Roof truss movement or truss upliftDecember 16, 2009
Q. We live in a one level rancher and we would like to take care of a problem that occurs every year. Every winter the ceiling is separating from the wall and sets itself back into place in the summer. Is there something I can do to correct the problem before we install our new crown moulding?
A. The seasonal opening and closing of the joint between the ceiling and the wall
is caused by roof truss movement or truss uplift. This is caused by inadequate roof cavity ventilation and air leakage. During the heating season, warm moist air is carried into the ceiling cavity (Air Leakage) causing expansion of the bottom cord of the truss system. The expansion of the bottom cord causes the ceiling to go up. To correct this you must draft proof your ceiling cavity. For more information, contact Natural Resources Canada at 1-800-622-6232 and order their pamphlet dealing with Air Leakage Control. This pamphlet contains easy to follow instructions to correct your problem.
When you install your new mouldings nail them to the ceiling, not the wall, as is typically done so they are free to move up and down with the ceiling. If the mouldings are wide enough, it will cover the crack along the ceiling.
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