Engineering

We are currently developing a project which specifies “Seismic Design Category C.” We are an East Coast truss manufacturer and have not encountered seismic requirements before.

We are concerned with SBCA’s BCSI-B1 Summary Sheet which under “Notes” makes a disclaimer. Our concern is if there would be an accident with our trusses and we point out that the bracing was not placed correctly according to SBCA documentation, which is sent with every job. If the accident goes to court, how will our attorney respond when the opposing attorney points out the disclaimer, which infers that the bracing we recommend must be flawed, otherwise it would not be disclaimed?

I almost always see wood trusses erected with no stability bracing at points of support. It seems to me that common sense and section 3.3.3.4 of The American Wood Council’s National Design Specification for Wood Construction (NDS) require that lateral support be provided at points of bearing. Plywood decking doesn't provide any more restraint for a wood truss than it does for a roof joist. I doubt if it was a concern with short span trusses having 4 in.

Are there any trusses that are supported strictly by the wood itself without any mechanical connections such as brackets?

It is critical that permanent top chord bracing is supplied by proper nailing of the valley truss bottom chords to the carrying truss top chords, through purlins or properly installed rated roof sheathing. If the sheathing is not carried through under the valley framing, then the permanent top chord bracing must be supplied in another manner.

Can a roof truss penetrate a one-hr. tenant separation wall without having a one-hr. rated ceiling? The building official insists that the 2x4 chords are combustible and nullify the integrity of the one-hr. rated partition that is constructed in an attic above an 8 in. C.M.U. bearing wall. The partition consists of gypsum board attached to 2 x 4 stud framing. The building official insists that a ledger must be attached through the gypsum board to support the trusses each side of the wall. This is almost saying that any rated assembly must have bearing only on other rated assemblies.

Our home has 2x4 roof trusses spanning 25 ft. spaced 16 in. O.C. Currently, there is limited attic storage on a plywood subfloor on the bottom chords, accessed via a small hatch in a closet. We would like to install a fold-down attic stair with a rough opening size of 25.5 in. x 54 in., with the long dimension perpendicular to the trusses. This would mean cutting the bottom chords of three trusses to frame the opening. Is this possible?

The Gypsum Association “Fire Resistance Design Manual” (GA-600-12) lists file RC2601 with two layers of 5/8 in. gypsum wallboard (GWB) on wood joists.

I need to obtain some information on fire-retardant-treated roof trusses.

I have just moved into a new home and during the construction I noticed that one of the trusses in the garage was damaged. The web plate had come off in two different locations. I notified the builder and they said they would take care of it. Approximately two weeks after I moved in, I noticed the ceiling in the garage started to sag, so I went into the space above the garage and found the truss was never repaired. I again notified the builder and they sent someone to fix it. I went and looked at the fix and this is where my question comes in.