When designing trussed rafters, because there are three different types of loads that affect the rafters, the weight needed to support the loads must always be taken into consideration. The building codes of the area in which the trusses will be installed must also be followed, so knowing the code before beginning a plan is suggested by the Structural Building Components Association in order to avoid any setbacks when building.
Three different types of weight loads will act heavily upon the structure, so the trussed rafters must be designed to accommodate these loads. The first is the live load, which includes the occupants and moveable objects in or on the structure. The next load is called the dead load, which is the weight of the building materials and the structure itself. The last is the environmental load, which includes weight created by snow, wind and earthquakes or other weather- and environment-affected weight that can cause strain on the structure.
It is the job of the building designer to know the truss codes and the weight factors and to be able to design the structure accordingly. Resources such as the AWC Wind Guide, SBCA Load Guide and the International Building Code are available for guides when coming up with a design.