Compare ADU rules across Pennsylvania

A detached ADU (an ADU inside an accessory outbuilding) is allowed only where the house is one of the four house building types, and only in that type's zones: Twin House in N3, N4, GX-C and GX-N; House A in N3 and N4 only; House B in N3, N4 and N5; House C in N5. The three rowhouse types that permit an ADU allow it only inside the principal building, and Lane Rowhouse (N1, N2), Small General Building and every commercial, mixed-use and industrial building type allow no ADU at all. Three gates then apply citywide: the lot may hold only one dwelling unit, the principal dwelling and ADU combined must total at least 1,750 square feet, and a lot with a detached ADU must have access to an alley or street abutting its rear or street-side lot line. Once those are satisfied the approval is administrative, not a hearing.

Ordinance read August 2026

An ADU inside the principal building, created either by converting existing interior floor area or by adding floor area, is allowed in more building types than a detached one: Town Rowhouse (GX-C, and GX-N/N2), Urban Rowhouse (GX-N, N1) and Suburban Rowhouse (GX-C, NX, N3) each allow '1 in principal building', and all four house types allow it in the zones listed for detached ADUs. It is still not universal. Lane Rowhouse (N1, N2) and Small General Building allow none, and House A allows none in GX-C, GX-N, NX or N2, because those columns already permit two to six principal units and § 660-42.C(1)(a) restricts ADUs to lots occupied by a single dwelling unit. The same 1,750 square foot combined-floor-area gate applies, and only one entrance to the principal building may face a street unless a second street-facing entrance existed before the ADU was created.

Ordinance read August 2026

Bethlehem's Zoning Ordinance contains no accessory dwelling unit use at all. The only second unit the code allows beside a house is a 'Unit for Care of Relative', which Section 1304.01(b)(5) marks 'P' (permitted by right, decided by the Zoning Officer) in every residential district: RR Rural Residential, RS Single Family, RG Medium Density, RT High Density and R-RC Residential Retirement Complex. It may be detached: Section 1322.03(bbb)(3) expressly contemplates 'a modular cottage that will be completely removed from the lot after the relative no longer resides within the unit' and allows a lawful detached garage to be converted into one. The conditions bite hard, though: occupancy is capped at two people who must be relatives of the permanent residents of the principal dwelling, at least one of whom needs the accommodation because of illness, old age or disability, and the unit must be reconvertible or removable once they leave. Outside residential zones the same accessory use is permitted on the lot of an existing dwelling in the CL, CG, CB and IR districts.

Ordinance read August 2026

The same Unit for Care of Relative may be attached or internal, but Section 1322.03(bbb)(8) requires 'an internal doorway that connects the main dwelling unit to the unit for the relative' and (9) allows only one entry door facing a public street, so it cannot read as an independent apartment. A genuinely separate second dwelling unit is possible only through 'Conversion of an Existing One Family Dwelling into Two or More Dwelling Units', and that is a special exception before the Zoning Hearing Board available only in the RG and RT districts (not permitted in RR, RS or R-RC). Section 1322.03(o)(6) limits it further: 'If the building is currently a one family dwelling, it shall not be converted to two or more dwelling units unless the building included more than 3,000 square feet of habitable floor area prior to the enactment of this Ordinance.' Section 1302.41 also bars a second kitchen in a dwelling unit 'unless it is for the purpose of accommodating a relative who needs special care and supervision because of age or disability', which closes the informal internal-ADU route.

Ordinance read August 2026

Lancaster has no accessory dwelling unit category, so a backyard unit is treated as a second principal dwelling. Section 300-83 provides that in any residential district any structure containing a dwelling unit is a principal building, and Section 300-28 then allows more than one principal building on a single lot where a land development plan complies and where the yard and other requirements are met for the entire lot regardless of the number of buildings. A new single-family detached dwelling is a permitted-by-right use in the R1, R2, R3, R4, RO and MU Districts, and Section 300-44E expressly anticipates a lot with an existing single-family dwelling where a second residential unit is proposed in a separate building. The catch is process and dimensions: two residential buildings on one lot is land development, so a plan is required, and once a garage holds a dwelling it is a principal building subject to the 25-foot rear yard (30 feet in R1) rather than the three-foot accessory-structure setback.

Ordinance read August 2026

An internal or attached second unit means converting the house into a two-family dwelling, and the Table of Permitted Uses gates that hard. Conversion of an existing building to a two-family dwelling is a Zoning Hearing Board special exception in the R3, R4, RO, MU, C1 and C2 Districts and only where the building is at least 2,000 gross square feet; it is by right only in CB1 (never at street level) and CB. It is not listed at all in R1 or R2, and § 300-15 provides that uses not specifically permitted in a district are prohibited, so a duplex conversion is simply unavailable in those two districts. A brand-new two-family dwelling is a special exception in MU and by right only in CB1 and CB. Table note (3) permits a below-threshold conversion only where the structure contains a nonresidential use and is not a single-family dwelling, so a small house cannot be split.

