Montgomery County ADU Rules 2026: ZTA 26-06 in Effect

Montgomery County’s updated ADU zoning rules took effect October 5, 2026. The Council adopted Ordinance No. 20-36 (ZTA 26-06) on September 15, 2026, changing ADU size limits, eligible zones, setbacks, density treatment and parking standards. The separate owner-occupancy and affordable-ADU fee proposal, Bill 41-26, remains pending.

Jurisdiction check: A Montgomery County mailing address does not always mean County zoning controls. Rockville, Gaithersburg and several other municipalities exercise their own planning authority, while Takoma Park adds City review layers to the County framework. Check the property address in the Maryland ADU Jurisdiction Finder →

The starting point for a new project is the adopted ordinance and DPS guidance revised October 5, 2026. Older materials may still describe the superseded 2019 size limits. Confirm the applicable zone, measurements and any existing approval or qualifying older-structure exception with DPS before committing to a design. Our Montgomery County setback guide provides related parcel-planning context; where older summaries conflict, use the adopted ordinance and current DPS instructions.

Research record: Adopted ZTA 26-06 and current DPS implementation guidance checked October 22, 2026 (UTC). Status: Enacted and effective October 5, 2026. The signed Council copy is Ordinance No. 20-36, adopted September 15, 2026. Separately, the official Bill 41-26 record lists Worksession as of October 23, 2026 (UTC), with an October 21 staff report for the scheduled October 26 PHP Committee worksession. No enactment or effective date is shown. Its proposed owner-occupancy removal and affordable-ADU fee relief are not current law.

Your next 3 actions in Montgomery

Confirm who controls zoning. Use the Jurisdiction Finder; municipal boundaries and licensing exceptions matter.
Confirm the adopted rule and measurement basis with DPS. ZTA 26-06 is effective. Ask how the 75% size standard, your zone’s accessory-structure limits and any qualifying older-structure exception apply to your proposal.
Contact DHCA before construction. Its Class 3 guidance calls for licensing even if the ADU will not be rented. Confirm the correct municipal licensing route where relevant.

Check the shared research record and source history · Continue your property checklist

Montgomery County ADU status at a glance

Question	Current rule after October 5, 2026	Important qualification
Status	ZTA 26-06 is enacted as Ordinance No. 20-36, adopted September 15, 2026 and effective October 5, 2026.	Bill 41-26 is a separate pending licensing and fee proposal.
Attached and detached ADU size	The general definition limits an ADU to 75% of the size of the primary single-family detached dwelling, subordinate in use to it.	The former attached-size rule and detached three-part cap were deleted. Confirm the measurement basis and any qualifying older detached-structure exception with DPS.
Setbacks, height and lot coverage	Accessory-structure standards in the underlying zone apply.	The detached-ADU-specific setback provisions were deleted. Certain legally built pre-May 31, 2012 structures retain an exception.
Parking	Outside the one-mile Metrorail, Purple Line or MARC station exemption, generally one ADU space is required in addition to required house parking.	If the house has no existing on-site parking, only the ADU’s one space is required. Hearing Examiner relief can address adequate street parking or a lot whose size or shape precludes extra on-site parking.
Eligible zones and dwelling type	Attached and detached ADUs are listed as limited uses across the non-Industrial zones in the amended use table.	The primary dwelling must be a single-family detached dwelling. Overlay rules, the AR transfer-of-development-rights restriction and other applicable standards still matter.
Number and occupants	One ADU per lot. Under the standard licensed route, no more than two ADU occupants may be age 18 or older; total occupancy is also governed by Chapter 26.	Older special-exception approvals have a separate retained branch in the use standards.
Short-term rentals	An ADU may not be on a lot where a Short-Term Residential Rental use exists or is licensed.	ZTA 26-06 retains this restriction.
Licensing and owner occupancy	The usual DHCA licensing and current owner-occupancy requirements remain.	The pending Bill 41-26 would change owner occupancy and certain affordable-ADU fees; do not treat those proposals as effective.

Source: Ordinance 20-36, pp. 4–9; current DPS guidance; Bill 41-26 status.

