Light-frame construction

Light-frame construction is a building technique based around structural members, usually called studs, which provide a stable frame to which interior and exterior wall coverings are attached, and covered by a roof comprising horizontal joists or sloping rafters covered by various sheathing materials. Modern light-frame structures usually gain strength from rigid panels used to form all or part of wall sections, but until recently carpenters employed various forms of diagonal bracing to stabilize walls. Diagonal bracing remains a vital interior part of many roof systems.

Light frame construction has become the dominant construction method throughout most of the United States and Europe because of its versatility, strength and economy. Use of minimal structural materials allows builders to enclose a large area with at a minimum cost, while achieving a wide variety of architectural styles.

Light-frame materials are most often wood or rectangular steel tubes. Preferred woods for linear structural members are usually spruce, pine or fir woods. Light frame material dimensions range from 5 cm by 10 cm (two-by-four inches) to 5 cm by 30 cm (two-by-twelve inches) at the cross-section, and lengths ranging from 2.5 m (8 feet) for walls to 7 m (20 feet) or more for joists and rafters.

Wall panels built of studs are interrupted by sections that provide rough openings for doors and windows. Openings are typically spanned by a header or lintel that bears the weight of structure above the opening. Headers are usually built to rest on trimmers, also called jacks. Areas around windows are defined by a sill, beneath the window, and cripples, which are shorter studs that span the area from the bottom plate to the sill and sometimes from the top of the window to a header, or from a header to a top plate.

Wall sections usually include a bottom plate which is secured to the structure of a floor, and one, or more often two top plates that tie walls together and provide a bearing for structures above the wall. Wood or steel floor frames usually include a rim joist around the perimeter of a system of floor joists, and often include bridging material near the center of a span to stabilize a floor against vibration and to reduce sagging along the span. In two-story construction, openings are left in the floor system for a stairwell, in which stair risers and treads are most often attached to squared faces cut into sloping stair stringers.

Interior wall coverings in light-frame construction typically include plaster-board, lath-and-plaster or decorative paneling.

Exterior finishes for walls and ceilings often include plywood or composite sheathing, brick or stone veneers, and various stucco finishes. Cavities between studs, usually placed 40-60 cm (16-24 inches) apart, are usually filled with insulation materials, such as fiberglass batting, or cellulose filling sometimes made of recycled newsprint treated with boron additives for fire prevention and vector control.

Roofs are usually build to provide a sloping surface intended to shed rain or snow, with slopes ranging from 1 cm of rise per 15 cm (less than an inch per linear foot) of rafter length, to steep slopes of more than 2 cm per cm (two feet per foot) of rafter length. A light-frame structure built mostly inside sloping walls comprising a roof is called an A-frame.

Roofs are most often covered with shingles made of asphalt, fiberglass and small gravel coating, but a wide range of materials are used. Molten tar is often used to waterproof flatter roofs, but newer materials include rubber or other synthetic materials. Steel panels are popular roof coverings in some areas, preferred for their durability. Slate or tile roofs offer more historic coverings for light-frame roofs.

Light-frame methods allow easy construction of unique roof designs. Hip roofs, which slope toward walls on all sides and are joined at hip rafters that span from corners to a ridge. Valleys are formed when two sloping roof sections drain toward each other. Dormers are small areas in which vertical walls interrupt a roof line, and which are topped off by slopes at usually right angles to a main roof section. Gables are formed when a length-wise section of sloping roof ends to form a triangular wall section. Clarestories are formed by an interruption along the slope of a roof where a short vertical wall connects it to another roof section. Flat roofs, which usually include at least a nominal slope to shed water, are often surrounded by parapet walls with openings to allow water to drain out. Sloping crickets are built into roofs to direct water away from areas of poor drainage, such as behind a chimney at the bottom of a sloping section.

Light-frame buildings are often erected on monolithic concrete slab foundations that serve both as a floor and as a support for the structure. Other light-frame buildings are built over a crawlspace or a basement, with wood or steel joists used to span between foundation walls, usually constructed of poured concrete or concrete blocks.

Various forms of trusses are also used to form floor structures, ceilings and roofs. Newer truss joist products often use laminated woods, most often chipped poplar wood, in panels as thin as 1 cm (3/8ths of an inch), glued between horizontally laminated members of less than 5 cm by 5 cm (two-by-two inches), to span distances of as much as 9 m (30 feet). Web trusses are often formed of 5 cm by 10 cm (two-by-four inch) wood members to provide support for roofing systems and ceiling finishes in place of joists and rafters.

Light-frame building methods allow architects to create designs resembling other construction methods, such as brick or stone veneer resembling structural brick or stucco resembling adobe.