ADU rules in Lancaster

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.

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.

Because there is no accessory dwelling unit category there is no percent-of-primary-dwelling or square-foot ceiling to hit. What binds instead is § 300-30's minimum habitable floor area: 400 square feet for an efficiency unit, 550 for one bedroom, 700 for two, 950 for three, 1,100 for four, plus 200 per additional bedroom. The Table of Height, Area and Bulk Regulations then caps the whole lot: 2 1/2 stories and 35 feet with 35% maximum building coverage in R1 and R2, and 3 stories and 38 feet with 45% building coverage for single-family detached dwellings in R3, R4, RO, MU, C1 and C2. Minimum lot area for a single-family detached dwelling is 10,000 square feet in R1, 4,000 in R2 and 3,500 in R3, R4, RO, MU, C1 and C2. Attachment 3 note (d) waives lot area, lot width, lot depth, front yard, side yard, height and building coverage for conversions that do not expand an existing building, provided nonconforming lot coverage is not increased and required parking is provided; the rear yard is not on that waiver list.

Chapter 300 imposes no owner-occupancy condition on dwelling units, and Pennsylvania has no statewide ADU statute either requiring or forbidding one. The owner-occupancy rules that do exist in the ordinance attach to other things: in the R1 and R2 Districts a nonfamily unit (a dwelling unit occupied by up to three unrelated people) must be occupied by at least one owner of record, a homestay requires the owner to be residing in the dwelling unit for the duration of the rental, and a bed-and-breakfast must be owner-occupied or manager-occupied. A conventional long-term second unit carries none of these. Chapter 238's rental licensing likewise does not require owner occupancy; it only exempts certain owner-occupied arrangements from needing a license at all.

Section 300-41A requires one off-street space per dwelling and/or efficiency unit in all districts except CB and CB1, so a second unit normally adds one space. Section 300-44C then dictates where it goes: in residential districts other than R1 parking must be in the rear yard or to the rear or side of the building, accessed from the rear lot line or from a secondary front or side yard on a corner lot, on a surface that is not stone or gravel, and at least three feet from any side lot line. Where that is impossible, § 300-44E lets the owner seek a special exception to reduce or waive the requirement, and it names this situation explicitly: lots with an existing single-family dwelling where a second residential unit is proposed in a separate building under § 300-28A. The applicant must supply a parking study of everything within 300 feet, counted at three different times of day and week, and the study's author must appear to testify. Nonfamily units need two spaces, not one.

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.

A second unit can be rented long term, but every residential rental unit needs a City rental property license under Chapter 238, Article I, which City Council repealed and replaced in its entirety by Ordinance No. 03-2026 (adopted 3-10-2026, effective 20 days later). The license runs two years and issuance requires demonstrating compliance with Zoning Ordinance 300, an inspection, and no outstanding City fees or taxes. Section 238-3B exempts only three cases: renting to a spouse, parent, child, grandchild or grandparent when the owner does not live at the property; an owner living there full time as a primary residence who rents rooms to no more than two additional non-family renters; and an owner living there full time and operating a homestay. Short-term rental is a distinct commercial-service use permitted by right only in RO, MU, CB1, CB, C1 and C2, never in R1 through R4, and carries mandatory conditions including registration as a transient dwelling rental unit with a Housing Inspector's inspection, a named property manager, a 30-consecutive-day cap, whole-dwelling rental in one person's name and no more than two adults per bedroom. Homestays (owner present, at most two bedrooms) are by right in R3, R4, RO, MU, CB1, CB, C1 and C2.