ADU rules in Lehigh County, PA — also called accessory dwelling unit regulations or granny flat ordinances — cover setbacks, owner-occupancy, parking, and permit requirements.
Pennsylvania has no statewide ADU mandate. Under the Pennsylvania Municipalities Planning Code (MPC, Act 247 of 1968, 53 P.S. §10101 et seq.), zoning authority rests with municipalities (boroughs, townships, cities) - not Lehigh County itself. Each of Lehigh County's 24 municipalities (1 city, 23 boroughs/townships) decides whether ADUs are permitted, what size limits apply, and whether a special exception or variance is required. The City of Allentown's Zoning Ordinance (Ordinance No. 16166, adopted October 15, 2025) is the controlling document for the county seat.
Pennsylvania is a strong-municipal-zoning state. The Municipalities Planning Code (Act 247 of 1968), codified at 53 P.S. §10101 et seq., grants comprehensive zoning authority to municipalities. Section 603 of the MPC (53 P.S. §10603) sets out the permitted contents of municipal zoning ordinances - including provisions for accessory uses, density bonuses (Section 603(c)(6) for affordable housing), and dimensional standards. Pennsylvania counties have very limited zoning power; under MPC Section 301 et seq., a county zoning ordinance applies only in municipalities that have not adopted their own. Lehigh County does not administer a countywide zoning ordinance for parcels inside municipalities that have adopted their own zoning - which is the case for all 24 municipalities. As a result, ADU rules are entirely municipal. The City of Allentown adopted a comprehensive new Zoning Ordinance (No. 16166) on October 15, 2025; Article 6 governs accessory structures and uses. Other Lehigh County jurisdictions (Bethlehem, Emmaus, Macungie, Catasauqua, Coopersburg, Fountain Hill, Slatington, Alburtis, Coplay, and the surrounding townships) each maintain separate zoning ordinances. Property owners must check with their specific municipal zoning officer - not the county - to determine whether an ADU (also called a 'granny flat,' 'in-law suite,' or 'accessory apartment') is permitted by right, as a special exception, or prohibited in their zoning district.
Constructing an ADU without the required municipal zoning approval and building permit violates the local zoning ordinance and the Pennsylvania Uniform Construction Code (35 P.S. §7210.101 et seq.). Enforcement is by the municipal zoning officer under MPC §616.1 (53 P.S. §10616.1), with notices of violation, civil enforcement actions in the magisterial district court, and fines of up to $500 per day per MPC §617.2.
Lehigh County, PA
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