Why Truss Uplift?
The way in which houses are built has changed over the years. Attics of newer houses have more insulation and ventilation. They also have roof trusses instead of rafters and ceiling joists. The bottom chord of a truss is buried below a deep blanket of insulation. Even on the coldest days the bottom chord is insulated and warm. In such cases, it is also contracting. The top chords are doing just the opposite because they are above the insulation, they absorb moisture from the air, which causes them to elongate. With the top chords growing and the bottom chord shrinking, the truss arches upward in the middle, causing the ceilings to lift off the walls. In the summer, this cycle reverses itself.
