Before paying for ADU plans: a Howard County checklist
- Confirm the zoning district. Verify that the proposed ADU form is allowed on your property.
- Establish the exterior footprint. Do not use total multi-story living area as a substitute for Howard County’s footprint calculation.
- Calculate the 75% ceiling. Then test that number against setbacks, lot coverage and site constraints.
- Check water and sewer or well and septic. Resolve capacity questions before committing to plans. If the property uses private systems, use our Maryland ADU Septic & Well Readiness Guide before final design.
- Review drainage. A new detached structure must demonstrate adequate water conveyance.
- Confirm parking directly with DPZ. The county webpage and final legislative record currently conflict.
- Plan for owner occupancy. The property owner must reside in one of the two dwellings.
- Do not plan on Airbnb or VRBO. ADU short-term rentals are prohibited.
- Budget for the permit sequence. Zoning approval comes before operation of the ADU and before a rental-license application when one is required.
Primary sources used for this Howard County guide
- Howard County Planning & Zoning — ADU portal
- Howard County Council — CB 3-2026 legislative record
- CB 3-2026 final amended text
- County Council February 2, 2026 session record
- Howard County ADU application
Maryland ADU Guide is maintained by Gijo John as an independent research publication. See our Editorial & Research Policy for how regulatory content is sourced and updated. Corrections supported by official records can be sent to gijo.j@marylandaduguide.com.