Maryland ADU Guide 2026: HB 1466 Rules, Size, Setbacks & Local Requirements

Yes—Maryland law requires counties and municipalities with planning and zoning authority to adopt a local law authorizing ADUs by October 1, 2026. House Bill 1466, now Chapter 197 of the 2025 Laws of Maryland, took effect October 1, 2025, but it did not create one automatic statewide permit on that date. Until a conforming local law takes effect, follow the current county or municipal approval process and verify that any proposed legislation has actually been enacted. If your jurisdiction is still transitioning, see what the October 1 deadline does—and does not—change.

The important point for homeowners is that Maryland now sets a statewide floor, but your exact approval path still depends on the local jurisdiction. This guide separates what the state law requires from what counties and municipalities may still control. For current local implementation, use our Maryland County ADU Rules Tracker. If you are not certain which county or municipality actually controls the property, start with the Maryland ADU Jurisdiction Finder, then carry that result into the Maryland ADU Property Feasibility Checker for the property-level screen.

Statewide framework independently rechecked: September 20, 2026. This page is informational and is not legal, zoning, architectural, engineering, tax, or permitting advice.

Maryland ADU law in 2026: what HB 1466 changed

Questions Maryland homeowners are actually asking

Why these questions are here: We reviewed 133 substantive comments visible in Instagram’s loaded/relevant-comments view on a Maryland ADU Reel to identify the issues residents were repeatedly confused or concerned about. Social discussion is used here to discover questions—not as legal authority. The answers below are checked against Maryland legislation, Maryland Department of Planning guidance, SDAT material and local rules where applicable. No commenter identities are reproduced.

Will an ADU increase my Maryland property taxes?

It can. Maryland does not impose a special statewide “ADU tax,” but SDAT considers new improvements and renovations when valuing residential property. A qualifying permit can also trigger an out-of-cycle assessment. See our Maryland ADU property-tax and assessment guide for the reassessment timing, Homestead Credit rules and a worked example.

Can my HOA still stop me from building an ADU?

HB 1466 prohibits deeds, declarations, HOA bylaws and similar private instruments from imposing an unreasonable limitation that effectively prevents a qualifying owner from developing an ADU or offering it for rent. That does not erase every HOA rule, and restrictions on short-term rentals can still be valid. Read the Maryland ADU HOA rules guide before relying on a summary of your covenants.

Can a county use setbacks to make an ADU practically impossible?

Maryland places a real limit on this: a local ADU law may not establish side or rear setbacks that exceed the jurisdiction’s existing setbacks for accessory structures. That is not a universal statewide setback number; the underlying accessory-structure standard remains local.

Can I use a Maryland ADU as an Airbnb or short-term rental?

HB 1466 does not create a statewide right to operate an ADU as a short-term rental. Maryland Department of Planning states that the law does not alter local governments’ power to regulate short-term rentals, and the HOA provisions specifically allow short-term-rental restrictions to be treated differently from an outright ADU ban. Check the current county or municipal rule before underwriting Airbnb income.

Does an ADU automatically get a separate address, mailbox or utility meter?

No statewide rule in HB 1466 answers those questions for every property. Address assignment, emergency addressing, mail delivery, utility service, meter configuration and connection requirements can involve different local agencies and utility providers. Treat them as project-verification items rather than assuming “detached ADU” automatically means a second address or meter.

What if the property is in a historic district?

Historic properties require separate review. Maryland Planning notes that the law’s private-restriction provisions contain an exception for certain historic properties, and local historic-preservation review can still affect design and approval. Use the Maryland historic-district ADU guide to distinguish local design review, Register status and the HB 1466 private-restriction rule.

What about waterfront, Critical Area, flood or environmental restrictions?

HB 1466 does not wipe away environmental, public-health or facility-capacity rules. Maryland Planning specifically recommends continued compliance with existing environmental and facility-capacity laws. Waterfront and Critical Area properties therefore need overlay-specific verification in addition to the basic ADU zoning check. Our Maryland ADU floodplain guide explains the separate map, permit, elevation and conversion checks. Use the Maryland Critical Area ADU guide for the RCA 900-sq-ft density rule, Buffer and lot-coverage checks.

What if the ADU already exists or was never permitted?

HB 1466 is silent on existing ADUs. Maryland Planning recommends recognizing legally existing units, but the law does not automatically legalize an unpermitted apartment or backyard unit. Use our existing and unpermitted Maryland ADU guide to separate legal-existing, nonconforming and legalization issues.

Can I convert a garage, barn or other accessory building into an ADU?

Maryland Land Use §4-504(a)(2) expressly contemplates full or partial conversion of an accessory structure and allows a local law to prohibit that conversion when its only vehicular access is from an alley. The conversion still has to satisfy the applicable local approval, building, safety, utility and site rules. This conversion language is in §4-504, not the enacted ADU definition in §4-501.

Can I build several ADUs on a large Maryland parcel?

Do not assume a large parcel creates a statewide right to multiple ADUs. HB 1466 establishes the statewide ADU framework, but the exact number and approval path still need to be checked against the controlling local ordinance.

