Modern technology has improved the materials available to the construction industry. Engineered wood products have pushed the design boundaries to lengths that seemed unachievable a few short years ago. Engineered floor joists are one of these new wonder products that give the architect and the builder more flexibility in design and the home owner a better, sturdier built house.
The longest engineered floor joist that you can order today are over 50 feet in length. Can you imagine the size of tree that would be required to produce a piece of lumber that is 50 feet in length and 24 inches wide? Think of the trees that are saved every year by making these monster joists from engineered wood.
To the observer unfamiliar with the physics involved with wood I-beam technology, it would appear that engineered joists are not strong enough to support the weight that they can support. I-beams obtain their strength because of the depth of the beam, not the width. To demonstrate this fact, just take a standard 2×4 of 8 to 10 feet in length, place it vertically, so that the narrow side is up, support it at both ends and stand on it. Next turn the 2×4 horizontally, so that the wide side is up and stand on it. Notice how much more the 2×4 deflects when the wide side is up. The strength of any beam is directly proportional to its depth and only minimally related to its width. So a thin, deep I-beam can handle the same load as thicker, shallower wood floor joists. The tops and bottom flanges of wood I-beams are important for nailing surfaces and to keep the thinner portion of the I-beam from twisting.