Old-House Lumber & Framing Systems
Most wood-frame houses built in the latter half of the 20th century use a platform-framing system. But many earlier stick-framed houses use the "balloon" system.
The main difference between platform and balloon framing is at the floor lines. The balloon wall studs extend from the sill of the first floor all the way to the top plate or end rafter of the second floor. The platform-framed wall, on the other hand, is complete for each floor.
In balloon framing, both the wall studs and the floor joists rest on a sill anchored to the foundation. The studs and joists typically are toe-nailed to the still with eight-penny nails and nailed to each other with at least three ten-penny nails.
The ends of the second-floor joists rest on a 1- by 4-inch ribbon that has been let into the studs. In addition, the joists are nailed with four ten penny nails to the studs at these connections.The end joists parallel to the outside walls on the first and second floors are also nailed to each stud.
In most areas, current building codes require that firestops be used in balloon framing to prevent the spread of fire through open wall passages -- although these firestops may or may not be present in older houses.
The firestops are typically 2 by 4 inch blocking placed between the studs.
Major Source: Wood-Frame House Construction by L.O. Anderson, originally published as Agriculture Handbook No. 73 in 1970 by the U.S. Government Printing Office and prepared by the Department of Agriculture.