month I would like to publish a few answers to questions
about I-Joist framing that I have received over the past
few weeks. I figured the answers might assist others as
What is the difference between a "squash block"
and a "web stiffener" in I-Joist (some call them
TJI) engineered truss floor framing?
Squash blocks are installed in I-joist framing where there
are point loads from above, such as posts under headers,
posts under roof or other loads, etc. Squash blocks are
usually 2x4 (many times multiple) blocks cut about 1/16-inch
longer than the depth of the I-Joist (for settlement/shrinkage).
Squash blocks extend the full height of the joist from flange
to flange. Web stiffeners are usually required over less
than 5" wide intermediate bearing points and some other
locations. Web stiffeners help reinforce the plywood or
oriented strand board webbing in the truss where it is stressed
at a bearing point to prevent deformation. Web stiffeners
should be attached with at least three clinched nails and
extend from the top of the bottom flange to about 1/8-inch
from the bottom of the top flange. The size of the material
for the web stiffener depends upon the style of joist. Typically
at least ½-inch by 3-inch material is required.
Web stiffeners are different than "backer" or
"filler" blocks. These backer blocks are typically
installed at hangers, and are larger to accommodate at least
ten clinched nails.
would recommend all inspectors obtain installation instructions
for I-joists, particularly if you are inspecting newer homes
and/or new construction.
good field reference is the Truss Joist Framer's Pocket
Guide to the Frameworks ® Building System by Weyerhaeuser
(check out www.trusjoist.com).
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