Upper Darby, PA Accessory Structures: ADU Rules (2026)

Section 550-17B treats accessory dwellings as a special exception use in residential districts, meaning approval requires a hearing before the Upper Darby Zoning Hearing Board rather than a routine permit. Seven conditions apply: the ADU must be physically connected to the principal dwelling or be a converted existing detached building that keeps its existing footprint; it is permitted only in a single-family detached or single-family semidetached dwelling, not in twins converted from other configurations or in multifamily buildings; it must share the same sewage disposal and water supply systems as the principal dwelling, so a separate well or septic system is not allowed; occupancy is capped at two people; the unit must meet the minimum space and habitable living area requirements of the applicable housing or building codes; and, if the ADU sits in a detached accessory building, it must use the principal dwelling's existing driveway, with no new driveway permitted.

Because this is a special exception, the applicant must also satisfy the general special exception review criteria in § 550-54J and the underlying zoning district's dimensional standards under § 550-17A, on top of the seven ADU-specific conditions. The Zoning Officer cannot issue a permit for an accessory dwelling on their own authority under § 550-53A; only the Zoning Hearing Board can grant it after a public hearing.