Live loads on roof trusses.
Roof truss bottom chord live load.
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.
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.
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.
Machine stress rated lumber msr lumber which has been individually tested.
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.
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.
Truss capacity is listed by pounds per square foot based on the following load rating criteria.
Live loadany temporary applied load to a floor truss chord.
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.
On the truss drawing will be a section which outlines all of the live and dead loads which the trusses are designed to support.
And wind loads per chapter 16 of this code.
I for sloping or flat roof with slopes up to and including 10 degrees.
2319 17 2 1 3 roof trusses shall be designed for a minimum live load of 30 psf 1436 pa a minimum dead load of 15 psf 718 pa on the top chord and a minimum dead load of 10 psf 479 pa on the bottom chord.
In other words the truss design drawing should tell you what the truss was designed for.
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.
Typically roof live load is snow while floor live loads are furniture human occupancy storage.
The live load shall be taken as follows.
