Framing (construction)


Framing, in construction, is the fitting together of pieces to give a structure, particularly a building, support and shape. Framing materials are usually wood, engineered wood, or structural steel. The alternative to framed construction is generally called mass wall construction, where horizontal layers of stacked materials such as log building, masonry, rammed earth, adobe, etc. are used without framing.
Building framing is divided into two broad categories, heavy-frame construction if the vertical supports are few and heavy such as in timber framing, pole building framing, or steel framing; or light-frame construction if the supports are more numerous and smaller, such as balloon, platform, light-steel framing and pre-built framing. Light-frame construction using standardized dimensional lumber has become the dominant construction method in North America and Australia due to the economy of the method; use of minimal structural material allows builders to enclose a large area at minimal cost while achieving a wide variety of architectural styles.
Modern light-frame structures usually gain strength from rigid panels, but until recently carpenters employed various forms of diagonal bracing to stabilize walls. Diagonal bracing remains a vital interior part of many roof systems, and in-wall wind braces are required by building codes in many municipalities or by individual state laws in the United States. Special framed shear walls are becoming more common to help buildings meet the requirements of earthquake engineering and wind engineering.

History

Historically, people fitted naturally shaped wooden poles together as framework and then began using joints to connect the timbers, a method today called traditional timber framing or log framing. In the United States, timber framing was superseded by balloon framing beginning in the 1830s. Balloon framing makes use of many lightweight wall members called studs rather than fewer, heavier supports called posts; balloon framing components are nailed together rather than fitted using joinery. The studs in a balloon frame extend two stories from sill to plate. Platform framing superseded balloon framing and is the standard wooden framing method today. The name comes from each floor level being framed as a separate unit or platform. The use of factory-made walls and floors has shown an increase in popularity due to the time-saving and cost-efficiency. Walls are made usually in facilities and then shipped to the different job sites. This process of framing has improved the speed of framing on site.
Framed construction was rarely used in Scandinavia before the 20th century because of the abundant availability of wood, an abundance of cheap labour, and the superiority of the thermal insulation of logs. Hence timber framing was used first for unheated buildings such as farm buildings, outbuildings and summer villas, but for houses only with the development of wall insulation.

Walls

Wall framing in house construction includes the vertical and horizontal members of exterior walls and interior partitions, both of bearing walls and non-bearing walls. These stick members, referred to as studs, wall plates and lintels, serve as a nailing base for all covering material and support the upper floor platforms, which provide the lateral strength along a wall. The platforms may be the boxed structure of a ceiling and roof, or the ceiling and floor joists of the story above. In the building trades, the technique is variously referred to as stick framing, stick and platform, or stick and box, as the sticks give the structure its vertical support, and the box-shaped floor sections with joists contained within length-long post and lintels, support the weight of whatever is above, including the next wall up and the roof above the top story. The platform also provides lateral support against wind and holds the stick walls true and square. Any lower platform supports the weight of the platforms and walls above the level of its component headers and joists.
In some countries, framing lumber is subject to regulated standards that require a grade-stamp, and a moisture content not exceeding 19%.
There are four historically common methods of framing a house.
  • Post and beam, which is now used predominantly in barn construction.
  • Braced frame construction, also known as full frame, half frame, New England braced frame, combination frame an early form of light framing which survived into the 1940s in the northeastern United States, defined by the continued use of girts, corner posts, and braces, most often mortised, tenoned, and pegged with nailed studs.
  • Balloon framing using a technique suspending floors from the walls was common until the late 1940s, but since that time, platform framing has become the predominant form of house construction.
  • Platform framing often forms wall sections horizontally on the sub-floor prior to erection, easing positioning of studs and increasing accuracy while cutting the necessary manpower. The top and bottom plates are end-nailed to each stud with two nails at least in length. Studs are at least doubled at openings, the jack stud being cut to receive the lintels that are placed and end-nailed through the outer studs.
Wall sheathing, usually a plywood or other laminate, is usually applied to the framing prior to erection, thus eliminating the need to scaffold, and again increasing speed and cutting manpower needs and expenses. Some types of exterior sheathing, such as asphalt-impregnated fiberboard, plywood, oriented strand board and waferboard, will provide adequate bracing to resist lateral loads and keep the wall square. Others, such as rigid glass-fiber, asphalt-coated fiberboard, polystyrene or polyurethane board, will not. In this latter case, the wall should be reinforced with a diagonal wood or metal bracing inset into the studs. In jurisdictions subject to strong wind storms local codes or state law will generally require both the diagonal wind braces and the stiff exterior sheathing regardless of the type and kind of outer weather resistant coverings.
Finally, the outside of the wall sheathing will usually be covered with siding, to protect it from the elements and for decorative reasons.

