Last researched: September 19, 2026. Preston has a real, current accessory dwelling unit provision in its municipal zoning code, but it is not a simple townwide “ADUs allowed everywhere” rule. The clearest ADU language appears in the Town’s Village Overlay Zone / Village Redevelopment Sub-Area, where an ADU can be approved by special exception, is limited to one per parcel in conjunction with a principal residential use, and is capped at 50% of the principal structure and no more than 1,500 square feet.
Homeowner takeaway: Preston’s posted ADU rule is useful, but it needs a 2026 state-law check. Maryland Planning now says covered jurisdictions may not impose an ADU maximum below 75% of the size of the primary single-family detached dwelling. Before paying for plans, ask Preston which current ordinance controls your parcel, whether the 50% cap has been amended, and whether your property actually lies in the overlay area where the ADU provision appears.
Preston ADU planning snapshot
| Question | What we verified |
|---|---|
| Local zoning authority | Preston has its own municipal zoning code, Planning Commission and Board of Zoning Appeals. |
| Current ADU location in code | The clearest ADU provision appears in Article VI, Overlay and Floating Districts, for the Village Overlay / Village Redevelopment framework. |
| Approval type | Accessory dwelling units are listed as a special-exception use in the applicable overlay tables. |
| Number of ADUs | One ADU per parcel when used with a principal residential use. |
| Local size rule | 50% of the principal structure, not to exceed 1,500 sq ft. |
| Density treatment | ADUs that rely on the same water connection are not counted in the overlay’s overall density calculation. |
| 2026 state-law issue | Maryland Planning says covered jurisdictions may not cap ADUs below 75% of the primary detached dwelling. |
| Accessory-structure setbacks | In R-1, larger accessory structures generally use 15-ft side/rear setbacks; in R-2, larger accessory structures use 8-ft side and 15-ft rear setbacks. Parcel zoning still matters. |
| Current 2026 new law found in eCode | The Preston eCode currently lists 2026 Ordinance 2026-O-1 for subdivision-law amendments, not an ADU zoning amendment. |
| County coordination | Caroline County agencies can still be involved in building, electric, plumbing, health or septic review after Town zoning approval. |
Preston’s ADU rule is tied to its Village Overlay framework
Preston’s municipal code does not present the ADU rule as a blanket use in every zoning district. The clearest language appears in Article VI, which governs the Village Overlay Zone and the Village Redevelopment Sub-Area.
Within that framework, the code lists:
- Accessory Dwelling Unit — size limited to 50% of the principal structure and not more than 1,500 square feet;
- one ADU per parcel when used with a principal residential use; and
- special-exception approval through the Board of Zoning Appeals.
That distinction is important. A Preston mailing address does not tell you that your parcel is in the applicable overlay area. Before using the ADU standards, confirm the parcel’s base zoning and overlay status with the Town.
The 50% / 1,500-sq-ft cap is the biggest 2026 issue
Preston’s posted overlay language limits an ADU to 50% of the principal structure and also sets a maximum of 1,500 square feet.
Maryland’s current statewide ADU framework uses a different ceiling. The Maryland Department of Planning says an ADU may be up to 75% of the size of the primary single-family detached dwelling, and covered jurisdictions may not impose a lower local maximum.
For a 2,000-square-foot primary dwelling:
- Preston’s posted 50% formula gives 1,000 square feet;
- Maryland’s 75% ceiling is 1,500 square feet.
For a 3,000-square-foot primary dwelling:
- 50% equals 1,500 square feet; and
- 75% equals 2,250 square feet.
The Town’s separate 1,500-square-foot absolute cap can therefore become more restrictive as the primary dwelling gets larger. That does not mean every large ADU is automatically approvable. It means the posted 50% / 1,500-square-foot ceiling should be checked against any later HB 1466 amendment before it is used as the final design limit.
Use our Maryland ADU size guide to understand the state framework, then ask Preston how it currently measures the primary dwelling.
A Preston ADU in the overlay is a special-exception use
The overlay table marks an ADU as SE, meaning special exception. Preston’s code defines the Board of Zoning Appeals as the body authorized to hear and decide special exceptions and variances.
Maryland’s HB 1466 guidance does not require every local government to make ADUs purely by-right. A jurisdiction may use a conditional-use or special-exception process to confirm compliance with objective local standards. The practical issue for Preston is whether the current special-exception criteria, timing and dimensional rules have been updated to match the state law.
Ask the Town what application, site plan, hearing notice and Board of Appeals steps apply to a current ADU request.
One ADU per parcel is explicit in the current overlay table
For a principal residential use, Preston’s Village Overlay table limits the parcel to one accessory dwelling unit. The same table also separately contemplates an ADU in conjunction with a principal commercial use, also by special exception.
That mixed-use language is a local distinction worth checking carefully. If your parcel is in a commercial or mixed-use setting, do not assume the residential ADU pathway is identical.
The same-water-connection density rule is unusually specific
Preston’s overlay code says accessory dwelling units that rely on the same water connection are not counted in the overall density calculation for the overlay.
That is consistent in direction with Maryland’s current rule excluding ADUs from residential-density calculations, but the local wording is tied specifically to shared water service. Ask Preston whether the 2026 implementation has broadened or clarified that provision.
Detached ADUs still need setback and lot-coverage review
Preston’s base zoning districts have their own accessory-structure standards. In the R-1 district, an accessory structure larger than 250 square feet generally must be at least 15 feet from side and rear lot lines. In R-2, the code generally uses an 8-foot side setback and a 15-foot rear setback for larger accessory structures.
Maryland now says local ADU side and rear setbacks may not be more restrictive than the jurisdiction’s existing accessory-structure setbacks. For a detached ADU, that makes the ordinary accessory-structure rule an important benchmark.
