Is There An Art To Building Trusses?
Building trusses isn't really an art form. Anyone knowing what a triangle looks like can build a simple truss, one that might even be aesthetically pleasing. You probably shouldn't stand under it though, especially if it's going to be supporting a load, like a roof. Rather than an art form, a truss falls into the category of engineering design. It is designed to be very strong and very stable, it is most often made of wood, though other materials can be used, and in home construction, the pieces of wood are held together by metal plates. Even the design of the metal plates is based upon engineering calculations, and the plates, as well as the entire truss, have to meet some rather strict standards.
One of the advantages of using trusses, is a house can be constructed which can have very large rooms. When trusses are not used, load bearing interior walls are required, making interior rooms generally smaller. With trusses, fewer load bearing interior walls are needed, and the only load bearing walls in many instances are the exterior walls.
Know What You're Getting Into - Just as the three-legged tripod is a very stable three-dimensional platform, the triangle shaped truss is a very stable two dimensional platform. A roof, or roof section, is supported by a set of parallel trusses, which when fastened to supporting structure and tied together by the roof planks, makes for an extremely strong and stable structure. As strong as the structure may be, building trusses involves more than simply building a triangle with some lumber, adding a few pieces of support, and hoping it will hold a roof up. Even for small jobs, one needs to look for a source of instruction on how to build a truss. These instructions need to be followed to the letter. A weak truss is a weak link, and if the same fault is build into all trusses, the final structure can be weak, unstable, or both.
Consider Prefabricated Trusses - If you're determined to build your own trusses, at the very least start with a small shed, perhaps graduating to a small garage, before taking on a house. Even then, the use of prefabricated trusses should be seriously considered. There are many businesses who specialize in building trusses. They will need to know the exact dimensions of the house, so that the proper size and configuration of each truss can be calculated. Many of these businesses use computer-driven saws to cut the lumber at precise lengths and angles. Connecting metal plates will also be selected or designed based on the dimensions of the trusses and the anticipated loads.
Many Factors To Consider - When the process of building trusses is completed, they will have to be kept out of the weather, and if they need to be stored, they need to be stored where the humidity can be kept fairly constant. This could be very difficult for the do-it-yourself builder to do, especially if a large number of trusses are going to be needed. Moist wood, or a warped truss can adversely affect the integrity of the entire structure. Even the type of lumber used needs to be taken into account. Southern pine is the lumber of choice by many for building trusses. The softwoods of the west coast are also very popular, but each wood type has its strengths and weaknesses, and these need to be understood and taken into account. Not only does the load which the roof will place on the trusses need to be calculated, but additional loading such as a snow load needs to be taken into account as well. Situations such as these must be considered and taken into account in the calculations used in designing and building trusses. As simple as the geometry appears, it is not a job for the amateur.