Last researched: September 19, 2026. The Town of Somerset has one of the more detailed municipal ADU permit frameworks in Montgomery County. The Town Code expressly defines accessory dwelling units, requires a Town ADU permit for new units and conversions, applies its own accessory-building setback formulas, and currently requires at least one on-site parking space for an ADU.
Homeowner takeaway: A Somerset ADU is a two-layer project. Montgomery County controls the underlying zoning/use and issues applicable County permits, while the Town of Somerset separately reviews its own building, setback, parking, stormwater, tree and related requirements. A County approval does not by itself complete the Town process.
Town of Somerset ADU planning snapshot
| Question | What we verified |
|---|---|
| Town ADU permit required? | Yes. No ADU may be erected, replaced, converted or renovated without a Town permit. |
| County permit also required? | Yes when Montgomery County requires one; the Town permit cannot be issued until the County permit for the identical work is provided. |
| Approval level | The current Town permit application identifies ADU permits as requiring Town Council approval. |
| ADU definition | A second dwelling unit located within a main building or an accessory building; a detached ADU is a dwelling unit that is a detached accessory building or part of one. |
| Interior-lot rear-yard coverage | Accessory building may not occupy more than 25% of the rear yard. |
| Front-lot-line setback | Interior-lot accessory building must be at least 60 ft from the front lot line. |
| Base side/rear setback | 5 ft for an accessory building 10 ft high or less, with larger setbacks as height and length increase. |
| Accessory-building height | 25 ft to highest roof point and 20 ft to mean roof height for specified pitched roofs. |
| ADU parking | Current Town Code requires at least one on-site parking space; existing driveway/garage parking can satisfy it if at least three spaces exist on the property. |
| 2026 parking-study issue | The Town Council discussed whether to conduct a special ADU parking study at an April 20, 2026 work session. |
| Landlord license | If applicable, the Montgomery County landlord license for the ADU must be provided before final Town inspection approval. |
Somerset requires a separate Town ADU permit
Town Code § 112-3 expressly says no accessory dwelling unit may be erected or replaced, and no existing structure may be modified, converted or renovated into an ADU, without first obtaining a permit from the Town of Somerset.
The Town’s current permit application separately lists an Accessory Dwelling Unit Permit for:
- erection or replacement of a new structure into an ADU; and
- modification, conversion or renovation of an existing structure into an ADU.
The same application identifies the ADU permit as requiring Town Council approval, not merely administrative sign-off.
Montgomery County approval still matters
Somerset’s Town permit does not replace Montgomery County approval. The Town Code says that before a Town permit is issued, the applicant must provide the applicable Montgomery County permit for the identical work.
The Town Council can consider or approve a Town application before the County permit is physically in hand, but the Town permit itself cannot be issued until the County permit is provided.
For an ADU, think of the process as two coordinated tracks:
- Montgomery County: underlying zoning/use, County building and applicable trade permits; and
- Town of Somerset: Town ADU/building permit, Town setbacks, parking, lot coverage, stormwater, trees and other local requirements.
Somerset’s Town Code defines both attached/internal and detached ADUs
The current Town Code defines an accessory dwelling unit as a second dwelling unit that is an accessory use and is located within a main building or an accessory building.
It separately defines a detached accessory dwelling unit as a dwelling unit that is a detached accessory building or part of one.
A dwelling unit must provide complete living facilities for one household, including at least cooking, sanitation and sleeping facilities.
The base accessory-building setback starts at 5 ft
Somerset does not use a single fixed setback for every accessory building. On an interior lot, the base side/rear setback depends on building height.
For accessory buildings:
- 10 ft high or less: 5-ft minimum setback;
- over 10 ft but under 15 ft: 5 ft plus 1 additional foot of setback for every foot or fraction of a foot above 10 ft;
- 15 ft or more: 10 ft plus 2 additional feet for every foot or fraction of a foot above 15 ft.
This means a taller detached ADU can require materially more distance from the side and rear lot lines than the 5-ft starting point.
Long accessory buildings need additional setback too
Somerset also increases the setback based on the linear dimension of the accessory building:
- 24 ft or less: 5-ft base setback;
- over 24 ft: add 1 ft of setback for every foot or fraction of a foot above 24 ft.
