ADU rules in Philadelphia, PA — also called accessory dwelling unit regulations or granny flat ordinances — cover setbacks, owner-occupancy, parking, and permit requirements.
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.
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. The city's L&I Accessory Dwelling Unit Checklist (PZ_004) confirms the gatekeeping requirements: the property must be in the RSA-5 or CMX-1 base zoning district (or qualifying overlay), the lot area must be at least 1,600 sq. ft. 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. No more than one ADU is allowed per lot, the floor area may not exceed 800 sq. ft. (unless the ADU is within a qualifying historic structure under 14-604(11)(d)(.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.
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.
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