Kinds of Roof Trusses

Basic Truss Types

• There are two basic types of truss: pitched, or common, trusses and flat. All other truss types are variations or combinations of these basic trusses. A pitched or common truss is the most frequently used roof truss type. It gives a roof a pitched, or triangular shape. A flat truss is less expensive to construct than a common truss and is commonly used between stories to shape the ceiling of the lower floor and the floor of the upper story. A flat truss has a depth, in inches, equal to 7 percent of its total span, or length.

Common Trusses

• What a common truss is called is dependent on its span. A pitched truss that spans less than 16 feet is called a king post. A queen post, or fan truss, spans 10-22 feet. A fink, or W-truss, spans 16-33 feet. A Howe, or K-truss, spans 24-36 feet. A fan, or double fan truss, spans 30 to 36 feet. A modified queen, or multipanel, spans 32-44 feet. A double fink, or WW-truss, spans 40-60 feet. A modified, or triple, fan spans 40-60 feet. A triple fink, or WWW-truss, spans 54-80 feet. A Triple Howe, or KKK-truss, spans 54-80 feet. Scissor trusses are pitch trusses that have a raised triangular shape on both the bottom and top line of the truss, and are designed to shape cathedral ceilings.

One sided

• One sided trusses are half of a pitched truss, or a short flat truss designed to slope the roof in only one direction, rather than from a center peak. One sided truss types with a pitched design include a mono-scissor for raised ceilings, a common mono. Shortened flat trusses to create a one-directional slope include a sloping parallel chord truss, a sloping top chord truss and a slopping flat truss.

Other Special Trusses

• Several other trusses which are a specialized combinations of pitched and flat characteristics are used to meet special building needs. A room-in attic truss is braced to leave an open space in the center of the trusses in an attic. Bowstring trusses are used to support wide rounded roofs in structures like airplane hangers. A Gambrel roof or hip truss is used in barns and other large structures and gives old barns their distinctive silhouettes.