Roof trusses are engineered components. When damaged or altered this can effect structural integrity of the roof system. Localized damage to one or two trusses will typically not result in structural failure of the roof system, but could cause the roof or ceiling to sag. In residential construction this can also be a problem when selling a house because home inspectors often find damaged or roof trusses.
Because trusses are engineered components, typical building codes specify that repairs or alterations must be designed by a registered design professional. In most cases that would be a Licensed Professional Engineer with experience in designing repairs or alterations to trusses.
Typical wood roof trusses consists of numbers members-called chords and webs-that are connected together with metal plates. Relatively small metal teeth protrude from the plates and the plates are pressed into the wood members using thousands of pounds of force for each joint. It is tempting to look at these plates and assume that a few nails would do the same job, but that is not the case. It takes many nails to equal the capacity of a typical connector plate. When using nails to joint truss members it is also necessary to use lumber, plywood, or Oriented Strand Board (OSB) to join the members. Sometimes structural screws are also used for truss repairs. For typical roof trusses used in light frame construction bolts are usually not used because of spacing requirements. Even when nails or structural screws are used spacing must be considered and the fasteners used at the repaired joint or member extend much further from the joint or crack than a metal connector plate.
We have designed repairs for many roof trusses. We also have the capability to perform truss repairs. Sometimes it is more cost effective or expedient for BCI to design, perform, and certify the repairs instead of designing the repairs, producing the necessary documentation to provide to a contractor, and then inspect the repairs. It is not uncommon for contractors to overlook necessary requirements. It is also sometimes difficult to correct improperly performed repairs.
Due to changes in wood moisture content or improper handing of trusses metal connector plates sometimes separate from the wood members.
Metal connector plates can sometimes be pressed back when the teeth are still in alignment with the original holes. However, this is often not a simple process.
For truss repairs to be effective the gusset plates must be in contact with the wood members and the nails must extend through all members. These are some examples of truss repairs performed by carpenters who were given detailed drawings to follow. These repairs are not acceptable.
This truss web member cracked due to defective lumber
These are examples of proper truss repairs using gusset plates