Truss Installation Guide

These recommendations originate from the collective experience of leading technical personnel in the wood truss industry but must, due to the nature of responsibilities involved, be considered only as a guide for the use of a qualified building designer, builder or erection contractor. Buildbase Limited expressly disclaims any responsibility for damages arising from the use, application, or reliance on the recommendations and information contained herein by building designers or by erection contractors.

  • Truss support diagramMark the bearing plates on both walls to the required spacing of trusses, normally 24” on centre.
  • Hoist the trusses to the roof level, taking care not to bend or twist the trusses.
  • If interior walls are available, trusses may be laid flat.
  • If no partitions exist, trusses shorter than 32’ may be inverted and hung from the bearing plates.
  • Erect Gable or End trusses and install braces to prevent lateral movement (See Figure below).
  • Run a string from heel to heel of the end trusses to be used as a guide line.
  • Erect trusses using string to locate heels. Brace each truss as it is erected.
  • Trusses may be marked at one end. Place trusses so that all marked ends are on the same side of the building.
  • When flat trusses are used, ensure that they are installed with the proper side up.
  • Install temporary bracing with sufficient cross bracing to prevent trusses from buckling or toppling over. Install permanent bracing.
  • Complete roof by installing roof decking, gable end ladders, etc.

Truss StrengthTrusses must be in the vertical plane to take advantage of their superior ability to support loads. The truss erector or the builder must take the necessary precautions to ensure that erection procedures and handling methods do not damage the trusses and thus reduce their load carrying capacity.

Truss Alignment

ALL TRUSSES ARE LATERALLY UNSTABLE until properly braced. The longer the span the more care required. Adequate restraint is necessary at all stages of construction. Complete stability is not achieved until the bracing and decking is completely installed and properly fastened.

Erection, bracing, and procedures as well as the safety of the workers are the responsibility of the erector.

Problems may occur in attempts to realign trusses. Align each truss and place it permanently in position before it is connected to the bracing system. Once there is a load, even from the weight of the truss itself, large lateral forces are developed by attempts to realign the trusses. This may break the bracing system.

When properly aligned, each top chord should not vary more than 1/2 inch from a straight line.

Out-of-plumb installation tolerances

Truss Vertical Alignment Truss Bracing

The bracing system should provide support at spacings at no farther apart than the drawings show for the bridging. Without proper bracing trusses may not support even their own weight. 

Collapse can easily occur without a bracing system that will prevent both horizontal sway or roll over. By rolling on their sides, where they have no strength, the trusses will break or pull the ends off the bearings.

Truss Collapse

 

DO NOT permit cutting, drilling or any procedure that may damage the chords or webs.

DO NOT remove webs (even temporarily).

DO NOT make field repairs to damaged trusses without the approval of the manufacturer.

DO NOT overload single or groups of trusses with plywood, roofing or other construction materials or tools.

DO NOT erect damaged trusses. Should a truss or group of trusses fall to the ground or be damaged in any way at all, do not proceed! The site engineer of note must certify that the trusses are satisfactory to erect. Notify the truss supplier immediately.

Temporary Bracing

Flat Truss Temporary Bracing Truss Top Chord Bracing

We acknowledge the kind permission of Roof Trusses & Components Ltd, Ontario, Canada for the use of some of their copyrighted illustrations and texts.

 

 

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