If you live on the Main Line and want space for a parent, a caregiver, or a long-term tenant, an accessory dwelling unit can be a smart, flexible solution. In Lower Merion, ADUs are defined and regulated by the township’s zoning code. What is allowed depends on your lot’s zoning district, site constraints, and any historic or neighborhood rules. This guide walks you through what counts as an ADU, where they may be permitted, and how to move from idea to approval with fewer surprises.
ADUs in Lower Merion overview
An accessory dwelling unit is a smaller, independent home on the same lot as the main house. It may be attached or detached, and it has its own kitchen and living area. Lower Merion’s code includes a formal definition of an ADU and outlines how these units are treated in its zoning framework in the township’s code.
Why this matters on the Main Line:
- Aging in place: create a safe suite for a parent or caregiver.
- Life transitions: give adult children or boomerang grads a landing spot.
- Long-term rental: add steady income while preserving privacy.
- Resale appeal: a permitted, well-designed second unit can widen your buyer pool when you sell.
The bottom line: ADUs are possible in Lower Merion, but the rules are specific. Feasibility is parcel by parcel. You will need to confirm your zoning district and the exact standards that apply before planning.
ADU types and common use cases
Attached, detached, and conversions
- Attached ADU: a new wing or over-garage suite connected to your home. This can work well when your lot has tighter setbacks.
- Detached ADU: a backyard cottage or a converted detached garage. Detached units must meet accessory building rules and sometimes principal setbacks for certain ADU pathways as outlined in the code’s ADU provisions.
- Interior conversion: a basement or third-floor apartment with its own kitchen. These are common for multigenerational living.
Match the form to your goals, your lot, and parking capacity. If you plan a detached cottage, double-check accessory structure height, setbacks, and lot coverage limits in your zoning district’s dimensional tables in Chapter 155.
Junior units and accessory apartments
Smaller units carved out of existing space, like a lock-off suite over a garage or a partial basement conversion, can be less expensive than a ground-up cottage. They must still meet building and fire code standards for habitable space and egress and must comply with zoning definitions for a separate dwelling unit see the township’s definition section.
Multigenerational living and rentals
ADUs shine for family needs. They let you keep loved ones close with independence and privacy. They can also function as a long-term rental if zoning and licensing requirements are met. Lower Merion regulates some ADUs as “restricted accessory dwelling units,” which have conditions like relationship or age limits, recorded agreements, and annual permits in specific districts. Read the requirements carefully before you plan a rental strategy in the restricted ADU section.
Where ADUs are allowed in Lower Merion
Zoning districts and overlays
ADU rules depend on your parcel’s zoning district. Lower Merion’s code includes a defined ADU use and a dedicated pathway for “restricted accessory dwelling units” in certain districts such as LDR, MDR, IC, and IH. Those conversions come with conditions that can include occupancy relationships or elderly focus, a recorded agreement, and an annual permit. In some cases, an accessory building used as an ADU must meet principal building setbacks see the restricted ADU provisions.
Because interpretations can vary by district and project type, start by confirming your parcel’s zoning using the township’s interactive lookup. Then review the district tables and supplemental use rules to see which standards apply to your lot use the parcel lookup and the zoning code resources.
Historic areas and HOAs
Many homes in Merion Station and nearby neighborhoods appear on the Historic Resource Inventory or lie within local historic districts. Exterior changes, including new detached structures or visible additions, may need Historical Commission or HARB review and a Certificate of Appropriateness. Expect design guidelines and review meetings to shape materials, massing, and placement see Historic Commission guidance.
If your property is in an HOA, review covenants for accessory structures and second units. Private rules can be stricter than township zoning.
Lot characteristics that influence feasibility
Even when zoning allows an ADU, your lot must fit the rules. Pay attention to:
- Lot width and depth for setbacks and separation
- Slope and topography that affect access and egress
- Easements and utility routes
- Driveway layout and where extra parking can fit
- Existing impervious surface totals versus district limits
Dimensional standards and coverage caps are specific to each district. Use the tables in Chapter 155 to evaluate your site early district dimensional tables.
What’s allowed: size, design, and use rules
Size, height, setbacks, and parking
- Size and height: Accessory structures often have height caps and footprint limits. ADUs within accessory buildings may need to meet the same setbacks as a principal building in some cases see ADU provisions. Confirm exact numbers in your district table here.
- Parking: The township counts ADUs as additional dwelling units for minimum parking. For example, single-family in LDR is generally 2 spaces per home plus 1 space per ADU. Plan space on-site and show compliance with the parking table in your permit application parking standards.
- Impervious surface: Many districts cap impervious coverage. New pads, walkways, or driveways can push you over the limit. You will likely need to submit an impervious calculation with your zoning application see general zoning resources and forms.
Design compatibility and privacy
While the code focuses on use and dimensions, good design helps approvals. Aim to:
- Echo the main home’s roof pitch, materials, and window style
- Orient doors and windows to reduce direct views into neighbors’ yards
- Use fencing, planting, and lighting that respects privacy
Historic or HARB review will also look at scale, massing, and visibility from the street historic review information.
Occupancy, rental durations, and licensing
- Occupancy limits: The “restricted accessory dwelling unit” path includes relationship or elderly occupancy conditions, a recorded agreement, and an annual permit. It can expire if conditions change restricted ADU section.
