huangyhg

nagging open web roof truss/ sheet rock question
i just started work on this ongoing project, and my job is to install simpson dtc strut clips to attach the non-bearing interior walls to the open web roof truss, keeping the two nails on the roof strut part of the clip with 1/16" of wiggle room to allow deflection of up to 3/4" in the roof truss.
i know that we plan to hang the sheetrock directly on to the bottom chord of the roof truss. my nagging question is: how will the sheetrock joints not crack when the roof truss deflects up to 3/4"?
james,
the drywall contractor will need to made aware of the 3/4" deflection so that he/she can install expansion joints between the gypsum panels.
thanks for the great fast response. i'm thinking of 3/4" expansion joint around perimeter of ceilings.

ok - apparently you are concerned about the non-bearing endwalls that are parallel with the truss span. correct?
three things...
1. 3/4" seems like a lot to me. i would normally expect something in the order of 1/4" max.
2. normally this is taken care of by installing the gyp on the walls first and the lid last. that way the ceiling gup can slide up and down over the wall gyp.
to minimize the deflection at this wall, could you double up the last two or three trusses to cut down on the deflection to an acceptible range? maybe even triple the truss closest to the wall, then double, then single, to taper out the deflection so that ist is not so easily read.
i can see where this would be a definite problem for a 3/4" deflection.
mike mccann
mmc engineering
i think tpi - truss plate institute has a diagram showing how to handle this. check them out or the local truss supplier.

the problem seems to be a little more complicated than i first described:
big house, built over puget sound, on a steel frame.
there are few interior load bearing walls: around the perimeter of an elevator, two stairways, some skylights. the roof in question is flat, about 80 feet by 50 feet. most of the roof is open web roof truss, but there are at least three sections where the roof support is either lvl or gluelam. these different roof systems do not align with different rooms below. (maybe they used to, the design seems to change daily) so some ceilings will have to transition from a gluelam to a lvl to a open web roof truss. the engineer says the open web roof truss will deflect up to 3/4" in snow load. the others won't.
we've built all the nonloadbearing interior walls to handle the deflection. but the ceiling...what to do about that, other than put in a bunch of giant expansion joints? the boss wants to now hang each ceiling in each room by wires. but that doesn't seem to solve the problem. springs, maybe.

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