AN UPLIFTING EXPERIENCE - Explaining Truss Uplift
By Tim Oglesby, Home Check
America
Truss uplift is a common
phenomenon in homes built with roof truss systems. A truss is a
prefabricated roof structure, which holds up the roof decking wood,
shingles, and top floor ceiling. They are assembled, usually from
2x4 lumber, in a building material factory. The 2x4’s are held
together with either metal or plywood “gusset plates”.
Trusses tend to be stronger, lighter, and less expensive than
rafters. Trusses are strong because they make use of the most
efficient geometric shape, the triangle. The outside members of a
truss are called chords while the inner pieces are known as webs.
Each component is important because they apply pressure onto the
other two sides of the triangle, establishing support balance
between each other. They are less expensive than rafters because the
lumber thickness and lengths are smaller.
WHAT IS TRUSS UPLIFT?
If a house experiences truss
uplift, the top floor ceiling literally lifts off the interior
walls, usually in the winter, then drops again in the summer. It may
appear that the floors or walls have settled, but actually the
ceiling has moved up, then down. Sometimes the gap can be as much as
an inch where interior walls meet the ceiling.
Modern construction places the bottom chord of the truss below a
deep blanket of insulation. Even on the coldest days the bottom
chord is nice and warm. The top chords however, are above the
insulation and get very cold in the well ventilated attic. The
bottom chords are warm and dry. As the warm air from the home
travels through the top chords they begin to condensate with the
cold air of the winter season. It’s kind of like the condensation
that occurs on the outside of a ice cold glass of water on a hot
summer day, only in reverse. As the top chords begin to absorb some
moisture from the air, it causes them to elongate, or swell.
With the top chords growing and the bottom chords shrinking, the
truss arches up in the middle to account for the pressure
differences, thus lifting the truss off the interior walls.
IS THIS A PROBLEM?
From a structural standpoint, it
is not a major problem. But cosmetically, it may cause cracks and
separations in the drywall. A common question clients ask us during
the inspection is, “What about those small cracks along the ceiling,
aren’t those a problem?” Many homeowners “repair” the cracks with
drywall compound, only to have them reappear next year.
Some contractors have helped disguise truss uplift by securing the
ceiling drywall to the top of the interior walls and not the trusses
for 18 inches away from the interior walls. The drywall flexes and
stays fastened to the walls while the trusses lift above it. Others
use a decorative molding where the walls meet the ceilings. They
fasten the moldings to the ceiling but not to the walls. As the
ceilings move up, the molding go with the ceiling and cover any gap
that may develop. If this molding plan is used in your home, try to
decorate with this in mind.
About the Author
In 1984 Tim Oglesby unknowingly
bought a home with significant defects. In 1994 he began Home Check
America to assist new homeowners in NE Illinois. With a degree in
business and masters in management, Tim was trained as a home
inspector with Carson & Dunlop Engineering, was a general contractor
for eight years, and is a licensed home inspector and real estate
broker. He is a sought after public speaker and author on issues
important to property management and home inspections.
Contact:
www.homecheckamerica.com or call toll free
1-866-245-4663. Home Check America is responsible
for the content of its articles and has no
affiliation with the RE/MAX organization.
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