The repair and modification of metal plate connected wood trusses can be a very complicated subject, because each situation must be analyzed individually. Common situations that require repairs include: damage to the truss from storage and delivery, handling, installation, adverse environments, fire, and manufacturing mistakes. Whatever the reason for a repair, the principles followed by the Truss Designer are similar. The truss repair must result in a truss that is able to carry all loads intended for the truss.  This guide will cover the key concepts involved with a truss repair.




  • Trusses are typically designed for a specific application.
  • Therefore, truss repairs or modifications must be analyzed on a case by case basis.
  • The repair designer needs to be provided with accurate information.
    • In simple scenarios, a “marked-up” Truss Design Drawing (TDD) or photos of the damaged truss may be sufficient.
    • In more complex situations, a jobsite visit may be required.
  • What is the difference between a Repair and a Modification?
    • Truss Repair (top): restoring a truss back to its original shape and strength in situations where damage has caused a change or a reduction in either.
    • Truss Modification (bottom): altering a truss profile, loading, and/or bearing conditions to fit a situation for which the original truss was not designed.

  • The truss repair or modification must result in a truss that is able to safely carry all intended loads.
  • This presentation will provide a step by step approach to truss repair
  • Depending on the extent of damage, some trusses cannot be repaired and must be replaced.
  • BCSI-B5 recommends the following steps to correct damage, jobsite modifications or installation errors.

Step 1

Temporary Bracing

If the truss is installed, temporarily brace or support the truss to prevent further damage to the truss and danger to the workers.

Step 2

Report Damage

Report damage, alterations or installation errors to the truss manufacturer immediately.

Provide the original as-built TDD (if available) to the Truss Repair Engineer along with any materials describing the repair needed

  • If the TDD is not available, provide a sketch of the existing truss, showing:
    • Geometry (dimensions)
    • Materials (size, species, and grades)
    • Size and type of connector plates

  • The following can be helpful in conveying the repair condition:
    • Redline of TDD
    • Photos of the damaged truss
    • Layout of the building
    • Additional written explanation about the damage
    • A jobsite visit may be required in more complex situations

  • Is the lumber damaged? If so provide:
    • Exact location of damage from a known location such as a panel point or bearing
    • Description of damage
    • Dimensions of the damaged area
    • Note any treatments applied to the lumber (weather or fire resistance)

  • Are plates or joints damaged? If so provide:
    • Location or the Truss Design Drawing joint number of the damaged plate or joint
    • Size of the damaged plate
    • Description of plate or joint damage
    • Indicate if there is damage to one or both faces of the plate/joint

  • Load types and locations supported by the damaged truss
    • Supported trusses may need to be cut back to fit repair
  • Any loading changed from the original TDD
  • Total number of plys and how many are damaged

  • Notify the Truss Repair Engineer about:
    • Stage of construction
      • If the truss has been set
      • If sheathing has been applied
    • Any interference that may affect the repair
      • HVAC
      • Electrical
      • Plumbing

  • Notify the Truss Repair Engineer about:
    • Preferred materials for the repair
    • Tools and materials available at the jobsite
      • Sheathing and lumber typical sizes and grades
      • If there is a plate press
    • Availability of special order materials
    • Additional considerations

Step 3

Obtain Repair Drawing

  • DO NOT begin a repair without a Truss Repair Design Drawing (TRDD)
  • Upon receiving the TRDD, check to make sure the repair can be made.
  • If the designed repair cannot be accomplished, inform the building designer, truss designer, or truss manufacturer.
  • If conditions have changed at the jobsite, notify the Truss Repair Engineer to obtain an updated repair detail.

Step 4

Pre-Repair Setup

  • Prior to beginning the repair, lay the truss flat on a solid, level surface.
  • If the truss is already installed, shore up the truss to relieve any load.

Step 5

Perform the Repair

  • Repair the truss by following the information provided in the TRDD exactly.
    • All materials are the same size, grade, species as specified (or better)
    • Materials are cut to proper dimensions and placed in correct orientation
    • All fasteners are sized and spaced as described
    • Nails are clinched if required
    • If specified, the repair extends a certain length beyond the damage

Step 6

Inspect the Repair

  • Make sure that both the damage condition and repair are as described in the repair drawing
  • Consult the Truss Repair Engineer if there are any differences between the drawing and what was done in the field

Step 7

Keep Records

  • Keep the TRDD in case the building official, building designer or owner requests it.