ADU Rules in Philadelphia, PA (2026)

Philadelphia, PA permits accessory dwelling units (ADUs) on residential properties. ADUs — also called granny flats, in-law units, backyard cottages, or secondary suites — are secondary housing units on a single-family or multifamily lot. State and local law governs the approval process. In Philadelphia, the Department of Licenses and Inspections (L&I) handles ADU permit applications. Below you will find the current size limits, setbacks, fees, and timeline for building an ADU in Philadelphia.

ADU Size Limits

ADU Size Limits in Philadelphia: Detached ADU: up to 800 sq ft (max height: 24 feet). Attached ADU: Up to 40% of primary dwelling floor area. Philadelphia Code Title 14-600 series. Accessory dwelling units (referred to as 'accessory residential units' or ARUs in Philadelphia code) limited to 800 sqft detached or 40% of primary unit floor area for attached. Philadelphia does not use the California JADU concept.

Permit Fees

ADU Permit Fees in Philadelphia: Plan check fee: $300–$1,200. Building permit fee: $500–$3,000 based on construction value. Impact fees: None. School fees: None or N/A. Total estimated permit cost: $1,000–$5,000 total fees. Philadelphia does not impose development impact fees or school fees at the local level. L&I permit fees are based on construction valuation. Philadelphia Water Department (PWD) stormwater management fees may apply for impervious surface changes. Water/sewer connection fees for new ADU unit.

Permit Timeline

Philadelphia ADU Permit Timeline: Philadelphia L&I (Licenses and Inspections) issues permits. Zoning permit first, then building permit. Philadelphia eCLIPSE permit system is online. Typical timeline: 4-8 weeks for zoning approval, 2-4 weeks additional for building permit. Complex projects may require Zoning Board of Adjustment (ZBA) variance. Apply through the Department of Licenses and Inspections (L&I) online permit portal. Phone: (215) 686-2400.

Setback Requirements

ADU Setback Requirements in Philadelphia: Front setback: follows zone standard. Side setback: 4 feet. Rear setback: 12 feet. Philadelphia Code Title 14-601 et seq. Rear setback of 12 ft required for detached accessory residential units. Interior lots in RSA zones typically have shared party walls — side setback applies to corner lots. Rowhouse rear yards often 15-20 ft deep — ADU feasibility depends on yard depth. Corner lots have additional street-facing setback requirements.

Parking Requirements

Parking Requirements: No minimum parking required for accessory residential units. Philadelphia is a walkable, transit-rich city — L&I does not require additional parking for ADUs. SEPTA rail, subway (Broad Street Line, Market-Frankford Line), and extensive bus network reduce car dependency.

Restrictions & Requirements

• •Accessory residential unit must be on same lot as primary dwelling
• •Maximum one accessory residential unit per lot in RSA/RSD zones
• •ADU must comply with Philadelphia Construction Code (International Residential Code as amended)
• •Rear yard minimum 30% of lot depth must remain as open space
• •Rowhouse party walls cannot be breached without structural engineering certification
• •Historic district properties require Historical Commission review before any exterior changes
• •Unit cannot be separately conveyed (sold) apart from primary lot

How Many ADUs Are Allowed?

Number of ADUs Allowed in Philadelphia: Single-family lots: 1. Multifamily properties: Per RM zone density allowances in Title 14. Philadelphia allows one accessory residential unit per single-family lot in RSA and RSD zones. RM zones allow multiple units per base density allowances. Philadelphia is exploring expanded ADU provisions through Philadelphia 2035 Housing Element updates.

Historic District Considerations

Frequently Asked Questions