Where ZTA 26-06 stands now

Montgomery County introduced ZTA 26-06 on April 21, 2026 at the request of the Planning Board. The Council held a public hearing on June 9, and the Planning, Housing and Parks Committee reviewed the amendment on July 27.

The Council adopted ZTA 26-06 as Ordinance No. 20-36 on September 15, 2026. It became effective October 5, 2026, 20 days after adoption. The live Council index lists it as enacted, the ordinance cover records both dates, and the final page bears the Clerk’s certification of Council action. The October 2026 DPS guidance confirms implementation.

Official status sources: signed Ordinance No. 20-36 (ZTA 26-06), Council ZTA index and DPS ADU guidance revised October 5, 2026.

The biggest change: Montgomery’s ADU size limits

The adopted 75% size standard

The general ADU definition now requires the unit to be no more than 75% of the size of the primary single-family detached dwelling and subordinate in use to it. The definition covers attached and detached ADUs. Site coverage, setbacks, height, building-code requirements and any applicable exceptions must also be checked. Ordinance p. 5, Section 3.3.3.A.1.

The older size limits were removed

For detached ADUs, ZTA 26-06 deleted the rule limiting gross floor area to the smallest of 50% of the main dwelling’s footprint, 10% of lot area or 1,200 square feet. For attached ADUs, it deleted the separate 1,200-square-foot limit and basement/cellar-area alternative. Those deleted provisions should not be presented as the current formula for a new project. Ordinance pp. 8–9, deleted Sections 3.3.3.B.2.b and C.2.e.

A retained exception for some older detached structures

Section 3.3.3.C.2.b still permits a detached ADU in a structure legally constructed before May 31, 2012 without regard to setbacks or floor area if the structure is not increased in size or height and no new windows are added on the wall nearest an abutting property. DPS’s October guidance also identifies this exception. Ask DPS to confirm eligibility and how it applies alongside the general ADU definition before relying on it. Ordinance p. 8, lines 110–114.

Use our Maryland ADU Size Calculator & Measurement Guide as a planning aid, with the County-confirmed measurement basis and any applicable exception. A percentage alone does not establish a buildable project.

An unresolved question: what does “75% of the size” mean?

The adopted ordinance uses the phrase “75% of the size”. Neither that provision nor the October DPS guidance reviewed for this update supplies a complete measurement method specifying, for example, exterior footprint, above-grade finished area or total gross floor area. This is a measurement question about an effective rule, not an unresolved enactment question.

The deleted detached-ADU rule expressly used the main dwelling’s footprint; the new general definition uses size. Do not automatically carry the old footprint test forward or import another county’s method. Ask DPS which areas of the house and ADU count for your application, including basements and any proposed additions.

Planning takeaway: do not order a prefab unit solely from a 75% calculation. Confirm the measurement basis, site limits and any qualifying exception with DPS under the ordinance already in effect.

Parking after ZTA 26-06

For the standard licensed ADU route, a lot within one mile of any Metrorail, Purple Line or MARC Rail station is exempt from the ADU use standard’s additional parking requirement. Outside that exemption, provide one on-site space for the ADU in addition to any required on-site parking for the main dwelling, unless a waiver applies.

The adopted ordinance adds an important exception: if the principal dwelling has no existing on-site parking, the ADU only needs its own one required space. The earlier rule requiring at least two spaces when a new driveway was constructed for the ADU was deleted. Do not assume every property must create three spaces in total.

A Hearing Examiner may grant the Section 29-26(b) waiver on finding either adequate on-street parking or that the size or shape of the existing lot effectively prevents additional on-site parking. The latter ground was added by ZTA 26-06; it is not an automatic exemption.

Source: Ordinance pp. 5–6, Section 3.3.3.A.2.c.ii, lines 33–48.

Where ADUs are allowed and how approval works

The adopted use table lists both attached and detached ADUs as limited uses in the non-Industrial zones, including residential townhouse and multi-unit, commercial/residential and employment zones. This does not authorize an ADU inside any townhouse or apartment: the ADU definition still requires a primary single-family detached dwelling, and the attached/detached definitions refer to a detached-house building type. Industrial zones IL, IM and IH have no ADU permission in the amended table. Ordinance pp. 3–5 and 7–8.

