I-Joist Installation Tips

I-Joists are engineered wood products that are gaining popularity with building professionals. Engineered I-Joists are manufactured under exacting conditions to ensure consistent strength that provides long span and high load capabilities. These installation tips are supplementary to your manufacturer’s instructions and technical guides.

Load handling: Each I-Joist must be braced and nailed using appropriate joist hangers, blocking panels and Rimboard or bridging at the joist ends. Use a minimum of 1×4 temporary bracing during installation to prevent I-Joists from buckling. Do not place any loads on I-Joists until properly braced and sheathed.

Rim framing: This is the suggested installation method as it encloses the floor perimeter and transfers bearing wall loads to the wall below rather than the I-Joist ends.

Blocking is utilized for load transfer. There are two kinds of blocking that can be used:

  1. Blocking between joists which is utilized at interior supports near a load-bearing wall and where floor joists do not span over supports.
  2. Loads are transferred around I-Joists with squash blocks. Squash blocks help to divert loads from posts and columns.

Span capabilities and nailing patterns: These vary by manufacturer, so consult your design professional or manufacturer’s span chart to determine span capabilities and nailing patterns.

Storage and handling: Always stack I-Joists upright and level. Protect I-Joists from the weather and keep off the ground. Follow the APA guidelines for on-site lumber storage. Avoid stacking construction materials over unsheathed joists. Do not lift I-Joists by the top flange. Leave bundles wrapped until ready for installation.

Modification of I-Joists: While I-Joists can be cut to required length, do not cut, notch or drill flanges. Modification is discouraged as I-Joists are engineered to transfer floor loads to the joist supports and carry very high loads. When they are modified, their efficacy cannot be guaranteed. If an I-Joist has been damaged, do not attempt to repair it.

Web stiffeners: These wood blocks are utilized to reinforce I-Joists where there is a danger of buckling or where the webs are in jeopardy of slicing through the flanges due to excess loads. They can be made from rim board, OSB board or lumber. They are also used where I-Joists are supported in hangers that do not stretch to the top of the flange. With the top of the I-Joists unsupported, it can move laterally which would twist the top flange.

Web stiffeners can be designed for bearing or load. Bearing stiffeners are used at both interior and exterior while load stiffeners are located between I-Joists where point loads greater than 1,500 lbs. are applied to the top of the flange.

Web stiffener depth should equal the distances between I-Joist flanges less ¼ inch.

For bearing stiffeners, this gap will be positioned between the stiffener and the bottom of the top flange. For load stiffeners, this gap is positioned at the bottom of the stiffener.


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