Partition Wall Attachment To Bottom Chords
I am remodeling a 16-year-old ranch style home. The roof consists of 4/12 26 ft. span trusses, 24 in. O.C., over 2x4 stud walls. What is the recommended means of affixing the top plate of new interior partitions to provide the lateral support needed for the partition? Also, I want to hang a soffit above and overhanging the new kitchen cabinets (recessed lighting placed within). What is the recommended means of attaching the soffit to the underside of the trusses so as not to interfere with the designed movement of the trusses under the variable live load experienced (snow load)?
As far as the truss is concerned, it does not need to be attached to the wall assuming it was designed to clear span the full 26 feet. However, as you implied, the wall needs to be connected to the truss for the wall's stability. One method to do this and still allow for vertical movement of the truss is to use slotted anchors at the top of the partition wall.
The soffit attachment to the ceiling is out of the scope of our expertise. One thing to keep in mind though, is that the expected deflection for a fairly short span truss, like 26', is not as much as you might think. Even under full design loading (which the truss probably hardly ever experiences) these flat bottom chord trusses can deflect less than 3/8 in. at the center of the span.
For additional information, see SBCA’s CTB – Drywall Cracking & Crowning Issues.