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Vocabulary of Trusses

Bearing A structural support, usually a beam or a wall that is designed by the building designer to carry the truss reaction loads to the foundation.

Bottom Chord A horizontal or inclined member that establishes the bottom member of a truss.

Bottom Chord Bearing Term used to describe the bearing condition of a parallel chord truss that bears on its bottom chord.

Bridging Wood or metal members that are placed between trusses and joists in an angled position intended to spread loads.

Butt Cut Slight vertical cut at outside edge of truss bottom chord to ensure uniform nominal span and tight joints. Truss industry for standard heel, but cut equals 1/4".

Cantilever The part of a truss that extends beyond its support, exclusive of its overhang. Note: the overall span of the truss is to include length of cantilever.
Ex: 28' truss with 2' cantilever equals a truss with a 2' cantilever and the distance between two outside bearings equals 26'.

Clear Span (Clear opening) Generally indicates the inside or interior frame to frame dimensions.

Clipped Truss Truss that has been stubbed from one or both ends.

Concentrated Load Super-imposed load centered at a given point.
Ex: Girder to girder connection, HVAC units.

Cricket A ridge or drainage diverting roof framing - commonly found on the high slope of a chimney.

Dead Load Any permanent load such as the weight of roofing, flooring, sheathing, insulation, or ceiling material, as well as the weight of the truss itself.

Deflection Downward vertical movement of a truss (when in place) due to live and dead loads.

Design Loads The dead and live loads which a truss is engineered to support.

Fascia The flat surface located at the outer end of a roof overhang or cantilever end.

Gable Truss A non-structural member which is manufactured to match the profile of another truss. This type of frame requires continuous support by a bearing member. A structural gable is possible by adding studding between the webbing of a common type truss.

Gambrel A roof profile having two slopes on each side. The lower slope is usually steeper than the upper one.

Girder Truss A truss designed to carry heavy loads from other structural members framing into it. This is usually, but not always, a multi-ply truss.

Header A conventionally framed wood girder located between stud, joist, or truss opening.

Heel Point on a truss at which the top and bottom chords intersect.

Interior Bearing Term used to describe supports which are interior to two exterior supports.

Lateral Bracing Members placed and connected at right angles to a compression web member of a truss. Usually denoted on truss engineered drawings as .

Live Load Any load that is not permanent.
Ex: Snow, people, and furniture.

MSR Machine Stress Rated Lumber: Lumber that is given a strength value through mechanical evaluation.

Nominal Span Outside to outside horizontal measurement of bottom chord of truss. This measurement is to include cantilever if present. Also referred to as overall span.

Overhang The extension of the top chord of a truss beyond the outside of the bearing support or the bottom chord.

Overhang Assembly Attachment to heel of truss to add overhang to a truss. This is common where the overhang must be left off for shipping purposes.

Panel Point The location on a truss where the web members intersect the top and bottom chord.

Partition Separation Per the Wood Truss Council of America, "partition separation is cracking that develops between interior partition walls and ceiling or floor finishes, usually characterized by gaps that open in the winter and close in the summer." For causes, prevention, and solutions to this problem, click here to view a report (pdf format) put out by the Wood Truss Council of America.

Peak Point on the truss where the sloped chords meet.

Piggy-Back Truss A truss made in two pieces usually consisting of a step-type truss with a triangular cap fastened to it. Trusses are generally formed this way to stay within D.O.T. width requirements.

Pitch The incline angle of the roof. Described as the ratio of total rise over the total width or run.

Plumb Cut Top chord end cut to provide for the vertical installation of the fascia.

Ply One member of a multi-member truss or beam.

Purlin A horizontal member attached to and placed perpendicular to the truss top chord to support the roofing.

Ridge The horizontal line made by the top of the two sloping surfaces.

Scab Additional lumber connected to a truss to effect a splice, extension, or general reinforcement. Commonly used in field repairs.

Setback The distance from the outside edge of the wall to the face of a girder.

Shop Drawings Detailed drawings of a truss showing critical dimensions such as span, overhang, cantilever, slope, etc.

Slope The incline angle of the roof described in inches of rise per one foot of run.

Soffit The underside of a roof overhang or truss cantilever end.

Spacing Centerline distance between trusses - normally 24" O.C. (on center).

Span Term used to communicate out to out span, or overall span of truss to include cantilever end.

Strong Back Two inch dimensional framing member attached perpendicular to floor trusses. Often through the chase opening and placed vertically against the web.

T-Brace A brace consisting of two inch dimensional lumber nailed directly to the web member requiring lateral or extra bracing.

Tie-In The total length between girder and next bearing point.

Top Chord Bearing The bearing condition of a parallel chord truss that bears on its top chord extension. This can also apply to a sloping chord truss.

Top Chord An inclined or horizontal member that establishes the top member of a truss.

Truss An engineered structural component assembled from wood members, metal connector plates and other mechanical fasteners. Designed to carry its own weight and superimposed design loads. The truss members form a semi-rigid structural framework and are assembled such that the members form triangles.

Valley Truss Not a truss, but traditionally called so. A set of triangular components used to frame the shape of dormers and to complete roof framing where trusses intersect at perpendicular corners.