The use table can be modified by overlay provisions. The retained AR-zone rule also allows an ADU to be prohibited under Section 3.1.5, Transferable Development Rights. Confirm the parcel’s zone, overlays and development-rights restrictions before assuming eligibility. Only one ADU per lot is permitted.

For the standard licensed route, the ADU must share the main dwelling’s street address. Occupancy remains subject to Chapter 26, Section 26-5, with no more than two ADU occupants age 18 or older. The ordinance retains a separate branch for accessory apartments approved as special exceptions before May 20, 2013 that satisfy their approval conditions. These are retained provisions, not new exemptions created by ZTA 26-06. Ordinance pp. 5–7, Section 3.3.3.A.2.

ADUs are now excluded from density calculations across zones. If a property is later subdivided so the detached ADU stands on its own lot, the unit counts in density calculations. This provision does not itself approve subdivision. Ordinance p. 7, Section 3.3.3.A.2.e.

An ADU must meet the setback, height and building-lot-coverage standards for accessory structures in the underlying zone, subject to the retained older-structure provision discussed above. The special detached-ADU setback language and extra setback for dimensions exceeding 24 feet were removed. An attached ADU’s separate entrance must be at the side or rear, unless the front entrance existed before May 20, 2013 or a single front entrance door serves both the main dwelling and the ADU. Ordinance pp. 6–9.

Limited-use zoning does not remove the DHCA licensing, DPS permit or applicable waiver steps. DPS directs applicants to begin the ADU licensing process with DHCA before applying for the building permit. Parking-waiver requests can still go to the Hearing Examiner. See current DPS licensing and permitting instructions.

After zoning: Montgomery County Class 3 ADU licensing

Montgomery County adds a separate DHCA licensing step that homeowners should plan for early. The current DHCA Class 3 page directs ADUs without a special exception approved before May 20, 2013 to apply for a Class 3 license. Under that route, County guidance calls for licensing whether or not the ADU will be rented and before advertising it for rent. Owners with an older special-exception approval should confirm their applicable licensing route and approval conditions with DHCA. Zoning compliance alone does not complete licensing or permitting.

Class 3 step	What Montgomery County currently requires
1. Apply to DHCA	Submit the Class 3 ADU application with proof of residency and the owner affidavit. The current detailed DHCA requirements sheet calls for an ADU plan on 11×17-inch paper at ¼-inch-per-foot scale, with room dimensions and key building details, plus a separate driveway plan with dimensions.
2. Completeness review	The current detailed DHCA requirements sheet says the application is reviewed for completeness within 10 business days of receipt.
3. Public notice	After the application is accepted, the owner must post the public-notice sign within 5 days. The sign must remain posted for at least 30 days and until the initial inspection is complete.
4. Inspection and Director’s report	Housing Code Enforcement inspects the property. DHCA then issues a preliminary report and, after final inspection, a final report.
5. Permit coordination	County guidance says construction, alteration or renovation should not begin before DHCA’s preliminary inspection report is completed, and open permits must be finalized before the license is issued.
6. License	Current DHCA guidance says the ADU license is approved 30 days after the Director’s Report, subject to compliance and any additional time needed to correct deficiencies.

Parking waiver: A property that does not meet the current on-site parking requirement may still apply for the Class 3 license and seek a waiver through the Office of Zoning and Administrative Hearings. Current DHCA guidance also states that on-site ADU parking is not required when the property is within one mile of a Metrorail, Purple Line or MARC station.

Takoma Park is a licensing exception. Current County materials say properties inside the incorporated City of Takoma Park do not pay the County annual rental-license fee and obtain the rental license through the City of Takoma Park.

Fee documents currently conflict

Montgomery County’s current rental-license fee webpage and its detailed Class 3 requirements sheet both list $615 due with a Class 3 ADU application ($260 filing + $230 sign + $125 annual license). However, a separate County-hosted application form still lists $612 ($260 + $230 + $122). We therefore use $615 as the stronger current planning figure, but homeowners should still verify the amount with DHCA Licensing immediately before submitting payment.

Montgomery County DHCA — Class 3 ADU licensing portal · Current rental-license fee page.

