Truss Uplift
When a house shows signs of interior ceiling corner cracking at the top of the wall, it is commonly due to truss uplift. Truss uplift usually occurs when the truss is exposed to a change in moisture and/or temperature conditions, causing the truss to arch up in the center. The ceiling drywall attached to the truss chords moves, causing cracks at the ceiling/wall junxture. Thiscreates a gap in the winter that closes in the summer.
Solution
When building a new house, the framing contractor should secure the interior partitions to the trusses with truss clips. The clips attach to the tops of the interior wall partitions and then are fastened through the slots to the trusses. In addition, proper drywall installation is necessary to prevent cracking. A common method of attaching the drywall together is to use the floating interior angle method with a backing angle.
However, many existing homes were built without consideration for truss movement. The preventive techniques listed below will allow the drywall to flex near the corners preventing cracking. The key is to connect the drywall on the ceiling and the wall together, while avoiding nailing or screwing them to the bottom of the trusses.
Prevention-REPAIRS:
1. The solution to an existing condition: The tops of the interior walls should be un-nailed from the trusses. Remove or cut free the nails from inside the attic. Then remove all the ceiling screws within 16 inches of the corners at the center partitions and all the wall screws within 8 inches of the ceiling along the wall. The holes in the drywall should then be patched, the corner paper taped, and the walls and ceilings repainted. This solution will be time consuming and costly.
2. Install crown molding around all the second-floor ceilings, attaching the trim only to the ceilings. This procedure would cover the cracks and maintain a nice ceiling corner. Note: When using this method, remember to paint the drywall underneath the area the trim will cover so there is no exposed unpainted stripe at the bottom of the trim when the trusses lift.
3. Change the way we insulate attics: Insulate against the roof plywood. This will create a conditioned attic, so the temperature and humidity will be better controlled. This will prevent differential movement of the truss chords.
4. Trim-Tex has a product called a “Truss Backing Angle” which is installed before the drywall is hung, helps prevent truss uplift. The vinyl backing angle keeps the inside corner stationary during truss uplift eliminating inside ceiling corner cracks.
The backing angle is made from vinyl, which is strong enough to hold the drywall edge in place along the top edge of the wall. It can easily be fastened anywhere along the edge, as long as the fasteners don’t go through the angle and into the truss. The screws start very easily in the vinyl, as compared to metal backing, which speeds up installation.
For more information and to request a sample of Truss Backing Angle, visit the product page here.