Ordinance read August 2026

The route depends on the form of the unit and the district. A second detached dwelling is a by-right use in R1 through R4, RO and MU, so the zoning step is a certificate of zoning compliance signed by the Zoning Officer under § 300-60, with no hearing. The land development step is where it splits: § 265-21B(7) makes conversion of an accessory structure to a residential unit a minor plan, processed by City staff rather than the Planning Commission and decided within 45 days, whereas a newly built backyard dwelling is not on the minor list and goes through the full preliminary and final plan process before the Planning Commission. An internal conversion to a two-family dwelling runs the other way: it needs a Zoning Hearing Board special exception hearing in R3, R4, RO and MU, but Chapter 265 excludes conversion of an existing building into not more than three residential units from land development, so no plan is needed unless the units will be condominiums.

Ordinance read August 2026

Lower Merion has no general accessory dwelling unit use: Table 5.1, Uses, has no ADU line for the LDR or MDR residential districts, so a market-rate backyard cottage for an unrelated tenant is not available on an ordinary Main Line lot. Two narrow paths exist. Under § 155-10.2C, Restricted accessory dwelling units, a single-family dwelling in the LDR, MDR, IC and IH Districts may be converted into two units, and Subsection C(6) expressly contemplates the unit sitting in an accessory structure, which must then meet the principal building setbacks of the underlying district; the price is that every occupant of both units must be related by blood, marriage or legal adoption or be domestic partners, and the accessory unit is limited to two people, one of whom is 62 or older. The second path is preservation-based: for a property carried on the township's Historic Resource Inventory as a Class 1 or Class 2 Historic Resource, Table 7.1.1 lists 'Accessory dwelling unit' as a regulated (R) use, and § 155-2.1 defines an ADU as a dwelling unit sharing a lot with a principal building 'that may or may not be in a separate structure.' A detached unit is therefore reachable only through the elder-family special exception or through historic designation.

Ordinance read August 2026

The attached or internal case is what § 155-10.2C is written around: in the LDR, MDR, IC and IH Districts 'a single-family dwelling or an existing institutional building may be converted into two dwelling units, each with its own cooking facilities,' subject to ten conditions including the family-relationship rule, the age-62 occupancy limit, a recorded agreement to remove the second kitchen when the qualifying use ends, and an annual township permit. Table 5.1 makes the parent use, Alternative housing for the elderly, a special exception in LDR and MDR (Table 5.2 makes it permitted by right only in the IC and IH institutional districts), so a basement or addition unit rented to an unrelated tenant has no approval path. For a Class 1 or Class 2 Historic Resource, Table 7.1.2 allows an accessory dwelling unit as a regulated use with just two conditions: it must be the only dwelling unit besides the principal dwelling, and it must satisfy Table 8.1 parking. § 155-7.1B(4)(a) also requires an added historic-resource use to be 'contained within the historic buildings or structures unless otherwise specifically permitted,' which favors conversions inside the historic house or an existing carriage house over new construction.

Ordinance read August 2026

There is no flat owner-occupancy mandate, but the elder-conversion path effectively requires the owner or a sponsoring nonprofit on site. § 155-10.2C(1) requires that all individuals living in the two dwelling units be related by blood, marriage or legal adoption or be domestic partners, and C(10) adds that if the facility is not owner-occupied its use must be sponsored by a nonprofit organization whose purpose includes housing the elderly and overseeing residents' care, with a designated agent or offices in Pennsylvania. The historic-resource accessory dwelling unit in Table 7.1.2 carries no owner-occupancy condition at all. Pennsylvania preempts nothing here: the Municipalities Planning Code leaves owner-occupancy conditions entirely to the municipality, and no statewide ADU act has been enacted.

Ordinance read August 2026

Approval depends entirely on which path the unit uses. In LDR and MDR, Alternative housing for the elderly, the use that carries the § 155-10.2C restricted accessory dwelling unit, is an 'S' use: a special exception decided by the Zoning Hearing Board after a public hearing (Table 5.1; § 155-5.1E(4)), and Table 5.3 adds that in a Class 1 Historic Resource the same use requires conditional-use approval from the Board of Commissioners instead. Approved units then need an annual township permit under § 155-10.2C(8), and the zoning permit expires six months after the building stops being occupied by the qualifying elderly resident. By contrast, on a Class 1 or Class 2 Historic Resource an accessory dwelling unit is a regulated 'R' use, which § 155-7.1D(2) makes 'subject to administrative approval by the issuance of a zoning permit by the Zoning Officer.' In the IC and IH institutional districts the elderly-housing use is permitted by right (Table 5.2). Budget for a hearing unless the property is a designated historic resource.

