Low Density
Side-by-Side
Twin
Form: Two units with one shared vertical wall, three open sides, and external entrances. Twins are also known as duplex (side-by-side) outside of the region. Units may be located on one or separate parcels. Missing middle twins generally lack frontal garages. From the outside twins will appear as small to medium single-unit houses.
Local presence: Twins are found throughout the county. Traditionally twins were built meeting missing middle forms, while many twins continue to be built, many are too large to be considered missing middle housing.
Zoning considerations: Municipalities should consider encouraging the development of twin units by allowing twins by-right. This may require amending districts currently allowing twins by special exception or conditional use or expanding the districts where twins are permitted. Additional municipal considerations as they relate to twins include: permitting smaller minimum lot sizes, requiring sidewalk construction and utility connections for new units, and ensuring setbacks are at an appropriate size to maintain neighborhood integrity.
Zoning ordinance examples
- Phoenixville Borough: Permits twin development, as defined in section 27-202, throughout the borough. Units must be on individual parcels, each with a minimum lot area of 3,000 square feet. Specific provisions related to twins are contained in Zoning District Specifications (Section 27-302).
- West Goshen Township: Permits as a special exception twins (units separated by a party wall with independent outside access and open space on three sides) and duplexes (single buildings containing two dwelling units with independent outside access, and open on all sides) under semidetached buildings in R-4 Residential District zoning. The township requires sewer connections for each semidetached unit.
- Kennett Square Borough: Defines single-family semi-detached (twin) dwellings, as two connected one-family dwellings sharing a common vertical, each on separate lots with yard access on three sides in. Twins are allowed by-right in R-3 Residential, C-2 Secondary commercial districts, and under density bonus provisions as a cluster development option.
