A truss is a series of framing members that create the roof structure of a building. When looking at garage plans, many customers wonder if they can build their own trusses as a way to save money. The short answer is no. A truss must be engineered by its manufacturer for the customer’s project. This is due to code compliance issues. Here is some information about trusses and why they need to be code compliant.
Trusses in the IRC
Years ago, engineers designed trusses. They put them in carpentry, building and technology books for others to reference. In practice, someone chose their span, spacing, loads applied, and the roof slope/profile, and then built their trusses on site. As the years went on, liability became a concern. The building codes required engineering and certification of every truss. This was done by a state licensed professional engineer or architect.
At Behm Design, each plan is compliant with the IRC (International Residential Code) using the prescriptive approach. The code says that conventional framing and other methods of construction must be fully tested by a testing facility. The prescriptive approach allows for building walls, floors and roof/ceiling structures. Roof framing such as rafters and joists are considered a simple span in regards to load tables/grades/species. With the prescriptive approach, each span uniformly distributes loads allowing homeowners to select framing without having them engineered. Trusses, on the other hand, do not have a simple span and thus need to be made by a truss manufacturer who is licensed in your state.
Trusses Must Be Engineered
A truss presents a unique situation. Instead of being a simple span like the framing mentioned above, a truss is a network of wood or metal pieces that work together to resist the load in the span. The truss needs to be completely engineered in order to analyze all the forces in the network. The engineering ensures that forces of equilibrium are resolved and that the truss is safe to carry applied loads. It is not legal to pre-engineer trusses on stock plans to be used in unknown locations. Every truss manufacturer in the United States is licensed in their state for truss design, fabrication, and certification.
While building your own truss on your new garage seems like a good idea, remember the IRC has very specific rules. However, the point of the rules is to make these structures safe for homeowners. At Behm Design, our garage plans include space for manufactured trusses. Once you order your plans, do some research about truss manufacturers in your state and then build the garage of your dreams! Contact Behm Design for more information about trusses and their compliance with IRC.