Bethlehem, PA Accessory Structures: ADU Rules (2026)

Pennsylvania, unlike a growing number of "ADU preemption" states, regulates accessory dwelling units exclusively at the municipal level. The legal foundation for housing regulation in Pennsylvania is the Municipalities Planning Code (Act 247 of 1968, as amended; 53 P.S. §10101 et seq.), which authorizes cities, boroughs, and townships to adopt zoning ordinances, defines the role of zoning hearing boards, and sets the legal framework for variances, special exceptions, and conditional uses. The Bethlehem Zoning Ordinance, last comprehensively rewritten around 2023, divides the city into residential, commercial, industrial, and mixed-use districts. Whether an ADU is allowed by right, by special exception, or by conditional use depends on the underlying district, lot size, and lot configuration. Owner-occupancy requirements, off-street parking minimums, minimum and maximum unit sizes, separate-entrance rules, short-term-rental limitations, and design standards are set by the Bethlehem Zoning Ordinance rather than state law. Variances and special exceptions are heard by the Bethlehem Zoning Hearing Board, which operates under 53 P.S. §§10901-10916. Building construction must additionally comply with the Pennsylvania Uniform Construction Code at 34 Pa Code §§401.1-405.42, which adopts the 2018 IRC and IBC with state amendments. Because Bethlehem includes historic Moravian-era housing stock in the Historic Bethlehem district and post-industrial South Bethlehem (the former Bethlehem Steel area), ADU additions frequently raise lot-coverage and setback issues that may require Zoning Hearing Board relief.