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Many
homes today have been built with trusses - prefabricated structural
assemblies that hold up the roof and the top floor ceilings. Trusses
are a series of triangles fastened together with gusset plates. The
outside members of a truss are called chords while the inner pieces
are known as webs.
Truss
uplift occurs when the top chord of the truss expands while the bottom
chord contracts due to changes in humidity. Truss uplift usually becomes
visible in a home during the winter when the bottom chords (the ceiling
joist part of the truss), which are buried under ceiling insulation,
stay warm and dry but the top chords are exposed to moisture. The
resulting stress causes the truss to lift up at its center. When this
happens, a crack can appear at the wall/ceiling juncture.
From
a structural standpoint, truss uplift isn’t a problem, but cosmetically,
it can cause cracks and separations in the drywall. Many homeowners
try to repair the cracks with drywall compound, only to have them
reappear next year.
Contractors
can mask truss uplift by securing the ceiling drywall to the top of
the interior walls and not the trusses for 18 inches away from the
interior walls. As the drywall flexes, it stays fastened to the walls
while the trusses lift above it.
Decorative
molding can also be installed where the walls meet the ceilings. The
molding should be fastened to the ceilings, not to the walls so as
the ceiling move up, so does the molding thereby hiding the gap. |
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