ADU Rules in Philadelphia, Pennsylvania

Philadelphia is Pennsylvania's largest city and the only First Class City in the Commonwealth, governed under the Philadelphia Home Rule Charter rather than standard state municipal law. With approximately 1.5 million residents and a built environment dominated by historic rowhouses, the ADU landscape here differs fundamentally from most other cities in the country.

No Pennsylvania Statewide ADU Law

Pennsylvania has not enacted statewide ADU preemption legislation. Unlike California or Oregon, Pennsylvania leaves ADU regulation entirely to local municipalities under the Pennsylvania Municipalities Planning Code (MPC). Philadelphia, as a Home Rule city, has even broader local authority. All ADU rules in Philadelphia are governed by the Philadelphia Zoning Code.

Philadelphia's Rowhouse Context

The vast majority of Philadelphia's residential neighborhoods consist of attached rowhouses — properties that share party walls on both sides with no side yards and minimal rear yards. This physical reality means:

• Detached ADUs (backyard cottages) are rarely feasible in most of the city's residential fabric.
• Accessory apartments within existing structures are the practical ADU form: basement units, upper-floor conversions, converted rear additions, and garage/carriage house adaptations.
• Some neighborhoods in Northwest Philadelphia, Chestnut Hill, and the far Northeast have detached single-family homes where detached accessory structures may be more viable.

Philadelphia Zoning Code Framework

Philadelphia's Zoning Code (adopted 2012, frequently amended) uses a tiered district system:

• RSA-5: The most common rowhouse residential district. Single-family use is the primary permitted use. Conversion to a two-unit or accessory apartment requires careful review and may need a variance from the Zoning Board of Adjustment (ZBA).
• RSA-3, RSD-1, RSD-3: Lower-density districts where detached accessory structures may be more feasible but require conformance with setback and lot coverage rules.
• RM-1, RM-2, RM-4: Multi-family residential districts where accessory dwelling arrangements are more commonly permitted.
• RMX-1, RMX-2: Residential mixed-use districts with more flexibility for additional units.

Setbacks, Lot Coverage, and Size

Specific setbacks and maximum lot coverage vary by zoning district. In dense RSA-5 rowhouse districts, rear yard depth requirements and lot coverage maximums may limit accessory structure construction. Any accessory structure generally must:

• Be subordinate in size and function to the primary dwelling.
• Comply with the applicable district's setback minimums (front, rear, and side where applicable).
• Meet the Philadelphia Building Code (based on International Building Code) for habitability, including egress windows, ventilation, and minimum ceiling heights.

Permit Process

All accessory dwelling work requires:

1. Zoning permit — reviewed by the Philadelphia Department of Licenses and Inspections (L&I). Submit via eCLIPSE (eclipsepermits.phila.gov).
2. Building permit — required for structural work, new construction, or change of occupancy.
3. Zoning Board of Adjustment (ZBA) — if the proposed use is not permitted as-of-right, you must apply for a variance or special exception.

The Philadelphia City Planning Commission provides guidance on zoning interpretations and may be involved in larger development reviews.

Historic Districts

Philadelphia has extensive historic districts (Old City, Society Hill, Germantown, Chestnut Hill, and many others) overseen by the Philadelphia Historical Commission. Any exterior work on a historically designated building or in a historic district requires a Certificate of Appropriateness before permits are issued.

Contact

• Department of Licenses and Inspections: (215) 686-2400, eCLIPSE online portal
• Zoning Board of Adjustment: (215) 686-2429
• Philadelphia City Planning Commission: (215) 683-4615, phila.gov/departments/city-planning

Disclaimer: Zoning regulations change frequently. Verify all information directly with the Philadelphia Department of Licenses and Inspections and the Philadelphia Zoning Code before making any development decisions.