ADU rules in Philadelphia

A backyard ADU is possible only as a conversion of a detached building that is already there. Section 14-604(11)(c) requires the unit to sit inside the principal building or inside a detached accessory building such as a garage that was in existence when the Zoning Code took effect on August 22, 2012, so building a new backyard cottage is not an option. The lot must also fall into one of the two permitted areas in 14-604(11)(d): a building designated historic (or a contributing building in a historic district), or a lot of at least 1,600 sq. ft. in the RSA-5 or CMX-1 district on which no more than one dwelling unit is otherwise permitted. Outside historic structures the house must be in a detached or semi-detached building, so most Philadelphia rowhouse lots do not qualify. Seven overlay districts strip the right entirely or partly, including /SIX, which bans ADUs across all of Council District 6.

An interior conversion (basement, attic, or a floor of the house) is the main way a Philadelphia ADU gets built, and it passes through the same two gates as a garage conversion: a designated historic structure or contributing building anywhere in the city, or a lot of at least 1,600 sq. ft. in RSA-5 or CMX-1 where only one dwelling unit is otherwise permitted. Section 14-604(11)(c) allows the principal building to be an attached rowhouse only within historic structures; everywhere else the house must be detached or semi-detached. The unit must be within the interior of the principal building, so an addition built specifically to hold the ADU is not the permitted form. Only one entrance to the building may face the street unless a second street-facing entrance existed before the ADU was created, per 14-604(11)(h).

Section 14-604(11)(i) caps the floor area of an accessory dwelling unit at 800 sq. ft., 'except in historic structures' as described in subsection (d)(.1), so an ADU inside a designated historic building or a contributing building in a historic district has no square-foot ceiling and is limited instead by the general accessory-use rule that it stay subordinate in area and function to the principal dwelling (14-604(1)(c)(.1)). Only one accessory dwelling unit is allowed per lot (14-604(11)(f)), and no extra land area is required beyond the district's minimum lot size (14-604(11)(g)). Both the 800 sq. ft. figure and the historic-structure exception come from Bill No. 190612, approved November 6, 2019 and effective January 1, 2020. On the RSA-5 and CMX-1 path the lot itself must be at least 1,600 sq. ft.

The owner has to live on the property, in either the main house or the ADU, and it is an ongoing obligation rather than a one-time check at application. Section 14-604(11)(e) requires the owner to record an affidavit and deed restriction stating that they will reside on the property before the accessory dwelling unit can receive final occupancy, and once recorded that deed restriction may not be removed or modified without Zoning Board of Adjustment approval. Pennsylvania has no statewide ADU statute preempting local owner-occupancy rules, so the local text controls in full. In practice this means only one of the two units on the lot can be rented out at any time.

Section 14-604(11) imposes no parking requirement of its own and 14-604(11)(g) says no additional land area is required, so parking falls back on the base district ratios in Chapter 14-800. Table 14-802-1 requires 0 spaces for single-family and two-family household living in the RSA-4/5/6, RTA-2 and RM-1 column, so an ADU taken through the RSA-5 route adds no parking obligation. CMX-1 is deliberately excluded from the commercial table: under 14-802(7)(a) a CMX-1 building must meet the parking requirements of the most restrictive adjacent district, so a CMX-1 lot next to RSD-1/2/3, RSA-1/2/3, RTA-1 or RMX-1 (where single-family is 1 space per unit) can be pulled up to one space. A historic-structure ADU sits in whatever district the building occupies, so check that district's row before assuming zero.

An accessory dwelling unit that meets every standard of 14-604(11) is allowed by right, with no discretionary hearing. Section 14-604(1)(a) permits accessory uses in conjunction with allowed principal uses unless the Code expressly says otherwise, and L&I issues the zoning and use registration permits administratively under 14-303(6), approving an application if it complies with the Code. A proposal that misses any standard has no conditional-use path in Philadelphia: the only route is a variance (or, for uses marked S in the use tables, a special exception) from the Zoning Board of Adjustment. Two extra reviews attach in practice: the Historical Commission reviews work on designated historic buildings under Chapter 14-1000, and later removal of the recorded owner-occupancy deed restriction requires Zoning Board approval.

Nothing in 14-604(11) bars renting an accessory dwelling unit, but the recorded owner-occupancy deed restriction means the owner must occupy one of the two units, so only one of them can be a conventional rental. Renting that unit for more than 30 days requires a Rental License under Code section 9-3902(1)(a); 9-3902(1)(b)(.2) exempts a unit occupied by the owner or a member of the owner's family, subject to an Affidavit of Non-Rental. Stays of 30 consecutive days or less are 'limited lodging' under 14-604(13), which may only be conducted by the dwelling unit's primary resident (an owner entitled to the homestead exclusion, or a renter living there more than half the year with the owner's written authorization), requires a Limited Lodging Operator License under 9-3909 plus a zoning permit and a licensed booking agent, and caps the unit at three unrelated occupants with no separate street-facing entrance for the lodging. In the Tenth Councilmanic District only an owner who is the primary resident may hold that license. Bill No. 260241, approved June 23, 2026 and effective August 22, 2026, adds landlord lease disclosure and neighbor notification duties to this regime.