Thinking about adding a backyard cottage or finishing a basement suite in Silver Spring? An accessory dwelling unit can create space for multigenerational living or a steady rental stream, but the rules and process can feel overwhelming at first. You want clarity on what is allowed, how to get permits, and what to expect with taxes, parking, and utilities. This guide breaks down the essentials for Montgomery County so you can plan with confidence and avoid costly missteps. Let’s dive in.

What counts as an ADU

An accessory dwelling unit, often called an accessory apartment, is a smaller, independent home on the same lot as a primary residence. You will see three common types in Silver Spring.

• Interior ADU: A conversion within your existing home, like a basement apartment or attic suite, with its own kitchen, bath, and entrance.
• Attached ADU: A new or expanded wing that shares a wall or foundation with the main house but functions as a separate dwelling.
• Detached ADU: A stand-alone structure, such as a garage conversion or backyard cottage, that is secondary to the main home.

ADUs remain accessory to a single-family home and are not the same as building multiple principal dwellings. They must meet zoning and building standards set by Montgomery County.

Where ADUs are allowed

Silver Spring sits in unincorporated Montgomery County, so county zoning and permitting rules apply. ADUs are commonly permitted in residential zones, subject to size, coverage, height, and setback standards. Special zones and overlays can add rules, and properties in local historic districts may need design review before you build.

Most places allow one ADU per single-family lot, but details vary and can change. Start by checking your parcel’s zoning designation and any overlays. If your neighborhood has a homeowners association, review covenants because HOA rules can be more restrictive than county zoning.

Ownership and leasing basics

Some jurisdictions require an owner to live on the property in either the main home or the ADU. Confirm whether Montgomery County currently requires owner-occupancy before you move forward. Long-term leasing is commonly allowed when you meet licensing and safety requirements.

Short-term rentals, like nightly stays, follow a different set of county rules and may require registration, occupancy limits, and taxes. Plan early so your design and safety features align with how you intend to use the unit.

Parking, access, and design

Parking is a frequent concern. Many communities require at least one off-street space for an ADU, with possible reductions near strong transit. Silver Spring’s Metro and bus access can influence whether parking minimums apply to a specific site, so review county parking standards for your address.

Detached ADUs usually follow accessory structure height limits and side or rear yard setbacks. Attached units must meet principal building setbacks and height rules. If you are in a historic district, expect design review and compatibility requirements.

Building codes and utilities

All ADUs must meet building, fire, electrical, plumbing, and mechanical codes. You will need building and trade permits, inspections during construction, and a final occupancy approval before anyone moves in or you start renting. Safety items like smoke alarms, carbon monoxide detectors, proper egress, and fire separation walls are mandatory.

Utility planning is critical. Some ADUs share existing service lines, while others need separate meters or upgraded systems. Coordinate early with the Washington Suburban Sanitary Commission for water and sewer requirements. If the property uses a septic system, confirm capacity with the county health department.

Permitting steps and timelines

Montgomery County’s process typically includes application submittal, plan review, corrections, permit issuance, inspections, and a final occupancy certificate. Timelines depend on the quality of your plans, the complexity of your project, and whether historic review applies. Fees include plan review and permit fees, inspections, and any water or sewer connection charges.

A brief consultation with the Department of Permitting Services or a knowledgeable design professional can save time. Clear plans that address zoning, parking, setbacks, and utilities from the start usually move faster.

Costs, financing, taxes, and insurance

Budgets vary widely based on scope. Interior conversions are often the most cost-efficient. Detached cottages and garage rebuilds tend to be higher cost due to site work and utilities. Get multiple local contractor estimates and factor in permit and connection fees.

Owners often fund ADUs with cash, a home equity line of credit, a cash-out refinance, or a renovation loan. Lender policies can differ by unit type and rental plans, so check terms early. Adding finished living space can increase your assessed value and may change your property taxes. Rental income is taxable, and you may need a rental license depending on how you lease the unit. Notify your insurer, since ADUs can affect liability coverage and premiums.

Step-by-step checklist for Silver Spring

• Step 1: Confirm your zoning and whether you are in a historic district; identify any overlays that apply to the property.
• Step 2: Speak with Montgomery County Planning or the Department of Permitting Services to understand current ADU standards and submittal requirements.
• Step 3: Review HOA covenants, deed restrictions, and your mortgage terms for any limits on ADUs or rentals.
• Step 4: Contact the Washington Suburban Sanitary Commission about water and sewer capacity and connections; if on septic, coordinate with the county health department.
• Step 5: Hire an architect or designer to prepare code-compliant plans that address size, setbacks, parking, and lot coverage.
• Step 6: Submit zoning verification if needed, then file building and trade permit applications with Montgomery County DPS.
• Step 7: Pull permits, schedule inspections at required milestones, and secure the final occupancy approval before anyone moves in.
• Step 8: Update your insurer and tax records, and obtain any required local rental or business licenses before advertising the unit.

Common pitfalls to avoid

• Skipping a zoning check before design. If your plan does not meet standards, you may face delays or redesign costs.
• Overlooking HOA covenants or private deed restrictions that can prohibit ADUs even when zoning allows them.
• Underestimating water, sewer, or septic capacity. Utility constraints can drive cost or prevent approval.
• Renting before you have a final occupancy certificate. That can result in fines and required corrections.
• Assuming any lender will finance the project. Some lenders have limits related to accessory units or rentals.

How ADUs affect buying or selling

If you plan to sell, a well-designed ADU can broaden your buyer pool and create a compelling value story. Buyers often appreciate flexible space for family or future rental income, provided the unit is permitted and compliant. Clear documentation, a certificate of occupancy, and rental license records help maximize confidence.

If you are buying with the goal of adding an ADU, due diligence matters. Verify zoning, check for historic review, confirm utility capacity, and read HOA covenants. If a home already has an ADU, ask for permits, inspections, and occupancy approvals so you know the unit is legal and safe.

Ready to plan your ADU strategy?

Whether you are creating long-term housing for family or building a rental to offset your mortgage, an ADU can be a smart play with the right plan. Our team can connect you with local designers, contractors, and lenders who understand Montgomery County rules and timelines, and we can help you position the project for future resale value. Reach out to the Dana Rice Group to request a complimentary market plan and staging consultation.

FAQs

What is an ADU in Montgomery County?

• An accessory dwelling unit is a smaller, independent home on the same lot as a primary residence and can be interior, attached, or detached, subject to county zoning and building codes.

Can I build an ADU on a small Silver Spring lot?

• It depends on your zoning, setbacks, height limits, lot coverage, and any overlays or historic rules; confirm standards for your parcel before you design.

Do I have to live on-site to rent an ADU in Silver Spring?

• Some places require owner-occupancy, so check Montgomery County’s current rule before planning your lease or marketing the unit.

Are short-term rentals allowed for ADUs in Silver Spring?

• Short-term rentals follow separate county regulations that can include registration, occupancy limits, safety requirements, and taxes; verify before listing.

How much does an ADU cost and how long will it take?

• Costs vary by scope, from interior conversions to detached builds, and timelines depend on design complexity and permit reviews; get local estimates and confirm DPS timeframes.

Will an ADU change my property taxes in Montgomery County?

• Adding living space can increase your assessed value and property taxes; consult county assessment procedures to understand the impact.

Who handles water and sewer for ADUs in Silver Spring?

• The Washington Suburban Sanitary Commission oversees water and sewer connections and capacity; contact them early to avoid utility delays.