Corners

A multiple-stud post of at least 3 three studs, is generally used at exterior corners and intersections to secure a good tie between adjoining walls. It provides nailing support for interior finishes and exterior sheathing. Corners and intersections, however, must be framed with at least two studs.
Nailing support for the edges of the ceiling is required at the junction of the wall and ceiling where partitions run parallel to the ceiling joists. This material is commonly referred to as dead wood or backing.

Exterior wall studs

Wall framing in house construction includes the vertical and horizontal members of exterior walls and interior partitions. These members, referred to as studs, wall plates and lintels, serve as a nailing base for all covering material and support the upper floors, ceiling and roof.
Exterior wall studs are the vertical members to which the wall sheathing and cladding are attached. They are supported on a bottom plate or foundation sill and in turn support the top plate. Studs usually consist of or lumber and are commonly spaced at on center. This spacing may be changed to on center depending on the load and the limitations imposed by the type and thickness of the wall covering used. Wider -by--inch studs may be used to provide space for more insulation. Insulation beyond that which can be accommodated within a -inch stud space can also be provided by other means, such as rigid or semi-rigid insulation or batts between -by--inch horizontal furring strips, or rigid or semi-rigid insulation sheathing to the outside of the studs. The studs are attached to horizontal top and bottom wall plates of -inch lumber that are the same width as the studs.

Interior partitions

Interior partitions supporting floor, ceiling or roof loads are called loadbearing walls; others are called non-loadbearing or simply partitions. Interior loadbearing walls are framed in the same way as exterior walls. Studs are usually lumber spaced at on center. This spacing may be changed to depending on the loads supported and the type and thickness of the wall finish used.
Partitions can be built with or studs spaced at on center depending on the type and thickness of the wall finish used. Where a partition does not contain a swinging door, studs at on center are sometimes used with the wide face of the stud parallel to the wall. This is usually done only for partitions enclosing clothes closets or cupboards to save space. Since there is no vertical load to be supported by partitions, single studs may be used at door openings. The top of the opening may be bridged with a single piece of lumber the same width as the studs. These members provide a nailing support for wall finish, door frames and trim.

Lintels (headers)

Lintels are the horizontal members placed over window, door and other openings to carry loads to the adjoining studs. Lintels are usually constructed of two pieces of 2 in lumber separated with spacers to the width of the studs and nailed together to form a single unit. Lintels are predominately nailed together without spacers to form a solid beam and allow the remaining cavity to be filled with insulation from the inside. The preferable spacer material is rigid insulation. The depth of a lintel is determined by the width of the opening and vertical loads supported.

Wall sections

The complete wall sections are then raised and put in place, temporary braces added and the bottom plates nailed through the subfloor to the floor framing members. The braces should have their larger dimension on the vertical and should permit adjustment of the vertical position of the wall.
Once the assembled sections are plumbed, they are nailed together at the corners and intersections. A strip of polyethylene is often placed between the interior walls and the exterior wall, and above the first top plate of interior walls before the second top plate is applied to attain continuity of the air barrier when polyethylene is serving this function.
A second top plate, with joints offset at least one stud space away from the joints in the plate beneath, is then added. This second top plate usually laps the first plate at the corners and partition intersections and, when nailed in place, provides an additional tie to the framed walls. Where the second top plate does not lap the plate immediately underneath at corner and partition intersections, these may be tied with galvanized steel plates at least wide and long, nailed with at least three nails to each wall.