I-Beam Joist Flanges
Engineered wood I-beam joists were first introduced in the late 1960s and were used mainly in high-end home building. However, today up to half the homes built in the United States now use engineered wooden I-beams. They are considered an excellent alternative to sawn lumber for floor joists due to their strength and overall stability.
Wood I-beams consist of a center section constructed out of a layer of Oriented Strand Board (OSB) material that is sandwiched on top and bottom by two wide flange sections made out of finger jointed sawn lumber.
There are cut-out or knock-out holes in the OSB material that can be easily removed for running electrical wires and/or heating ducts. These knock-outs make it convienent for contractors to work with, eliminating excessive drilling/or cutting of holes.
Engineered Wood I-beams have several major advantages. First of all, they usually are much stronger, straighter and stiffer than conventional sawn lumber. Data indicates that they are 50% stiffer than sawn lumber. And what I like is that they shrink less. Consequently with less deflection and less shrinkage, this translates into better floor construction.
Of particular importance, while the house is under construction, is to Not cut or notch the top and bottom flanges. These flanges are what gives these joists their strength. When a contractor cuts or damages this component part of the I-beam, they may have critically damaged this structural component. To instigate a proper repair procedure, the manufacturer needs to be contacted. Since these are engineered wood components, only the manufacturer can tell you how to correct a defect.
As you see when you enlarge the photo, the plumbing contractor has notched below the bath tub drain which weaken the joist dramatically. Large holes can be made in the plywood web to a certain extent and the I-beam is not affected. But stay away from the flanges, as it is taboo to cut or alter them in any way.