Dwelling units in two-family dwellings are required to be separated from each other by wall and/or floor assemblies, of not less than two-hour masonry fire-resistant construction, from the crawl space or basement up through the attic to the roof. Fire-resistive floor, ceiling and wall assemblies shall extend to and be tight against the exterior wall, and wall assemblies shall extend to the underside of the roof sheathing. The roof sheathing within 4 feet of the fire wall is required to be fire rated.
Wall and floor assemblies separating dwelling units shall provide airborne and impact sound insulation for floor/ceiling assemblies. These assemblies shall meet a sound transmission class of 45.