A Truss Designer’s Opinion on Bracing – Part III
As a designer, you may ask yourself the following “Truss bracing…….is it really my responsibility?” Well, “YES!” Who else’s should it be? As a truss designer it is your responsibility. It may go without saying, but we as truss designers are responsible to provide a product that:
- Meets the requirements of the project
- Is cost-effective for the builder, manufacturer and owner
- Is safe for the erector
- Will stand the test of time
Trusses are designed to support building components both outside and in, from the material used on the roof to the mechanical accessories within the truss itself. Each of these components adds weight to the truss above and beyond the environmental weight applied like wind and rain and the erector standing on or within the truss. Each of these factors is taken into consideration while designing the truss. However, the truss has to be installed correctly in order for the collaboration to work. Wood transfers weight through the grain and plates from any point on the truss to the exterior wall. How smoothly that weight transfers depends on the design and the bracing. I have no doubt that each of us considers the project responsibilities, and the manufacturer responsibilities. The builder, owner and erector, I don’t know. At this point in time though, I would like to focus on the builder/erector responsibility we have. FACT: It is the truss designer who ensures that the roof system is designed in such a way that it is safe for the builder and erector. We see the stress points in the design and determine if “good enough” really is. Let’s face it, we as truss designer’s work in a perfect world. In the design software, all our walls are straight and uniform. FICTION: Everything truly is ”plumb and square” on the job site. That’s not the “real world!!!. No, in the real world there are a lot of factors that the truss designer never has to cope with. RESOLUTION: Fortunately, most experienced designers are aware of the ”fudge factor” and the good designers will plan for those types of contingencies. Problems are identified and solutions are built right into the truss ( a couple of extra inches here, a sixteenth inch short there) and the whole project runs smooth. Permanent bracing is no different. Designers spend a lot of extra time aligning webs in a fashion that allows for relatively easy installation of bracing, or modifying the type of bracing because there is no easy way to accomplish it. All this is in an effort to keep our counterparts in the field safe for the next project, and provide a quality project to the builder and home owner. Trusses are designed to stand up straight. Now that may seem like it goes without saying but there are minimal tolerances for how far out of plumb a truss can be based on the height. For instance a three-foot truss cannot be any more that 3/8” out of plumb. Fortunately, Simpson Strong-Tie has a valuable tool called the Wood Truss Restraint and Bracing Guide . TPIC also has the Handling, Erecting and Bracing of Wood Trusses. These are just 2 examples of several options available for proper erection and installation. Both will assist the Builder/Erector in the proper installation of wood trusses. It is the erectors “greatest” responsibility, even more important than attaching the truss to the wall, to verify that the truss is plumb and braced to within the tolerances provide. This ensures the entire system works as it was designed. Just one truss out of plumb could cause the entire system to break down! Just like the truss designer takes the extra time to align webs to help the erector with bracing, so the erector must take the extra time to ensure the trusses are plumb so they will perform their function as designed. What are your thoughts? You can read Part 1 of this series here. You can read Part 2 of this series here. Stay tuned for Part 4 in this series. Charles Burke – Design Professional Gould Design, Inc.