Harrisburg, PA Accessory Structures: ADU Rules (2026)

Harrisburg Codified Ordinances § 7-309.2(A) holds the whole accessory dwelling unit rule for the City of Harrisburg. It sits in Chapter 7-309, Specific Criteria, of the zoning code adopted by the Harrisburg City Council, and the subsection carries an amendment note dated 4-13-2021 (Ord. No. 6-2021).

Where the unit is allowed by right, in the RL, RM, and RF Zoning Districts, the owner skips the special exception hearing but still has to satisfy every criterion. In the CN Zoning District the same criteria apply and the unit also needs a special exception. The chapter's cross references send special exceptions and variances to Chapter 7-323, and off-street parking to Chapter 7-327. Subsection A names only RL, RM, RF, and CN; no other district is listed for this use.

Three criteria apply. First, the unit can be created within the principal residential unit or located as a detached unit on the same lot. Second, the accessory dwelling unit cannot be larger than 33% of the square footage of the principal residential unit. The code prints a percentage, not a fixed square-foot figure, so the measuring stick is the principal unit on that lot. Third, the principal residential structure must be owner-occupied.

The definitions chapter describes an accessory dwelling as a separate dwelling unit within the same principal structure or detached and situated on the same lot as the principal structure. Section 7-309.1 adds that the applicant must demonstrate compliance and furnish whatever evidence is necessary, that each use must comply with the standards of the underlying zone, and that where two or more requirements apply to the same use or structure, the requirement that is more restrictive controls. Sign, parking, and environmental performance standards still apply on top of the chapter's criteria.