Over the many years I’ve worked in the truss business, I’ve had the unfortunate experience of visiting numerous job sites where the trusses have collapsed. Without fail, every one of those collapses has been the direct result of improper bracing, improper hoisting, or a combination of both. In all but one case, the collapse occurred during construction. Fortunately, I have not been involved in any cases where there were fatalities, but there have been a number of people injured to varying extents.
There are great resources available that provide invaluable guidance on this topic, most notably is Building Component Safety Information – Guide to Good Practice for Handling, Installing, Restraining & Bracing of Metal Plate Connected Wood Trusses, or BCSI for short. There is no need for me to go into any great level of discussion about the contents of this guide, but I would say that if you are in the truss business and you are not familiar with the contents of BCSI, you should be. How can you expect your clients to properly install your product if you don’t fully understand the importance of proper handling and bracing yourself?
So rather than go over BCSI contents, I’m going to discuss a couple of common scenarios I have observed that led to trusses coming down. I should also say that every case of trusses collapsing I have witnessed involved longer span trusses, being used on either commercial or agricultural buildings. This is not to say that I think installers working on single family houses are necessarily doing a better job on following BCSI recommendations, I just believe that the factors leading to collapses are lessened by the nature of typical residential construction: relatively short spans, trusses in varying directions, shorter runs of the same truss. I also want to make it clear that I am not an engineer, and that you should seek advice from a professional engineer experienced in truss systems for further guidance.
If the jobs I observed had followed these common-sense recommendations, their outcomes would have been very different:
Use proper rigging during truss installation. In one case, 80’ trusses were being hoisted using two pick-up points running down from the crane line. The trusses in the air were bent easily 20’ out of plane. Of course, neither the lumber nor the plates are designed for this kind of stress. In this case, a truss snapped in half just before being set on the wall, and in doing so knocked all the other trusses over in domino fashion.
Use proper bracing. This can’t be over emphasized. Diagonal stability bracing needs to be provided in the plane of the roof, ceiling, and webs to keep the trusses from buckling prior to diaphragm installation. Installers often assume that the only bracing required is the continuous lateral bracing (CLB) shown on our truss designs. Worse, I have heard many truss company employees communicate the same to their clients. Any webs that need CLB also need diagonal bracing to tie the bracing to the ceiling and/or roof diaphragm. During construction of a new building for one of our lumber yard dealers, the trusses collapsed overnight during a small storm. Among other contributing factors was the complete absence of any diagonal or web bracing, and the presence of ~5’ long 1x4 “bracing” being used to brace the top chords of the 68’ span trusses.
Don’t rush the process. Several times I’ve seen cases where the installer is rushing to get the trusses up on the roof so they can send the crane away. I get it, crane time is expensive, and it can seem appealing to get the crane off the site as quickly as possible. But having this mindset leads to a greater likelihood that rigging, bracing, and other important items will be skipped. Encourage your clients to budget adequate crane time to allow safe truss installation. A thousand dollars of extra crane time is far less than the cost of new trusses, a fine from occupational health and safety, or most of all someone’s life.
Encourage your people to read BCSI so that they understand proper truss handling, installation, and bracing. They are your point of contact to your clients and the installers. Encourage your clients and their framers to do the same and encourage them to not only follow the guidelines but to seek assistance in advance if they have any questions.
Do you have other thoughts about how to prevent truss collapses? If so, please drop me a line.