It’s a fact! Many roof structures fail during the construction process while others have taken years for an incident to occur. Buildings with proper design and construction of bracing systems are essential in reducing and/or eliminating wooden roof truss failures.
Residential and commercial roof trusses are made up of individual wood framing members connected with special metal plates. These trusses are amazingly strong once they’re installed as a system, but as individual trusses, they are surprisingly fragile and have very little lateral strength or resistance to lateral (wind) loading. Most truss failures are often attributed to improper or lack of temporary/permanent bracing, incorrect loading or overloading during construction, high winds during erection, utilizing weak members or bad joint connections, damaged, broken or improperly repaired trusses or installing unacceptable or unauthorized design changes in the field. These are the major reasons trusses fail and/or collapse.
Some key points to remember while investigating a truss collapse case:
- Truss erector is responsible for handling, installation and temporary bracing
- Truss erector must be familiar with installation practices as detailed in Building Component Safety Information (BCSI 1-03) – “Guide to Good Practice for Handling, Installing, Restraining and Bracing Metal Plate Connected Wood Trusses”, published by the Wood Truss Council of America (WTCA)
- Trusses over 60 feet are classified as long span trusses and The BCSI 1-03 suggests that these trusses be
designed by a Professional Engineer with temporary bracing experience
- Look for missing or misaligned metal plates (double plates required)
- Look for continuous lateral restraint (CLR) bracing of truss web members
- Look for “popped or pulled out” metal plates at joint connections
The failure to follow or observe these guiding principles has led to the collapse of many wood roof truss systems. Assessing a truss installer’s knowledge and experience greatly aids in determining a cause of the truss collapse. Section 802.10.4 of the 2006 International Residential Code (IRC) says: “Truss members shall not be cut, notched, drilled, spliced or otherwise altered in any way without the approval of a registered design professional.” In this case, they mean a registered engineer, and this includes repairing any damage.
So it’s important to provide proper bracing, both temporary and permanent, on installed sound, undamaged truss members and joint connections while following standard recommended installation procedures and if any alterations are required they must be designed and approved by a registered design professional.
Metal plated roof trusses, when handled, erected, and installed properly have proven their value within the building industry. However, their value is sometimes questioned when failures or collapses occur. In most of the case studies I’ve reviewed, the installation was usually not per the WTCA, or BCSI 1-03, and/or the “Truss Plate Institute” (TPI) (2003) recommended guidelines.
Allan Abbata is a senior consulting engineer at Warren and a licensed professional engineer in South Carolina, North Carolina, New York, New Jersey, Pennsylvania, Massachusetts, Missouri, Texas, Alabama, Maryland, Minnesota and Virginia. Allan holds a Bachelor of Science in Civil Engineering. He has more than 40 years of applied engineering expertise to include in-depth knowledge of building codes, rules and regulations that guide design. Allan has also prepared construction drawings and specifications, provided on-site supervision and inspection of construction projects, and has overseen project management and responsibility for overall performance of building contracts while also serving as the client’s liaison with local, state and federal agencies and municipalities.