- Owner occupancy and sponsors: Some restricted pathways imply owner occupancy or allow nonprofit sponsorship if not owner-occupied. Clarify this with the Zoning Officer for your specific case code reference.
- Rental licensing: If you rent an ADU, you must get a Rental Unit License and pass inspections. Licenses are renewed annually rental licenses.
Permits and approvals in Lower Merion
Zoning verification and pre-application
- Look up your parcel’s zoning and overlays with the township’s map tool parcel lookup.
- Read the definition and district rules that apply to your property definitions and district tables.
- Review the restricted ADU section to understand conditions, recorded agreements, and permit renewal requirements restricted ADU provisions.
- Email or meet with the Zoning Officer for a pre-application check. Bring a simple sketch showing the proposed unit, setbacks, parking, and estimated impervious totals zoning department info.
Building permits, plans, and inspections
All habitable ADUs require building permits and must meet building, fire, and life safety standards. Expect to provide:
- Site plan with dimensions, setbacks, and parking
- Architectural plans showing layout, egress windows and doors, fire separation, and mechanical systems
- Impervious coverage worksheet
- Contractor licenses and insurance
Use the township’s online permitting portal to submit and track applications. Inspections will occur at key stages before final approval online permitting portal and building code references within ADU section.
Timelines, fees, variances, and appeals
Most compliant ADUs are reviewed administratively. If your plan conflicts with a setback, height, or coverage limit, you may need relief through the Zoning Hearing Board. Build time into your schedule and weigh design tweaks that avoid variances. The township’s new zoning code and updates can affect timing, so verify current processes before you apply zoning code overview.
Costs, ROI, and property search strategy
Cost drivers and financing options
Budget drivers include whether the ADU is attached or detached, foundation work, utility upgrades, parking, and any stormwater measures for new impervious area. Many owners explore renovation loans or a HELOC. Talk with your lender early so your financing fits township timelines and inspections.
Appraisal, resale, and insurance
A legally permitted and well-documented ADU can support value by adding livable space and flexibility. Appraisers will look for permits and quality. Keep records of approvals, plans, and final inspections. Update your insurance to reflect the added unit and any rental use.
Finding ADU-ready homes on the Main Line
If you are shopping with an ADU in mind, prioritize:
- Lots with depth and rear access for a detached unit
- Existing detached garages suitable for conversion
- Walkout basements for lower-cost interior apartments
- Driveway layouts that allow an extra parking space on-site
- Properties outside strict historic visibility zones, or with limited street exposure
Start with a zoning check for each promising address. The township’s map and code are your best tools for screening listings quickly parcel lookup and definitions and standards.
Next steps for your ADU plan
- Confirm your parcel’s zoning and overlays with the township map.
- Sketch a simple concept with location, size, and parking.
- Review the ADU definition, district tables, parking standards, and restricted ADU conditions so you know the rules that apply to your lot definitions, district tables, parking, and restricted ADUs.
- Book a pre-application conversation with the Zoning Officer to validate feasibility and next steps zoning contacts.
- Line up your lender and contractor, then prepare permit-ready plans using the online portal permit portal.
If you want help evaluating ADU potential for your home or targeting listings with the right lot, setbacks, and parking, reach out. I will help you coordinate zoning checks, compare options, and plan your return on investment. Start with a conversation and a value snapshot. Connect with Cathy McClatchy to Get a Free Home Valuation and a tailored ADU feasibility review for your address.
FAQs
Are ADUs legal in Lower Merion?
- Yes, ADUs are defined in the zoning code. Certain “restricted accessory dwelling units” are allowed with specific conditions in listed districts. Always verify your parcel’s district and the standards that apply ADU definition and restricted ADUs.
Which districts allow restricted ADU conversions?
- The code identifies districts such as LDR, MDR, IC, and IH for restricted ADUs, subject to conditions like recorded agreements, occupancy limits, and annual permits. Read the code text to confirm details for your case restricted ADU provisions.
How do I check if my property is eligible?
- Use the township’s parcel lookup to confirm zoning, then read the applicable district tables and ADU provisions. Follow up with the Zoning Officer for written clarification parcel lookup and district tables.
Can I build a detached backyard cottage?
- Possibly. You must meet accessory structure height and setbacks, parking additions, and coverage limits. Some ADU paths require the accessory building to meet principal setbacks. Confirm specifics in the code and with staff ADU rules and district standards.
Do I need extra parking for an ADU?
- Yes. ADUs count toward minimum parking. For example, in LDR single-family, plan for 2 spaces for the main home plus 1 additional space for the ADU parking standards.
Are there special rules for historic properties?
- Yes. Properties in historic districts or on the Historic Resource Inventory may need Historical Commission or HARB review for exterior changes and visible structures historic review.
What permits will I need?
- Expect a zoning permit and a building permit. If the ADU will be rented, you also need a Rental Unit License with inspections. Use the online portal to submit applications permit portal and rental licensing.
Do I have to live on-site to have an ADU?
- The restricted ADU pathway includes occupancy and sometimes owner- or sponsor-related conditions. Confirm the exact requirement for your property and ADU type with the Zoning Officer restricted ADUs.
How long does approval take?
- Timelines vary by scope and completeness of plans. Straightforward projects with compliant designs can move faster. Projects needing variances or historic review take longer. Check current processes with the Building and Planning Department zoning code overview.
