MORRIS AND JAMES CAREY \ On the House Fixing tenacious ceiling cracks requires effort

A listener recently called our radio show to complain about an ongoing problem that she had been battling for many years.
Apparently, her home had been plagued by constant cracks at the joint where the walls and ceiling meet. She explained that over the years she had experienced minor cracks over windows and doors, but that repairs using fiberglass mesh tape and drywall joint compound had solved the problem. Unfortunately, when it came to the ceiling joint, she had little or no success with repeated repair attempts using this method.
When the cracks first began developing, her builder assured her that the cracks were normal and were the result of movement associated with building settlement, soil conditions and building material shrinkage. He explained that the cracks were temporary and that the condition would, with time, ultimately resolve itself. Needless to say, the builder is no longer in the area and the cracks at the ceiling to wall joint are as prevalent as ever.
Ascertaining the problem
We asked her several questions, which we hoped would help us solve the problem. First, where were the ceiling cracks occurring? Were they everywhere or limited to a confined area in the home? As it turned out, the cracks were appearing at certain interior partitions, but not at any exterior walls. We were also able to determine that the cracks were present at the ceiling at both sides of the walls in question and that, for the most part, all of the affected walls ran in the same direction.
Next, we wanted to know a bit about the roof construction of the home. Our primary interest was to determine how the roof was framed -- was it stick-framed or did it consist of manufactured wood trusses? As we suspected, it was the latter. Suddenly the picture became increasingly clear and we had a hunch that the callers home was suffering from a little known condition called "truss uplift."
Truss uplift
As the names implies, truss uplift affects homes that have roofs that are framed using manufactured wood trusses. In contrast to traditional stick-framing, where the rafters, hip, ridge and ceiling joist are cut and framed on site, a roof truss, which consists of the rafter and ceiling joist all-in-one, is manufactured in a plant according to specific design and engineering criteria. The completed trusses are shipped to the job on a large flatbed truck and lifted into place using a small crane. The trusses are installed according to the layout and toe-nailed to the double top plate of the walls.
Truss uplift results because of moisture content differences between the upper (rafter) and lower (ceiling joist) cords of wood trusses. Moisture content differences are typical when one is cold and the other is warm. Consequently, the bottom cord of a truss surrounded by a well insulated attic will be warmer than its cold rafter counterpart. The expansion of the top cord of a truss exerts an inward force on the bottom cord, which causes it to bow upward and lift away from the tops of interior partitions, hence the term "truss uplift."
The good news is that we identified the problem. The bad news is that there is no surefire means of preventing the condition from occurring. There is, however, a way of solving the crack at the ceiling to wall connection once and for all.
Fixing the uplift
Among the most effective fixes is to allow the bottom cord of the truss to float atop the interior partitions. This can be particularly challenging when you consider that the wallboard is securely fastened to the underside of the bottom cord of the truss with nails or screws. Therein lies the secret.
In order for the bottom cord of the truss to flex without causing a crack at the wall to ceiling joint, no ceiling drywall adhesive or ceiling drywall fasteners can be installed closer than 18 inches to the adjacent interior partition. Consequently, we recommended removing any fasteners located within this range.
We suggested that an easy way to determine fastener location would be to use a wood block and hammer in the attic to tap the ceiling wallboard away from the bottom cord of the truss. This would likely result in "nail pops" or exposed screw heads, which could then be removed.
The other part of the fix involves installing a slotted L-bracket anchor at non-bearing walls that would allow the truss to ride up and down in, but still provide a positive connection.
Once these fixes were implemented, the joint could likely be repaired once and for all. If for some reason the problem continues -- even on a limited basis -- we suggested installing a crown mold that is fastened only to the walls and not to the ceiling. Thus, movement could still occur and any seasonal cracks would be concealed by the decorative trim.
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