How Much Weight Will a Truss Roof Hold?

A Simple Explanation

• The amount of weight a truss holds depends upon its shape and strength. For instance, a truss with three sides of equal length exhibits a greater degree of structural integrity than a truss with two long, gradually sloping sides and one very long hypotenuse. The strength of the material used also affects the load bearing capacity; steel supports larger loads than wood, and heavy woods support more weight than soft. A truss’ actual maximum weight capacity can range from a few hundred pounds to upward of 10,000.

A Complex Explanation

• In “Load Bearing Capacity for Roof Trusses,” John Dalsgaard Sorensen identifies key factors in load bearing capacity as the length truss sides, the modulus of elasticity -- how much give the material has -- and the bending, compression and tension strength of the material. Each of these gets a different rating. When taken together, these ratings give a basic idea of a truss' load bearing capacity. The direction of weight always plays a factor. A triangular truss can increase load-bearing capacity by using interior triangles to direct weight to points designed to carry high loads.

Weight Distribution

• The weight distribution network connected to a truss affects load bearing capacity. For instance, a truss connected to a basic wood frame wall directs weight to that wall, though must support a significant amount of weight itself. A truss connected to a complex weight distribution system, such as a stub truss connected to steel or concrete walls, can support significantly more weight by placing more stress on the walls. However, the truss must support and distribute weight. A truss made of weak wood will break under heavy loads, even if connected to a strong support and distribution network.

Design for Support

• Skilled architects, engineers and builders always design roof trusses to meet the needs of a building and its area. For instance, a contractor in an area with heavy snowfall will install a truss system capable of handling the weight of snow. Always contact a specialist to find out the exact load bearing capacity of your roof or if you need to know whether you can place additions on or walk across a roof. Determining actual load bearing capacity requires too complex a process for the layperson, and safety always comes first.