I-joist

An engineered wood joist, more commonly known as an I-joist, is a product designed to eliminate problems that occur with conventional wood joists. Invented in 1969, the I-joist is an engineered wood product that has great strength in relation to its size and weight. The biggest notable difference from dimensional lumber is that the I-joist carries heavy loads with less lumber than a dimensional solid wood joist. As of 2005, approximately 50% of all wood light framed floors used I-joists. I-joists were designed to help eliminate typical problems that come with using solid lumber as joists.

The advantage of I-joists is they are less likely to bow, crown, twist, cup, check or split as would a dimensional piece of lumber. I joists' dimensional soundness and little or no shrinkage help eliminate squeaky floors. The disadvantage is very rapid structural failure when directly exposed to fire, reducing the time available for residents to escape and increasing the danger to firefighters.