If the building is both taller than 10 ft and longer than 24 ft, the Town adds the height-based and length-based increases together.
The Town Code gives an example: a 15-ft-high accessory building with a 30-ft dimension would require a 16-ft setback under the formula.
For a detached ADU, footprint shape can therefore matter almost as much as total square footage.
Interior-lot accessory buildings also have rear-yard and front-line limits
On an interior lot, the accessory building:
- must be located in the rear yard;
- may not occupy more than 25% of the rear yard; and
- must be at least 60 ft from the front lot line.
A detached ADU can therefore satisfy the side/rear setback formula but still fail because of rear-yard coverage or front-lot-line distance.
Some Somerset lots use Montgomery County accessory-building setbacks
Somerset’s setback section contains exceptions where Montgomery County accessory-building setback provisions apply instead of the Town’s standard interior-lot formula.
One listed category is a lot with less than 60 ft of frontage. Corner lots also use Montgomery County setback rules, adjusted by Somerset’s height and linear-dimension formulas.
That means homeowners should not calculate a detached ADU envelope from a generic Somerset diagram without first confirming the lot category.
Accessory buildings can be up to 25 ft at the highest roof point
Somerset’s current building code says an accessory building may not exceed:
- 25 ft to the highest point of the roof surface; and
- 20 ft to the mean height between eaves and ridge for gable, hip, pyramidal, mansard or gambrel roofs.
Remember that increasing the height can also increase the required side/rear setbacks under the Town’s formula.
Somerset currently requires one on-site ADU parking space
The current Town Code says that when:
- a detached ADU is erected;
- an accessory structure is converted or renovated to contain an ADU; or
- an ADU is added to the main building;
a minimum of one on-site parking space must be provided.
Existing driveway or garage parking may satisfy the requirement if at least three parking spaces exist on the property.
The Town discussed an ADU parking study in April 2026
Maryland’s statewide law limits additional off-street parking requirements imposed specifically on ADUs. A jurisdiction generally needs the required parking study before imposing additional ADU parking and must provide a waiver process.
Somerset’s April 20, 2026 Town Council work-session agenda specifically included a discussion on “Conducting a Parking Study on a Special Parking Requirement for Accessory Dwelling Units (ADUs).”
During this September 19 research pass, I did not find a clearly posted final parking-study result or later Town ordinance removing or revising the one-space requirement.
For a current application, ask the Town whether the one-space rule remains enforceable under the final 2026 implementation and what variance or waiver procedure applies.
The Town permit application is already designed for ADUs
Somerset’s current permit materials ask the applicant to identify:
- whether the ADU is attached or detached;
- the gross floor area of the existing home;
- the proposed ADU square footage;
- the number of ADU bedrooms; and
- whether utilities will be shared or separate.
That makes the Town’s permit process more mature than municipalities that are only now drafting an ADU form.
A Montgomery County landlord license can be part of final approval
Somerset’s Code says that, where applicable, an applicant must submit a copy of the Montgomery County landlord license for the proposed ADU before approval of the final inspection.
The same requirement appears in the Town’s application-document provisions.
If your ADU will be rented, confirm the current County landlord-license requirement and whether any Town-specific rental rule also applies.
Maryland’s 75% size rule still controls the statewide framework
Somerset’s Town Code is primarily regulating the Town permit, building placement and related local requirements. Montgomery County zoning governs the underlying ADU size/use rules.
Maryland now defines an ADU as no greater than 75% of the size of the primary single-family detached dwelling, and Maryland Planning says covered jurisdictions may not impose a lower local maximum.
For a Somerset homeowner, ask both the Town and Montgomery County:
- how the primary dwelling is measured;
- what current Montgomery County ADU size rule applies after HB 1466;
- whether attached and detached ADUs use the same calculation; and
- how the County size rule interacts with Somerset’s much tighter physical building envelope.
Use our Maryland ADU size guide to understand the state framework before choosing a floor plan.
Stormwater and trees can materially change a Somerset ADU project
Somerset’s Town permit review extends beyond setbacks. The Town Code includes stormwater-management requirements, tree rules and planting-plan requirements for new construction.
