Roof Truss Uplift In Winter

Since wood is a hygroscopic material any of the wood that makes up the truss that s exposed to the air in the attic releases moisture in the winter months.

Roof truss uplift in winter.

Roof truss uplift occurs when the bottom chord of the truss is exposed to significantly different moisture and or temperature conditions than the rest of the roof truss. The same truss could have different uplift reactions depending on which method is used. Truss uplift has nothing to do with plastic surgery or under garments. Truss uplift occurs in homes when the bottom of the trusses separate from interior partition walls during winter months.

Uplift reactions can occur with gravity loads on multiple bearing trusses. Cut through the nails holding the truss to the wallplate. Truss uplift occurs in homes when the bottom of the trusses separate from interior partition walls during winter months. The bottom chord that s buried in the insulation tends to have a higher moisture content because it thinks it s much warmer in the attic than it actually is.

It is a phenomenon common in homes built with roof trusses as opposed to rafters. When a newer house shows signs of interior cracking at the ceiling of the top floor in the winter this can normally be associated with truss uplift. Figure 3 roof truss in uplift position. The wider the span of the truss the more often the problem seems to present itself.

Truss uplift is a strange almost unexplainable occurrence that happens in new homes when the bottom of the trusses separate from non supporting walls during winter months. Figure 2 roof truss in normal position. For example if the bottom of the truss is buried in insulation while the remainder is in the open attic air this condition can occur. They drop back down in the summer.

There should be a small gap between the truss and the top wall plate. 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. This separation breaks the taped joints between ceiling and wall drywall as shown in figure 3.

The wider the span of the truss the more often the problem seems to present itself. Truss uplift is not structural problem it s a cosmetic problem caused by temperature differential. If you are lucky the gap will be large enough to easily slide a hacksaw blade between the pieces of wood. Figure 3 roof truss in uplift position.

Figure 2 roof truss in normal position. If a house suffers from truss uplift the top floor ceilings literally lift off the interior walls in the winter. Roof truss uplift occurs when the bottom chord of the truss is exposed to significantly different moisture or temperature conditions than the rest of the roof truss. As always if you have any questions concerning the engineered calculations on the truss design drawing you should contact the engineer sealing the design.

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.