Can I operate a salon or another business from the ADU?

HB 1466 is not a statewide home-business authorization. Home occupations, client visits, signage, parking and commercial activity are typically governed through local zoning or licensing rules. Verify the business use separately from whether the structure qualifies as an ADU.

Are permits, septic review and utility checks still required?

Yes. The state law requires local ADU frameworks to preserve public health, safety and welfare standards, including relevant building codes and adequate public facilities provisions. Properties on private well or septic should use our Maryland ADU septic and well guide early in feasibility.

How much does a Maryland ADU actually cost?

There is no responsible single statewide price. Site work, structure type, utilities, septic, design, permits and project delivery can move the total dramatically. Our Maryland ADU Cost Calculator & Contractor Bid Comparison separates those scopes instead of presenting one headline number as an “average.”

Do counties and municipalities still make their own ADU rules?

Yes. Maryland establishes the statewide floor, but local governments still determine major implementation details within that framework. During the 2026 transition, proposals and enacted rules can change quickly. Use the Maryland County ADU Rules Tracker rather than assuming a statewide summary answers the local permit question.

Does this include Baltimore City?

Baltimore City should be treated as its own jurisdiction for ADU research, not as “Baltimore County.” Maryland’s statewide framework and Land Use Article are the starting point, but homeowners need to verify Baltimore City’s own zoning, building and implementation rules for the actual approval path.

What counts as an ADU in Maryland?

Maryland defines an accessory dwelling unit as a secondary dwelling unit located on the same lot, parcel or tract as a primary single-family detached dwelling. The ADU may be attached to the house or located in a separate structure.

The Maryland Department of Planning also notes that jurisdictions may permit ADUs located entirely within the existing home, even though the statute does not separately define that configuration.

Official source: Maryland Department of Planning — HB 1466 ADU FAQ.

The 75% ADU size rule

Under HB 1466, an ADU may be up to 75% of the size of the primary single-family detached dwelling. Maryland Department of Planning guidance states that because local jurisdictions must authorize ADUs consistent with the state definition, a jurisdiction may not impose an ADU size cap below that 75% threshold.

The statute does not specify exactly how the primary dwelling should be measured for this calculation. Maryland Department of Planning recommends using the square footage of finished living area above grade. That recommendation is guidance rather than a substitute for the local ordinance or permit office’s measurement rules.

Use our Maryland 75% ADU size calculator and measurement guide to compare the statewide finished-living-area recommendation with Howard County’s exterior-footprint method.

Local approval can still vary

HB 1466 does not force every Maryland jurisdiction to approve ADUs by right. A county or municipality may authorize ADUs through a by-right process, conditional use, or special exception.

That distinction matters because a homeowner in one jurisdiction may have an administrative permit path while a homeowner elsewhere may face an additional review step. Before paying for design work, confirm the current local ordinance and the approval path that applies to your property. If you are still choosing a property, use our Maryland ADU pre-purchase due-diligence checklist before treating a listing as ADU-ready.

Density and residential-growth caps: the ADU is excluded

Maryland Land Use §4-504(c) requires a local ADU law to exclude development of the ADU from density calculations and from measures limiting residential growth that apply to the lot, parcel or tract.

In practical terms, a jurisdiction cannot count the ADU against a residential-density or growth-allocation cap on that property simply because it adds another dwelling unit. This does not waive building code, utilities, environmental overlays, setbacks or other property-specific requirements.

Setbacks: a statewide limit on local restrictions

A local ADU law may not establish side or rear setback requirements that exceed the jurisdiction’s existing setback requirements for accessory structures.

This does not create one universal Maryland setback number. It means the relevant local accessory-structure standard becomes the ceiling for side and rear ADU setbacks under the state framework. Use our Maryland ADU Setback Rules & Lookup Guide to compare the state ceiling with verified local examples.

Parking: study first, waiver required

A jurisdiction cannot simply add extra off-street parking requirements for ADUs without first completing a parking study. Maryland’s guidance says that study must consider factors including the cost of constructing parking, available curb space, added impervious surface and differences in lot size.

If a local law does impose additional ADU parking requirements, it must also include a waiver process. A jurisdiction that does not require additional off-street parking for ADUs does not need to complete the study. Use our Maryland ADU Parking Rules county-by-county tracker to see where we have located studies, waivers or no-extra-parking rules.

Utilities, septic, water and public-safety constraints still matter

HB 1466 does not erase building-code, public-health or infrastructure constraints. Local ADU laws must still provide for construction that meets relevant building codes and adequate public facilities requirements. For sprinkler, fire-separation, egress and conversion questions, see the Maryland ADU Building Code 2026 guide.

Land Use §4-504(b) preserves public-health, safety and welfare standards, including relevant building codes and adequate-public-facilities provisions. Water supply, sewage disposal and environmental hazards therefore need their own property-specific review. For properties on private well or septic systems, check capacity early.

Source correction — October 10, 2026: We corrected the statutory attribution for accessory-structure conversions and replaced a deleted proposal’s specific hazard list with the enacted health-and-safety provision. This correction does not mean that water, wastewater or environmental constraints disappear.

