Combined sanitary and storm sewers are not permitted in new installations. All sanitary and storm systems shall be separate up to a point within 5 feet (1524 mm) inside or outside of the foundation wall, unless rules of the Department of Environmental Protection require that the point of combination be located otherwise. With respect to repair of combined systems installed prior to the effective date of this section, the size of a combination sanitary and storm drain or sewer shall be computed in accordance with the method in Section 1106.3. The fixture units shall be converted into an equivalent projected roof or paved area. Where the total fixture load on the combined drain is less than or equal to 256 fixture units, the equivalent drainage area in horizontal projection shall be taken as 1,333 square feet (124 m2). Where the total fixture load exceeds 256 fixture units, each additional fixture unit shall be considered the equivalent of 5.2 square feet (0.48 m2) of drainage area. These values are based on a rainfall rate of 3 inch (75 mm) per hour.