Chris Lewis wrote:

I don't really remember the details very well. The issue revolves around
the fact that the bottom chord of a truss _may_ want to lift off
interior partitions. I think in some cases, you can simply fasten the
chord down hard to the top plate, perhaps with joist hangers. Others
revolve around techniques on how to dry wall the wall-ceiling joint.

And there's always crown moldings ;-)

The problem is called "Truss Uplift" and is mainly a concern in colder
climates. What happens is that during the winter, the bottom chord remains
relatively warm as it is burried in insulation (e.g.: the trusses in our
house have bottom chords mainly made of 2x5 stock - yes two by five - while
the insulation is at least 14" deep).

The other members of the trusses are up in the cold and they tend to
contract in the cold. This contraction has an upward force on the bottom
chord. This can lift the bottom chord, and your ceiling, away from
partition walls.

Our partitions are framed with steel and were done AFTER the roof was in
place. For steel, the top chanel is attached to the ceiling structure,
which was a concern for the second floor as the trusses span the entire 33'
width of the house. Our method was to use two channels: one attached to
the bottom of the chord, and the other attached to the studs. The stud
channel was inserted into the truss-attached channel. This provides lateral
support while allowing truss lift to not damage the steel stud walls.

This does not prevent any gapping of the drywall between the ceiling and
the walls, but after three winters we have no visible cracking in those
joints. I suppose our trusses have been designed to minimize uplift.

--
Calvin Henry-Cotnam
"I really think Canada should get over to Iraq as quickly as possible"
- Paul Martin - April 30, 2003
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