A detached ADU that fits the zoning envelope can still require additional design work for:
- stormwater retention or environmental site design;
- tree protection or removal permits;
- replacement planting;
- impervious-surface limits; and
- construction-management requirements.
Include those reviews early rather than treating them as post-design paperwork.
What to ask Somerset before paying for ADU plans
- What current Montgomery County ADU zoning rule applies to my lot?
- How does Somerset calculate the Town setback for my proposed height and length?
- Does my lot fall under a Montgomery County setback exception?
- What is my rear-yard area and 25% accessory-building coverage limit?
- Does the 60-ft front-lot-line rule apply?
- Does the current one-space ADU parking requirement still apply after the 2026 parking-law changes?
- Was a Town ADU parking study completed?
- What parking variance or waiver process is available?
- Does my project require Town Council approval?
- What County permit must be obtained before the Town permit is issued?
- Will a landlord license be required?
- What stormwater, tree and impervious-surface requirements apply?
Town of Somerset homeowner checklist
- Confirm the property is inside the Town of Somerset.
- Confirm Montgomery County’s current ADU zoning/use requirements.
- Schedule the Town code-compliance meeting if required for new construction.
- Measure accessory-building height and length before calculating setbacks.
- Check whether the lot qualifies for a County-setback exception.
- Calculate rear-yard coverage and front-lot-line distance.
- Confirm the current ADU parking rule.
- Prepare County and Town permit materials.
- Address stormwater and trees early.
- If renting the unit, confirm landlord licensing.
- Do not order a prefab unit until both County zoning and the Town building envelope are confirmed.
Town of Somerset ADU FAQs
Does Somerset require its own ADU permit?
Yes. The Town Code expressly requires a Town permit for a new ADU or for converting or renovating an existing structure into an ADU.
Do I also need a Montgomery County permit?
Yes when County permitting applies. Somerset can consider the Town application first, but the Town permit cannot be issued until the applicable Montgomery County permit for the identical work is provided.
What is the setback for a detached Somerset ADU?
There is no single number for every detached ADU. The base interior-lot setback starts at 5 ft for an accessory building 10 ft high or less, then increases with building height and with any side/rear building dimension over 24 ft. Some lots use Montgomery County setback rules instead.
How tall can a Somerset accessory building be?
The Town Code allows up to 25 ft to the highest roof point and up to 20 ft to mean roof height for specified pitched roofs, subject to the other Town requirements.
Does Somerset require ADU parking?
The current Town Code requires at least one on-site ADU parking space, which can be satisfied by existing driveway or garage parking if at least three spaces exist on the property. Because the Town discussed an HB 1466-related ADU parking study in April 2026, confirm the current enforceability and waiver process before design.
Who should I contact about a Somerset ADU?
Start with the Town of Somerset Town Hall at 4510 Cumberland Avenue, Chevy Chase, Maryland 20815, and coordinate the project with Montgomery County permitting and zoning staff as required.
Primary sources checked
- Town of Somerset — Article II Town Building Permits and § 112-14 building/ADU parking rules
- Town of Somerset — Chapter 112 definitions
- Town of Somerset — 2026 Permit and Variance Application / ADU Permit
- Town of Somerset — April 20, 2026 ADU Parking Study Discussion
- Maryland Department of Planning — HB 1466 ADU FAQ
Maryland ADU Guide is an independent research publication, not the Town of Somerset, Montgomery County, M-NCPPC, a law firm, architect or contractor. This page reports the current Town ADU permit, accessory-building setback/height rules, parking provision and April 2026 parking-study discussion, while distinguishing them from Montgomery County zoning. Confirm current County zoning and Town permit requirements before spending money on design or construction.
What to do next
Confirm both Montgomery County zoning and Somerset’s Town building envelope before choosing a detached ADU plan.
- Confirm the property is inside the Town of Somerset.
- Confirm Montgomery County’s current ADU zoning and permit requirements.
- Ask Somerset to calculate the applicable height/length setback formula and current parking rule.
- Continue to the Maryland ADU planning tools.
Planning guidance is not permit approval.