Ordinance read August 2026

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.

Ordinance read August 2026

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).

Ordinance read August 2026

There is no administrative route to an ADU in Pittsburgh today. Inside an ADU Overlay District the unit itself would be an accessory use subject only to the § 912.08.E standards plus a Certificate of Occupancy and a recorded deed restriction, with no Zoning Board hearing. Creating the district, however, is legislative: § 912.08.C requires that adoption of both a preliminary and permanent ADU Overlay District proceed 'in accordance with the Zoning Map and Text Amendment Procedures of Section 922.05', which means a Planning Commission public hearing and recommendation followed by a City Council ordinance. Because an individual homeowner realistically cannot obtain that, the review path is recorded here as discretionary rather than permitted.

Ordinance read August 2026

Not reached: because Reading authorizes no accessory dwelling unit, no owner occupancy condition attaches to one, and Chapter 600 imposes no owner occupancy requirement on any residential use. Section 600-902F instead limits each dwelling unit to occupancy by one household meeting the chapter's definition of family, which caps unrelated occupants at three. Two adjacent rules exist and are easy to mistake for an ADU owner occupancy test: section 308-102 requires owners of residential and mixed-use parcels to obtain and renew a city housing registration, excusing owner-occupied single-family properties that confirm owner occupancy, and section 600-1108B(1) requires a short-term rental's record owner or designated manager to reside or keep an office within 30 miles of the unit.

Ordinance read August 2026

There is no ADU permit path to classify. A zoning permit is required before creating a new use or increasing the number of dwelling units on a property (section 600-301A(2)(a)[3] and [7]), but the Zoning Administrator may issue a by-right permit only for a use shown as permitted in the applicable district (section 600-301B(1) and section 600-602), and no district schedule lists an accessory apartment. Special exception and conditional use permits are likewise unavailable because neither list includes an accessory dwelling. The only theoretical route is a use variance from the Zoning Hearing Board under section 600-406D, which requires proof of unnecessary hardship, a discretionary and rarely granted remedy rather than a permit type.

Ordinance read August 2026

A new backyard cottage cannot be built in Upper Darby. Section 550-17B(1) allows an accessory dwelling only where it is 'physically connected to the principal dwelling unit' or is 'a converted existing detached building which maintains the same footprint,' so the detached pathway is a conversion of a garage or other existing outbuilding with no enlargement of its footprint. Even that requires a special exception: Table 3-1 of the Table of Permitted Uses marks 'Accessory dwelling' as S in all six residential districts (R-C, R-C-1, R-1, R-2, R-3, R-4) and leaves the cell blank in C-1 through C-4 and REC, where the use is therefore prohibited. Section 550-17B(3) limits the host property to a single-family detached or single-family semidetached dwelling, which excludes the row homes, twins-over-twins and apartment buildings that make up much of the Township, and B(7) requires a detached unit to use the principal dwelling's existing driveway with no new driveway created.

Ordinance read August 2026

An attached or internal accessory dwelling (an addition or an in-law suite carved out of the house) is the primary pathway, but it is never by right. It is a special exception in every residential district under Table 3-1, so it takes a noticed Zoning Hearing Board hearing. Section 550-17B(3) allows the unit only in a single-family detached or single-family semidetached dwelling, B(4) requires it to share the principal dwelling's sewage disposal and water supply systems (no separate service laterals), B(5) caps occupancy at two people, and B(2) limits those occupants to people related by blood, adoption or marriage to the occupants of the principal dwelling. B(6) requires compliance with the minimum space and habitable living area rules of the applicable housing and building codes. The practical result is a family suite, not an independent rentable second unit.

Ordinance read August 2026

Every accessory dwelling in Upper Darby needs a discretionary Zoning Hearing Board approval. Table 3-1 marks the use S, defined in § 550-8A as 'a use that is permitted only by approval by the Zoning Hearing Board,' and § 550-53A confirms that permits for special exception uses 'shall be issued only upon order of the Zoning Hearing Board.' The Board holds a public hearing noticed by publication once a week for two successive weeks plus mailed notice to the applicant, the Mayor, Council, the Zoning Officer and the Delaware County Planning Department (§ 550-54G), and it weighs the open-ended criteria in § 550-54J, including neighborhood character and the effect on adjacent property, with power to attach conditions. The Township's current application form (Zoning Hearing Board Petition for Variance or Special Exception, version 5.28.26) lists a nonrefundable residential fee of $750 for up to two reliefs. An approval expires after one year if no building permit is obtained (§ 550-54H); after approval the applicant still needs a zoning use permit and a zoning certificate of occupancy under § 550-53B, C and E.

Ordinance read August 2026