Roof Truss Bottom Chord Live Load

In floor truss applications 2x4 or 2x3 material is typically used with the wider portion of the board resting on the bearing or what is known as a 4x2 configuration.

Roof truss bottom chord live load. Truss capacity is listed by pounds per square foot based on the following load rating criteria. Live loads on roof trusses. 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. 20 4 10 means that the truss was designed for 20 psf top chord live load tcll 4 psf top chord dead load tcdl 0 psf bottom chord live load bcll and 10 psf bottom chord dead load bcdl.

On the truss drawing will be a section which outlines all of the live and dead loads which the trusses are designed to support. I for sloping or flat roof with slopes up to and including 10 degrees. Load bearing walla wall specifically designed to transfer a roof load and or upper floor load into the foundation. Live loadany temporary applied load to a floor truss chord.

Top chord live load snow and other temporary loads top chord dead load roofing materials weight of the truss itself other permanent items attached to the roof bottom chord live load storage and bottom chord dead load insulation ceiling. In other words the truss design drawing should tell you what the truss was designed for. A when access is provided 1500 n m 2 b when access is not provided 750 n m 2 except for maintenance ii sloping roof with slope greater than 10 degrees. Truss bottom chords shall be designed for a uniformly distributed concurrent live load of not less than 10 lb ft2 note that in footnote b the uninhabitable attics without storage have a 10 psf non concurrent live load while this same load in footnote g i e.

The live loads a truss is required to bear are determined by local building codes. Dead load weight of roof trusses top chord bottom chord webs weight per lineal foot plf 2x4 2x4 2x4 4 3 2x4 2x8 2x4 5 6 2x6 2x4 2x4 4 8 2x6 2x6 2x4 5 5 2x6 2x6 2x6 6 2 2x6 2x8 2x4 5 9 2x6 2x10 2x4 6 6 2x6 2x10 2x6 7 2 2x8 2x8 2x4 6 6 2x8 2x8 2x6 7 2 2x8 2x10 2x8 8 4 dead load weight of floor trusses depth in inches top chord bottom chord. In some cases a live load can be applied to a bottom chord either for storage purposes or if there will be movement within the truss such is the case in an attic truss. If the number next to bcdl bottom chord dead load is less than five psf pounds per square foot then the trusses and the building are not designed to support a ceiling.

Machine stress rated lumber msr lumber which has been individually tested. The live load shall be taken as follows. And wind loads per chapter 16 of this code.