A.Jim Vogt, P.E., responds: According to the
best available data, roof truss movement occurs in a very small
number (approximately 20%) of reported cases of partition
separation. This movement is typically caused by differences in
the moisture content between the top and bottom chords of the
truss. Other potential causes of partition separation
- Building settlement caused by undersized
footings, shallow footings subjected to freeze/thaw cycles,
and soil movement due to seasonally fluctuating moisture
- Inconsistent framing, such as uneven stud
lengths and irregular floor decks.
- Moisture-related effects. Framing members
will shrink and swell with changes in humidity. This is
particularly true for solid wood joists and studs
manufactured from juvenile wood.
- Beam and joist deflection. When beams or
floor joists aren’t stiff enough to support the
applied loads, the resulting excessive deflection can
contribute to partition separation.
Preventive action during construction is the best way to
avoid costly repair work. Properly balanced attic ventilation
helps prevent partition separation by exhausting moisture from
the air in the attic space. Continuous eaves and ridge
ventilation is most effective.
When appropriate, "floating corners" should also be used to
minimize the possibility of cracking at wall and ceiling
intersections (see illustration, above).
Before jumping to conclusions, it’s important to
investigate and determine the cause of partition separation
problems. Use a transit or laser level to determine whether the
floors, walls, or ceilings have moved.
Specific solutions should be handled on a case-by-case
basis. In the majority of the cases, retrofitting floating
corners with appropriate back-blocking solves the problem. Care
should be taken to remove the fasteners attaching the wallboard
ceiling to the trusses within 16 inches of the wall-ceiling
A second possible solution is to install cove molding at the
corner. Make sure to attach the molding through the ceiling to
the trusses but not to the partition. This allows the partition
to move independently of the molding; any gaps that occur
between the partition and ceiling will be covered by the
Jim Vogt, P.E., is a technical services representative at
the Wood Truss Council of America.