I-Joist

Also known as Fin Joist.

A manufactured structural building used as floor joists and rafters, so named as its cross-section resembles a capital I.

I-joists include two key parts: webs and flanges. The web, or centre, of the I-joist is often made of plywood or Sterling board. Large holes can be cut in the web to accommodate duct work and plumbing waste lines. The flange of the I joist may be made of laminated veneer lumber or dimensional lumber, usually formed into a 3.75 cm (1.5 inch) width.

The Euler-Bernoulli beam equation shows that this is a very efficient form for carrying bending and in the plane of the web, as well as shear.