Last month’s article, Preventing Truss Collapses, talks about some of the job site mistakes that can lead to truss collapses. I have no scientific data to back this up, but it is my belief that all truss collapses could be prevented by following proper lifting methods and bracing of the trusses during installation. However, I think it is also true that there are some things that truss companies and truss designers can do to help reduce the risk of collapse.
Before I proceed, I will acknowledge that most, if not all, of the following suggestions will result in slightly higher truss supply costs. In my experience, it is rare to encounter the builder who is willing to consider the site savings that can result. As we all know, most builders are in the habit of comparing just the bottom-line cost on your truss quote to one from your competition. It can be a tough task to convince your customer that it is in their best interest to give you more money than your competition, but it still merits having the conversation.
Here are some simple suggestions that may help your clients install trusses easier, and maybe save some money in the long run.
- Where possible, line up as many webs as possible in adjoining trusses. In most truss software, the default is for the software to look at a chord segment, and divide that into panels less than some maximum. As the span changes from one truss to the next – such as in the case of a stub truss – the software just looks at each bottom chord segment and assigns panel points accordingly. By maintaining as much of the web pattern from one design to the next as possible, it is much more likely that the framer will be able to do a proper job of bracing. As a side benefit, you may see some savings in setup time from one truss to the next, especially if you don’t have an auto-jig table.
- Reduce or eliminate long compression webs. Flipping the direction of long compression webs will usually result in those members being in tension, and adjoining shorter webs being in compression. Shorter compression webs will generally need less bracing. In the truss plant, savings can occur when you reduce the length of long compression webs that may need to be 2x6 or 2x8 material, but when flipped become 2x4 tension webs.
- This one can be a little harder to implement, but can be a big help in some hip end systems. Typically, in a stepdown hip system, there are few or possibly no webs that line up from one hip truss to the next as the pitch break geometry changes. On each individual truss, it is usually possible to deal with compression webs needing bracing by substituting a “T” or “I” brace, but that doesn’t help to deal with overall stability. Creating a vertical web at one or more fixed locations along the span can provide a location for the installer to add some X-bracing that will serve to stabilize the roof. Mid-span is generally an easy location to do this, but in long span trusses it might be desirable to have vertical webs in fixed locations every 20’ or so.
Do you have other tips to share that help with installation and bracing? If so, please pass them along, I’d love to hear from you.