ADU rules in Allegheny County, PA — also called accessory dwelling unit regulations or granny flat ordinances — cover setbacks, owner-occupancy, parking, and permit requirements.
Allegheny County has no countywide ADU mandate. Pennsylvania does not require municipalities to permit accessory dwelling units. Most Allegheny County municipalities limit ADUs to specific zoning districts or prohibit them outright. Pittsburgh allows ADUs citywide as of 2023 zoning amendments.
Under the PA Municipalities Planning Code (Act 247), ADU authority rests entirely with local zoning ordinances. Pittsburgh amended its zoning code in 2023 to allow ADUs (interior, attached, or detached) in all residential districts with parcel-size and height limits. Many suburban Allegheny County municipalities either prohibit ADUs or permit them only as in-law suites within the primary dwelling. Permits require PA UCC compliance (building, plumbing, electrical, mechanical) and separate utility metering is generally not required but allowed. Short-term rental of ADUs is governed by separate STR rules.
Zoning violations: $500 per day per PA MPC. Building without UCC permit: stop-work orders, doubled permit fees, and potential misdemeanor charges.
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See how Allegheny County's adu rules rules stack up against other locations.
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