Q&A / Truss Uplift and Ceiling Cracks Ceilings Remodeling text: Tim Carter. Truss Uplift and Ceiling Crack TIPS. Wood trusses move as the seasons change.

My living room shows 3-4 cracks in the ceiling that become bigger in the summer (up to 1/4') and nearly disappear in the winter. The cracks seem to run along joists. Usually, the cracks begin to grow as the temperature outside reaches 102 F (Mid-July here in TX), the cracks subside by the end of November. I think as the house/attic/roof expand in the summer due to hot temperatures, the ceiling drywall sheets separate and this action seems to be fully reversible and season/temperature dependent. I asked an engineer, his response was to add a couple of vents to the roof. I am not sure it will help. I would appreciate any advice as to how to stop these seasonal oscillations and cracks.

When a horizontal gap appears along the top of the wall, the likely culprit is truss uplift. Roof trusses, unlike roof rafters, attach only to specific walls plates. On other walls, the bottom chord of the truss lies on the plate but the roof builder does not attach it. Trusses are specifically engineered to move as a unit if the wood expands due to heat or humidity in an attic. This is an unwelcome, but not uncommon, problem with roof trusses. As the bottom chord expands, it bows upward, lifting the ceiling drywall with it and creating a gap between the wall and the ceiling.

Re-TapeThe least expensive method of repairing the crack involves re-taping the horizontal seam where the wall meets the ceiling. Before applying a new drywall corner bead and drywall joint compound to the crack, scrape torn bits of paper and dried compound off, and sand about 2 inches along the top of the wall and the edge of the ceiling. After filling the crack with new drywall compound and fitting a new corner bead in place, use an inside-corner taping trowel to create a crisp seam. After the compound dries, sand it and paint the wall and ceiling to match the existing colors.The problem with re-taping is that another crack can appear in the same spot if the truss isn’t done moving. Typically, a truss is more likely to move within the first year after construction. After that, truss movement gradually slows as the wood in the truss ages.

To avoid having to re-tape many times, monitor the depth of the crack over a year. When the size of the crack hasn’t increased for at least six months, go ahead and re-tape.

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Camouflage the CrackThe second least expensive method for fixing the problem is to camouflage the crack by installing crown molding along the top of the wall. The trick to doing this successfully is to choose a dark molding, such as an oak or walnut stain, and nail it only to the wall. After pushing the molding up to cover the crack, attach it with finish nails, inserting one into each wall stud, but do not nail the molding to the ceiling.

If the truss moves again and pulls the ceiling drywall upward, it’s less likely that the resulting crack will be noticed above the dark molding than it would be above light-colored molding. Float the TrussesThe only permanent way to fix the separation between the top of the wall and the ceiling involves loosening the drywall panels where they connect to the bottom of the truss and then attaching the panels to blocks installed between the trusses on the top wall plate. Called 'truss floating,' this project requires attic access, and it’s a job for an experienced framing contractor. The contractor will loosen the drywall paneling from the bottom truss chord and will push the edges of the paneling downward. He will install blocks on the top wall plate to hold the drywall down.

The seam must be re-taped.If the truss lifts again after that, it won’t pull the ceiling drywall up with it, so no crack will ensue. Many builders float the trusses during the initial installation of drywall.