Philadelphia, PA Accessory Structures: ADU Rules (2026)
ADU rules in Philadelphia, PA, also called accessory dwelling unit regulations or granny flat ordinances, cover setbacks, owner-occupancy, parking, and permit requirements.
Key Facts
- Code Section
- Philadelphia Zoning Code Sec. 14-604(11)
- Permitted Districts
- RSA-5 or CMX-1 base district (plus qualifying overlays)
- Max Floor Area
- 800 sq. ft. (more allowed only in qualifying historic structures)
- Location
- Inside principal building or pre-existing detached accessory building (e.g. detached garage)
- Owner Occupancy
- Required; affidavit + deed restriction recorded before occupancy
- Number per Lot
- Maximum of one ADU per lot
Summary
Philadelphia permits accessory dwelling units (ADUs) only on lots in the RSA-5 or CMX-1 base zoning districts (and certain overlay districts), under Zoning Code Section 14-604(11). The ADU must be inside the principal building or inside a detached accessory building (such as a detached garage) that already existed as of the Code's effective date, be no larger than 800 square feet, be limited to one per lot, and the owner must occupy either the principal or accessory unit.
Location: ADUs must be located within the principal building or within a detached accessory building, such as detached garages, that are in existence as of the effective date of this Zoning Code. Maximum of One ADU: No more than one accessory dwelling unit is allowed per lot. Floor Area of ADU: The floor area of the ADU may not exceed 800 square feet, OR the ADU is within a historic structure as described in 14-604(11)(d)(.1); therefore the floor area of the ADU is permitted to exceed 800 square feet. Owner Occupied: The principal dwelling unit or the ADU must be occupied by the owner of the subject lot, AND Before final occupancy of the accessory dwelling unit, the property owner shall record an affidavit and deed restriction, stating that the property owner will reside on the property, in either the principal or ADU. Number of Entrances: Only one entrance to a building containing an accessory dwelling unit may be located on the front facade that faces a street unless the building contained an additional street-facing entrance before the ADU was created.
Full Breakdown
Under Section 14-604(11) of the Philadelphia Zoning Code, an accessory dwelling unit is allowed only on a lot occupied by a single-family use in a detached or semi-detached building in the permitted areas, except that within a historic structure an ADU is also permitted on a lot occupied by a single-family use in an attached building. with no more than one dwelling unit otherwise permitted, and the principal structure must be semi-detached or detached (per 14-203(46) and 14-203(47)). The ADU must be located within the principal building or within a detached accessory building, such as detached garages, that are in existence as of the effective date of the Zoning Code - new detached ADU structures are not permitted by-right.
1)), and only one street-facing entrance is allowed unless an extra one pre-existed. The owner must occupy the principal unit or the ADU, and before final occupancy must record an affidavit and deed restriction confirming continued residence. Pennsylvania has no statewide ADU mandate - the Municipalities Planning Code (Act 247 of 1968) delegates this entirely to local zoning - so Philadelphia's Section 14-604(11) controls.
Violations & Fines
Creating or occupying an ADU without a zoning/use registration permit, or in a district where it is not permitted, is a Zoning Code violation enforced by the Department of Licenses and Inspections; a refusal triggers an appeal to the Zoning Board of Adjustment requiring a community meeting and public hearing. Failure to record the required owner-occupancy affidavit and deed restriction blocks final occupancy approval.
Frequently Asked Questions
Can I build a brand-new backyard ADU cottage in Philadelphia?
Which zoning districts allow ADUs in Philadelphia?
How big can a Philadelphia ADU be?
Do I have to live on the property?
Sources & Official References
Other rules in Philadelphia
How Philadelphia compares: Easiest Cities to Build an ADU·Compare Philadelphia to another location·View the Pennsylvania accessory structures overview
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