Do not apply the R-1 or R-2 numbers without checking the parcel. The Village Overlay sits on top of underlying zoning, and corner lots, lot coverage, building height and other provisions can still change the buildable envelope.
Preston’s code already contains a “mother-in-law suite” definition
The zoning definitions separately include a mother-in-law suite: rooms located under the roof of the main house, in an attached addition, or above an accessory structure such as a garage, intended for a related family member.
That older family-oriented concept is not the same thing as Maryland’s modern ADU definition. Maryland’s 2026 framework is not limited to relatives and is designed around a secondary independent dwelling unit.
If a Preston property already has or is proposing a mother-in-law suite, ask whether the Town will classify the project under that older definition, the ADU provisions, or both.
Caroline County can still be part of the permit path
Town zoning approval does not eliminate outside building and health requirements. Preston’s code references Caroline County electrical, plumbing and Health Department standards for residential units in parts of the zoning ordinance.
For an ADU, confirm which agency handles:
- building inspections;
- electrical permits;
- plumbing permits;
- septic review, if applicable;
- water and sewer service;
- fire-code review; and
- final occupancy approval.
For property outside Preston’s corporate limits, use our Caroline County ADU Rules guide instead.
We did not find a 2026 Preston ADU amendment in the current eCode new-law list
Preston’s current eCode is actively maintained. Its 2026 “New Laws” display currently shows Ordinance 2026-O-1, adopted May 4, 2026, concerning subdivision-law amendments. During this September 19 review, we did not find a separately identified 2026 ADU zoning amendment in that current new-law display.
That does not prove no ADU legislation is pending or recently adopted outside the indexed material. With Maryland’s October 1 deadline approaching, ask Town Hall whether an HB 1466 zoning amendment has been introduced, adopted but not yet codified, or scheduled for hearing.
What to ask Preston before paying for ADU plans
- Is the property inside the Village Overlay Zone or Village Redevelopment Sub-Area?
- What base zoning district applies underneath the overlay?
- Has the 50% / 1,500-square-foot ADU cap been amended for HB 1466 compliance?
- How does Preston measure the primary dwelling for Maryland’s 75% rule?
- Does the one-ADU-per-parcel rule remain unchanged?
- Is Board of Zoning Appeals special-exception approval still required?
- What findings must the Board make?
- What side and rear setbacks apply to a detached ADU?
- What building height and lot-coverage limits apply?
- What parking requirement and waiver process apply?
- Has the Town completed an ADU parking study if it requires additional off-street parking?
- Must the ADU use the same water connection?
- What utility-capacity or connection requirements apply?
- Which Caroline County building, electrical, plumbing or health approvals are required?
Preston homeowner checklist
- Confirm the property is inside Preston municipal limits.
- Identify the base zoning district and any Village Overlay designation.
- Ask Town Hall for the current ADU ordinance and any 2026 amendment.
- Do not design solely around the old 50% / 1,500-square-foot cap.
- Confirm the current 75% measurement method.
- Determine whether the project is internal, attached or detached.
- Verify accessory-structure setbacks, height and lot coverage.
- Confirm the Board of Zoning Appeals special-exception process.
- Check parking and any waiver process.
- Confirm water/sewer or septic requirements.
- Identify Caroline County trade or health permits that follow Town approval.
- Do not make a non-refundable construction commitment until the Town confirms the current rules.
Preston MD ADU FAQs
Does Preston allow ADUs?
Preston’s current zoning code expressly lists accessory dwelling units in its Village Overlay / Village Redevelopment framework. The use is subject to special-exception approval and the parcel must be in the applicable zoning context.
What is Preston’s ADU size limit?
The current posted overlay rule limits an ADU to 50% of the principal structure and no more than 1,500 square feet. Maryland Planning now says covered jurisdictions may not impose an ADU maximum below 75% of the primary detached dwelling, so ask Preston whether that local cap has been amended.
Can every Preston property have an ADU?
Do not assume so. The clearest ADU provision appears in the Village Overlay / Village Redevelopment rules. Confirm the parcel’s base zoning and overlay status with the Town before relying on the ADU table.
Does a Preston ADU require a special exception?
The current overlay table marks the ADU use “SE,” meaning special exception through the Board of Zoning Appeals. Confirm whether Preston’s final 2026 HB 1466 implementation changes that process.
Does an ADU count toward density in Preston?
The current overlay rule says an ADU that relies on the same water connection is not counted in the overall density calculation.
Who should I contact about a Preston ADU?
Start with the Town of Preston at Town Hall, 105 Backlanding Road, Preston, Maryland 21655. Maryland Planning currently lists the Town Manager as the municipal planning contact at 410-673-4929.
Primary sources checked
- Town of Preston — Article VI Overlay and Floating Districts
- Town of Preston — Article V District Regulations
- Town of Preston — Definitions and Word Usage
- Town of Preston — current eCode New Laws display
- Maryland Department of Planning — local planning contacts
- Maryland Department of Planning — HB 1466 ADU FAQ
- Maryland Land Use § 4-504
Maryland ADU Guide is an independent research publication, not the Town of Preston, Caroline County, a law firm, architect or contractor. Preston’s current code contains an explicit overlay-based ADU rule, but Maryland’s 2026 law changes the size, setback, density and parking framework local governments must follow. Confirm the current ordinance, overlay status and parcel-specific approvals with the Town before spending money on design or construction.
What to do next
First confirm whether your parcel is inside Preston’s Village Overlay and whether the 50% ADU cap has been amended.
- Confirm who reviews the property.
- Ask Preston for the current ADU ordinance and overlay map/status.
- Gather your zoning district, survey and utility information.
- Continue to the Maryland ADU planning tools.
Planning guidance is not permit approval.