	Wheeler Truss and Building Products Divisions Home Page: http://www.wheeler-con.com/truss/index.html Last Modified 7/6/06

Rock Island, Illinois: Sales Contact: Curt Degner Phone: (309) 787-1729 or 800-322-0505 Fax: (309) 787-8307 Email: cdegner@wheeler-con.com 8109 29th Street West Rock Island, IL 61201	West Des Moines, Iowa: Truss Systems Contact: Scott Easter Phone: (515) 224-1909 or 800-369-8787 Fax: (515) 223-0076 Email: seaster@wheeler-con.com Wholesale Building Products Contact: Joe Streck Phone: (515) 224-1900 or 800-369-2450 Fax: (515) 223-7813 Email: jstreck@wheeler-con.com 1100 Hoak Drive, West Des Moines, IA 50265	Waverly, Kansas: Contact: Nick Bailey Phone: (785) 733-2848 or 800-524-3246 Fax: (785) 733-2850 Email: nbailey@wheeler-con.com 1959 Old Highway 50 Waverly, KS 66871

Vocabulary of Trusses

Bearing		A structural support, usually a beam or a wall that is designed by the building designer to carry the truss reaction loads to the foundation.
Bottom Chord		A horizontal or inclined member that establishes the bottom member of a truss.
Bottom Chord Bearing		Term used to describe the bearing condition of a parallel chord truss that bears on its bottom chord.
Bridging		Wood or metal members that are placed between trusses and joists in an angled position intended to spread loads.
Butt Cut		Slight vertical cut at outside edge of truss bottom chord to ensure uniform nominal span and tight joints. Truss industry for standard heel, but cut equals 1/4".
Cantilever		The part of a truss that extends beyond its support, exclusive of its overhang. Note: the overall span of the truss is to include length of cantilever. Ex: 28' truss with 2' cantilever equals a truss with a 2' cantilever and the distance between two outside bearings equals 26'.

Clear Span		(Clear opening) Generally indicates the inside or interior frame to frame dimensions.
Clipped Truss		Truss that has been stubbed from one or both ends.

Concentrated Load		Super-imposed load centered at a given point. Ex: Girder to girder connection, HVAC units.
Cricket		A ridge or drainage diverting roof framing - commonly found on the high slope of a chimney.
Dead Load		Any permanent load such as the weight of roofing, flooring, sheathing, insulation, or ceiling material, as well as the weight of the truss itself.
Deflection		Downward vertical movement of a truss (when in place) due to live and dead loads.
Design Loads		The dead and live loads which a truss is engineered to support.
Fascia		The flat surface located at the outer end of a roof overhang or cantilever end.
Gable Truss		A non-structural member which is manufactured to match the profile of another truss. This type of frame requires continuous support by a bearing member. A structural gable is possible by adding studding between the webbing of a common type truss.
Gambrel		A roof profile having two slopes on each side. The lower slope is usually steeper than the upper one.

Girder Truss		A truss designed to carry heavy loads from other structural members framing into it. This is usually, but not always, a multi-ply truss.
Header		A conventionally framed wood girder located between stud, joist, or truss opening.
Heel		Point on a truss at which the top and bottom chords intersect.

Interior Bearing		Term used to describe supports which are interior to two exterior supports.
Lateral Bracing		Members placed and connected at right angles to a compression web member of a truss. Usually denoted on truss engineered drawings as .

Live Load		Any load that is not permanent. Ex: Snow, people, and furniture.
MSR		Machine Stress Rated Lumber: Lumber that is given a strength value through mechanical evaluation.
Nominal Span		Outside to outside horizontal measurement of bottom chord of truss. This measurement is to include cantilever if present. Also referred to as overall span.
Overhang		The extension of the top chord of a truss beyond the outside of the bearing support or the bottom chord.
Overhang Assembly		Attachment to heel of truss to add overhang to a truss. This is common where the overhang must be left off for shipping purposes.

Panel Point		The location on a truss where the web members intersect the top and bottom chord.
Partition Separation		Per the Wood Truss Council of America, "partition separation is cracking that develops between interior partition walls and ceiling or floor finishes, usually characterized by gaps that open in the winter and close in the summer." For causes, prevention, and solutions to this problem, click here to view a report (pdf format) put out by the Wood Truss Council of America.
Peak		Point on the truss where the sloped chords meet.
Piggy-Back Truss		A truss made in two pieces usually consisting of a step-type truss with a triangular cap fastened to it. Trusses are generally formed this way to stay within D.O.T. width requirements.
Pitch		The incline angle of the roof. Described as the ratio of total rise over the total width or run.
Plumb Cut		Top chord end cut to provide for the vertical installation of the fascia.
Ply		One member of a multi-member truss or beam.
Purlin		A horizontal member attached to and placed perpendicular to the truss top chord to support the roofing.
Ridge		The horizontal line made by the top of the two sloping surfaces.
Scab		Additional lumber connected to a truss to effect a splice, extension, or general reinforcement. Commonly used in field repairs.
Setback		The distance from the outside edge of the wall to the face of a girder.
Shop Drawings		Detailed drawings of a truss showing critical dimensions such as span, overhang, cantilever, slope, etc.
Slope		The incline angle of the roof described in inches of rise per one foot of run.
Soffit		The underside of a roof overhang or truss cantilever end.
Spacing		Centerline distance between trusses - normally 24" O.C. (on center).
Span		Term used to communicate out to out span, or overall span of truss to include cantilever end.
Strong Back		Two inch dimensional framing member attached perpendicular to floor trusses. Often through the chase opening and placed vertically against the web.

T-Brace		A brace consisting of two inch dimensional lumber nailed directly to the web member requiring lateral or extra bracing.

Tie-In		The total length between girder and next bearing point.
Top Chord Bearing		The bearing condition of a parallel chord truss that bears on its top chord extension. This can also apply to a sloping chord truss.
Top Chord		An inclined or horizontal member that establishes the top member of a truss.
Truss		An engineered structural component assembled from wood members, metal connector plates and other mechanical fasteners. Designed to carry its own weight and superimposed design loads. The truss members form a semi-rigid structural framework and are assembled such that the members form triangles.
Valley Truss		Not a truss, but traditionally called so. A set of triangular components used to frame the shape of dormers and to complete roof framing where trusses intersect at perpendicular corners.