Balloon framing is a method of wood construction used primarily in Scandinavia, Canada and the United States. In the U.S., this method was introduced by Augustine Taylor (1796-1891) in Chicago. It utilizes long continuous framing members (studs) that run from sill to eave line with intermediate floor structures nailed to them. Once popular when long lumber was plentiful, balloon framing has been largely replaced by platform framing.
The curious name of this framing technique was originally a derisive one. As Taylor was constructing his first such building, St. Mary's Church, in 1833, skilled carpenters looked on at the comparatively thin framing members, all held together with nails, and declared this method of construction to be no more substantial than a balloon. It would surely blow over in the next wind! Though the criticism proved baseless, the name stuck.
Although lumber was plentiful in 19th century America, skilled labor was not. The advent of cheap machine-made nails, along with water-powered sawmills, in the early 19th century made balloon framing highly attractive, because it did not require highly-skilled carpenters, as did the dovetail joints, mortises and tenons required by post-and-beam construction. For the first time, any farmer could build his own buildings without a time-consuming learning curve.
It has been said that balloon framing populated the western United States and the western provinces of Canada. Without it, western boomtowns certainly could not have blossomed overnight. It is also a fair certainty that, by radically reducing construction costs, balloon framing improved the shelter options of poorer North Americans.
The main difference between platform and balloon framing is at the floor lines. The balloon wall studs extend from the sill of the first story all the way to the top plate or end rafter of the second story. The platform-framed wall, on the other hand, is independent for each floor.
Balloon framing has several disadvantages as a construction method:
- The first is the creation of a path for fire to readily travel from floor to floor. This is mitigated with the use of firestops at each floor level.
- Second is the lack of a working platform for work on upper floors. Whereas workers can readily reach the top of the walls being erected with platform framing, balloon construction requires scaffolding to reach the tops of the walls (which are often two or three stories above the working platform).
- The requirement for long framing members is a third disadvantage.
- A fourth disadvantage, in certain larger buildings, is a noticeable down-slope of floors towards central walls, caused by the differential shrinkage of the wood framing members at the perimeter versus central walls. Larger balloon-framed buildings will have central bearing walls which are actually platform framed and thus will have horizontal sill and top plates at each floor level, plus the intervening floor joists, at these central walls. Wood will shrink much more across its grain than along the grain. Therefore, the cumulative shrinkage in the center of such a building is considerably more than the shrinkage at the perimeter where there are much fewer horizontal members. Of course, this problem, unlike the first three, takes time to develop and become noticeable.
Balloon framing has been outlawed by building codes in many areas because of the fire danger that it poses.
Balloon framing is growing in popularity again in light gauge steel stud construction. For light gauge steel, long framing members are not as much of an issue. Balloon framing provides a more direct load path down to the foundation. Some electricians like working in balloon frame buildings, because the lack of fire blocking makes it much easier to add circuits.
Platform framing is a light-frame construction system and the most common method of constructing the frame for houses and small apartment buildings as well as some small commercial buildings in Canada and the United States.
The framed structure sits atop a concrete (most common) or treated wood foundation. A Sill-Plate is anchored, usually with 'J' bolts to the foundation wall. Generally these plates must be pressure treated to keep from rotting. The bottom of the sill-plate is raised a minimum 6 inches above the finished grade by the foundation. This again is to prevent the sill-plate from rotting as well as providing a termite barrier.
The floors, walls and roof of a framed structure are created by assembling (using nails) consistently sized framing elements of dimensional lumber (2×4, 2×6, etc.) at regular spacings (12″, 16″, and 24″ on center), forming stud-bays (wall) or joist-bays (floor). The floors, walls and roof are typically made torsionally stable with the installation of a plywood or composite wood “skin” referred to as sheathing. Sheathing has very specific nailing requirements (such as size and spacing); these measures allow a known amount of shear force to be resisted by the element. Spacing the framing members properly allows them to align with the edges of standard sheathing. In the past, tongue and groove planks installed diagonally were used as sheathing. Occasionally, wooden or galvanized steel braces are used instead of sheathing. Two examples of such steel frames are Simpson Steel Strong-Walls, and Hardy Frames.
The floor, or the platform of the name, is made up of joists (usually 2x6, 2×8, 2×10 or 2×12, depending on the span) that sit on supporting walls, beams or girders. The floor joists are spaced at (12″, 16″, and 24″ on center) and covered with a plywood subfloor. In the past, 1x planks set at 45-degrees to the joists were used for the subfloor.
Where the design calls for a framed floor, the resulting platform is where the framer will construct and stand that floor’s walls (interior and exterior load bearing walls and space-dividing, non-load bearing “partitions&rdquo. Additional framed floors and their walls may then be erected to a general maximum of four in wood framed construction. There will be no framed floor in the case of a single-level structure with a concrete floor known as a “slab on grade”.
Stairs between floors are framed by installing stepped “stringers” and then placing the horizontal “treads” and vertical “risers”.
A framed roof is an assembly of rafters and wall-ties supported by the top story’s walls. Prefabricated and site-built trussed rafters are also used along with the more common stick framing method. “Trusses” are engineered to redistribute tension away from wall-tie members and the ceiling members. The roof members are covered with sheathing or strapping to form the roof deck for the finish roofing material.
Floor joists can be engineered lumber(trussed, i-beam, etc.), conserving resources with increased rigidity and value. They allow access for runs of plumbing, HVAC, etc. and some forms are pre-manufactured.
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