Owner occupancy and the separate pending Bill 41-26

Separate pending proposal: Bill 41-26, introduced September 15, 2026, would remove the ADU rental-license owner-occupancy requirement and create specified fee relief for ADUs rented at levels affordable to households earning 65% or less of area median income for at least 10 consecutive years under an agreement with DHCA. The official record lists Worksession as of October 23, 2026 (UTC), with no enactment or effective date shown. The staff report dated October 21, 2026 is for the scheduled October 26 PHP Committee worksession; check the current agenda before attending. Owner-occupancy alternatives remain under consideration; none is enacted. ZTA 26-06’s enactment did not enact Bill 41-26.

Montgomery County’s current ADU requirements state that either the principal dwelling or the ADU must be the owner’s primary residence. This allows an owner to live in the ADU and rent the main house, or live in the main house and rent the ADU, subject to the applicable licensing rules.

The practical result is that the existing ADU rental-license framework is not designed for an absentee owner renting both dwellings simultaneously. Always confirm the current DHCA licensing requirements when your project involves rental income.

Montgomery County DHCA — current Class 3 ADU application process and requirements.

Short-term rentals and Airbnb

A Montgomery County ADU cannot be operated as a short-term residential rental. DHCA’s Class 3 ADU requirements prohibit Airbnb and other short-term residential rentals on a property with an ADU.

The adopted zoning rule bars an ADU from any lot where a Short-Term Residential Rental use exists or is licensed. This is broader than restricting only the ADU itself. ZTA 26-06 retains the rule. Ordinance p. 7, Section 3.3.3.A.2.d.

Montgomery County DHCA — Class 3 ADU requirements (PDF page 3).

What homeowners should do under the updated rules

Confirm the reviewing jurisdiction and parcel zone. County mailing addresses do not establish zoning authority. Check overlays, AR development-rights restrictions and any earlier special-exception approval.
Use the adopted size standard. Ask DPS to confirm the 75% measurement basis; do not use the deleted 10%-of-lot, 50%-of-footprint and 1,200-square-foot formula as the current new-project limit.
Check accessory-structure site limits. Confirm setbacks, height and building lot coverage. If converting a legally built pre-May 31, 2012 detached structure, ask about the retained exception before changing its size, height or windows.
Check transit proximity and existing parking. Confirm the one-mile rail-station exemption, the rule for a main dwelling with no existing on-site parking, and whether a Hearing Examiner waiver is needed.
Plan for licensing and permits. Contact DHCA before applying for the DPS building permit. Confirm the correct licensing route, current owner-occupancy rules, fees and any municipal requirements.
Check private well and septic capacity early. If the property uses private systems, use our Maryland ADU Septic & Well Readiness Guide before final design.
Keep Bill 41-26 separate. Its proposed owner-occupancy removal and affordable-ADU fee waivers remain pending; verify any later enactment and effective date before relying on them.

Municipality ADU guides in Montgomery County

Several municipalities exercise their own zoning or add a separate city review layer. Use the local guide when the property is inside:

Next steps for Montgomery County homeowners

If this is your jurisdiction, stay focused on this county’s rules rather than comparing unrelated Maryland counties. Once the local rule path is clear, move through the project in this order:

Already ready to speak with a professional? Prepare a Maryland ADU project request →

Primary sources used for this guide

For Maryland’s statewide baseline, read our Maryland ADU Guide 2026. For county-by-county implementation status, use the Maryland County ADU Rules Tracker. Before signing a builder or prefab contract, review our Maryland ADU Cost Escalation Guide to identify site, utility, permitting and scope items that can sit outside a headline quote. Maryland ADU Guide is maintained by Gijo John; source-backed corrections can be sent to gijo.j@marylandaduguide.com.

YOUR NEXT PRACTICAL STEP

What to do next

Start by finding the office that reviews your property. A mailing city or a county guide does not establish your parcel’s authority.

Find Who Reviews My Property.
Obtain your parcel identifier, survey, floor plans and utility records.
Ask the reviewing office which current rules, supporting documents and approvals apply.
Continue to your planning workspace.

Enable JavaScript to prepare a downloadable next-step brief. Planning guidance is not permit approval.