Use our Maryland ADU Septic & Well Readiness Guide to check capacity, reserve-area, perc-test and Health Department review questions before paying for plans.

Can a Maryland HOA block an ADU?

HB 1466 reaches beyond zoning. It also amended Maryland real-property law so that deeds, declarations, contracts, HOA bylaws and similar private instruments may not impose an unreasonable limitation on a qualifying property owner’s ability to develop an ADU or offer it for rent.

Maryland Department of Planning explains that an unreasonable limitation includes a restriction that prohibits development either explicitly or by its effect. The chaptered law also makes clear that a restriction on the short-term rental of an ADU is not treated as an unreasonable limitation for this purpose.

The law separately authorizes an HOA governing body to treat an ADU as a separate lot for purposes of HOA voting and assessments. That does not mean the ADU becomes a legally subdivided parcel; it is an HOA governance and assessment rule.

We cover this issue in detail in our dedicated Maryland ADU HOA guide.

Historic properties are a special case

The real-property restriction provisions include an exception for certain historic properties. Maryland Department of Planning advises homeowners and local governments to treat historic-property questions separately and to consult the applicable historic-preservation requirements.

How homeowners can use Maryland’s model ADU ordinance

Added September 14, 2026. MDP describes its Model Local ADU Ordinance & Assessment Tool as guidance for local governments implementing HB 1466. Its resource page dates the guidance to the law as of February 25, 2026. Treat the model as a comparison aid, not as an enacted ordinance for your address.

The assessment tool helps jurisdictions that already allow ADUs identify changes needed for minimum compliance. MDP says it does not cover the law’s Real Property Article changes or optional local provisions introduced by “may.” A completed assessment therefore does not answer every HOA, local-policy or property question.

Build a short comparison before contacting the zoning office

1. Identify the authority. Start with the Jurisdiction Finder and the applicable county or municipal guide.
2. Collect the adopted text. Record the ordinance number, amendment history and effective date. Keep proposed bill language in a separate column.
3. Compare one issue at a time. For size, setbacks, parking or approval procedure, note the state provision, the local provision and the specific question that remains. Read Land Use §4-504 alongside the guidance.
4. Request a written explanation. Ask the reviewing office which provision it applies to your proposal and how it reconciles any apparent conflict. Preserve its dated response with your records.

The statute retains building-code and public-health safeguards and allows different local approval procedures. It does not make downloading the model equivalent to receiving a building permit.

Does “Not Yet Verified” mean the county has broken the law?

No. On this site, that label describes a gap in our research. It is not a legal finding about a jurisdiction and does not mean ADUs are prohibited. For timing and unresolved local implementation, read the October 1 deadline guide. Record property-specific questions in the feasibility checker before committing to final plans.

What homeowners should verify before spending money

• Jurisdiction: Confirm whether your property is governed by the county, a municipality, or another zoning authority.
• Current ADU ordinance: Check whether the jurisdiction has already adopted its HB 1466-compliant rules.
• Approval process: Determine whether the ADU is by right, conditional use, or special exception.
• Primary-home size: Establish the measurement the local authority will use for the 75% calculation.
• Accessory-structure setbacks: These are critical because HB 1466 ties side and rear ADU limits to them.
• Water and sewer: Verify public utility availability or private well/septic capacity.
• Parking: Check whether the local ordinance imposes any additional requirement and, if so, how its waiver works.
• HOA documents: Review declarations, covenants and bylaws, especially if the property is association-governed.
• Historic status: Confirm whether the property is subject to historic-preservation review.
• Property tax: Review the current assessment and understand whether permitted improvements could trigger reassessment; see our Maryland ADU property-tax guide.

The October 1, 2026 deadline

The statewide policy has been effective since October 1, 2025, but local governments with planning and zoning authority have until October 1, 2026 to adopt compliant local laws authorizing ADU development.

That means Maryland is still in an implementation period. A county guide written six months ago may already be outdated, and a jurisdiction with an older ADU ordinance may still be revising it. Our local guides will therefore show a review date and link to the underlying local source rather than treating local rules as static.

Plan the budget and financing after feasibility

Once the state and local rule set is clear, build a realistic project budget with our Maryland ADU Cost Calculator & Contractor Bid Comparison. Add the possible assessment impact to your planning assumptions with our Maryland ADU property-tax guide. If you expect to borrow against the property or use a renovation mortgage, compare HELOCs, home equity loans, cash-out refinancing, FHA 203(k) and HomeStyle Renovation in our Maryland ADU Financing Guide.

Primary sources used for this guide

• Chapter 197, 2025 Laws of Maryland — HB 1466
• Maryland General Assembly — HB 1466 legislative history
• Maryland Department of Planning — HB 1466 FAQ
• Maryland Department of Planning — Model Local ADU Ordinance & Assessment Tool

Maryland ADU Guide is maintained by Gijo John as an independent research publication. See our Editorial & Research Policy for how regulatory pages are sourced and updated, and our Disclaimer for important limitations.

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.

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

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