Franklin Township, PA Accessory Structures: ADU Rules (2026)

Zoning Code § 27-1712 lets a Franklin Township property owner add an additional dwelling unit, defined as a second unit within a single-family dwelling or in a detached accessory structure on the same lot. How many units, and where, depends on acreage. 5 acres or less, one ADU is allowed, and it must be inside the principal structure. 5 acres but under 10 acres, one ADU is allowed either inside the principal structure or inside a detached accessory structure. On properties of 10 acres or more, up to two ADUs are allowed, one inside the principal structure and a second inside a detached accessory structure.

Placing an ADU in a detached accessory structure requires land development approval under § 22-202, and that detached structure must meet the setback requirements for a principal dwelling in its zoning district. Every ADU needs a separate street address if it's detached, must use the existing driveway where possible (or obtain a driveway permit under § 21-125), needs one additional off-street parking space, and triggers Chapter 19 stormwater management review for any new impervious cover. Chester County Health Department sewage approval is required for every ADU, plus a Health Department well permit if a new well is needed, and both a zoning permit and a Uniform Construction Code building permit are required before construction.