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I Joists

Wood I-joists are very efficient at utilizing wood fiber. The flanges (the top and bottom of the assembled member) are designed to resist bending forces and provide stiffness to the product. The web section, typically plywood or oriented strand board (OSB) is designed to resist the shear forces in the joist. The connection between the two typically occurs in a groove in the flange where adhesive has been applied. The efficiencies obtained through the use of an “I ” cross section require additional considerations relative to solid rectangular sections. Design values are derived according to the principles of ASTM D5055, Standard Specification for Establishing and Monitoring Structural Capacities of Prefabricated Wood I-Joists.

Basement Ceiling Girder

Floor I-joists are supported at exterior walls and by girders. The I-joists can bear directly on top of the girder or be supported in joists hangers.

First Ceiling Framing

Ceiling cut-away reveals second floor framing bearing on exterior walls. The direction which the framing spans is not easily determined once the gypsum wallboard is installed and finished.

First Floor Framing

First floor framing is sheathed with wood structural panels and hardwood flooring. There may be no ceiling installed in a basement.

Floor showing foundation sill rim joist

I-joists and the rimboard commonly bear directly on a sill plate that is fastened to the foundation.

I Joist ceiling joists

I-joists generally don't have longer span capabilities than equivalent depth lumber joists. They are available in long lengths, which allows a single I-joist to span the entire width of a house, but with an intermediate support.

Joist cross section labeled

An I-joist is comprised of flange and web material. Manufacturers use different combinations of products, based upon many different factors.

adhesive

The web is joined to a groove in the flange with strict tolerance. Adhesive is used to secure the joint.

I Joist floor on steel I beam

I-joist floor assemblies can be constructed to bear on a steel girder and column system as shown in this single-family dwelling basement.

I-joist Floor with Blocking

I-joist floor framing just before the floor sheathing is placed.

I-joist floor

I-joist floor framing system under construction.

I-Joist manufacturing

This illustration shows the typical manufacturing process for I-joists.

I joist ply web solid flange

Early I-joists were constructed with solid sawn flanges and plywood webs. OSB has replaced plywood in the web, but lumber flanges are still common.

I-joist samples

I-joists are available in a variety of depths and web/flange configurations. Most I-joists used in residential construction are slightly deeper than equivalent solid lumber products.

I-joist TJI flange

The web material is matched to the flange to create a resource-efficient building product.

I-Joists in hangers to wood floor beam

Plywood floor sheathing is used in combination with I-joists and a LVL girder.

I-joists with ducting

Plywood floor sheathing is used in combination with I-joists. A section of the web has been removed to allow for the passage of ductwork and electrical wiring.

Second Floor Floor

Elements of a floor framing system.

Solid Sawn Girder

Beams and Joists Intersecting.

IBS bridging

IBS bridging is a manufactured wood bridging product that can be used with I-joists to increase stiffness and reduce bounce and vibration.