Attic Truss Load Rating

The formula for truss loads states that the number of truss members plus three must equal the twice the number of nodes.

Attic truss load rating.

If the bottom chord of a roof truss functions as a floor joist such as in an attic room it carries a live load that also varies by use but a typical live floor load for a residential space is about 40 pounds per square foot. This truss load table guide illustrates how to read allowable load ratings for aluminum and steel truss. Safe load per table 4 1 specifies a 2000 lb over a 2 5ft x 2 5ft area. Both sides of the equation should be equal in order to end up with a stable and secure roof structure.

Keep in mind that these tables are for estimations only. This translates into a uniform load of 640 plf across 2 5 ft of the span. The live loads a truss is required to bear are determined by local building codes. Load rating chart ct290 load data ct290 truss sections are manufactured using 50mm 1 97 diameter x 2mm 08 wall main tube and 20mm 79 x 2mm 08 wall diagonal tube 6082 t6 aluminum alloy.

Is a safe estimate. Of stuff on it. The shapes and spans shown here represent only a fraction of the millions of designs produced by alpine engineers. Bcll 0 psf.

Live load psf roof type. The truss is analyzed for each possible location of the 640 plf load along the span. Alpine truss designs are engineered to meet specific span configuration and load conditions. The explanations below will help you determine the appropriate truss to use for your application or conditions based on allowable load ratings.

They have not been updated for the change in lumber values within the last decade. For trusses at 2 ft o c. Or the 25 psf snow load could be entered as a roof snow load with the unbalanced snow loading option turned off. The box truss is 290mm x 290mm 11 42 x 11 42 square.

If unbalanced snow loading isn t required or specified the truss designer may enter the 25 psf snow load as a top chord live load tcll set the load duration factor to 1 15 for snow and turn snow loading off completely. Total load psf duration factor. Included are a series of representative roof truss span tables that will give you an idea of the truss spans available for a particular load condition load duration lumber type and truss configuration. Bcll 0 psf no storage available in floor trusses.

So if your ceiling is unfinished you have some excess carrying capacity up there. If the number of members is labeled m and the number of nodes is labeled n this can be written as m 3 2 n.