Bottom Chord Dead Load
I have built a 30 ft. x 40 ft. pole barn with nine 30 ft. 2x4 7/12 pitch trusses that are 5 ft. O.C. I am planning to finish out the interior and will attach 7/16 x 4 x 8 OSB sheets to the trusses for my ceiling. Along with this, I will have to add several 2x4 nailers across the 30 ft. span between the trusses to attach the sheeting to. My question is: will these trusses have any problem supporting this ceiling? I am not planning on anything being placed in the section above the ceiling and there will be no walls or supports erected between the ceiling and the floor. The trusses came with data sheets that have a great deal of information but none of it directly answers my question. It does state that the truss ID is R01 and the loading is 20-4-10 60.00 in. O.C.
Contact the original truss designer that issued the truss design drawings for your R01 trusses.
The truss design drawing contains valuable information for anyone building with or inspecting trusses. 60.00 in. O.C. means that the trusses are designed to be spaced 60 inches on center (5 ft.). Every truss design drawing must specify the loads that have been accounted for in the design. In other words, the truss design drawing should tell you what the truss was designed for. 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). Now, the trusses themselves are going to be part of the TCDL and BCDL. However, just because the trusses were designed for some dead load, that does not necessarily mean the trusses can handle the additional load. You would need to add up ALL the dead load that will be applied to the bottom chord of this truss to determine if it is less than or equal to the 10 psf loading it was designed for. And since you stated that nothing will be placed in the section above the ceiling, meaning no Live Load will be added you don’t need to be concerned if the bottom chord can support any live load.