Expert: Dave Johnson - 1/21/2008

Question
I live in a new house and need some more space. The garage is about 24 feet deep with Queen Post trusses.  The roof pitch is either 10/12 or 12/12.  I would like to change the trusses to a room-in-attic style.  I would also need to add floor joists as the current truss chords are only 2x4 and are 24" apart.  I've read enough to know that I can change the design of the truss, but how do I add the new floor joists?  Would I fasten them to the current truss chord?  Would I align the top of the new floor joist with the top of the truss chord?  If I do this then I would need to add bracing to the walls as the bottom of the floor joist would be below the top of the wall.  Is it better to align the bottom of the new joist with the bottom of the existing truss chord and then set the new joists on the top of the walls?  Where can I find charts to determine maximum joist spans?

Thanks,
Dan

Answer
Hi Dan,
Yes, you would sister them to the existing bottom chord and they would be flush with the BOTTOM of the chord.
They also need to be bearing on the walls, not just attached to trusses.
Go to "american wood council span tables" they will have all the info you need.
best of luck,
Dave