This is the answer that I gave the gentleman:
---------------------------------------------
Mr. Doe,
It depends greatly upon where the holes are located in relation to the span. As a rule of thumb with I-joists, you want to stay towards the center of the span for large holes. I have seen holes that would accommodate an 8” round duct through the middle of the span without any problem. If you can, try to stay within the center 1/3 of the span. If you are drilling “near the foundation wall”, you may have a problem. If I were inspecting the job, I would ask for the manufacturer of the product to provide approval.
In my neck of the woods, the suppliers of these products are very helpful to provide this information free of cost. I would consider contacting the supplier (not necessarily the manufacturer) and get their advice.
I’m sorry I don’t have a better answer for you, but the rules for I-joists are not set in stone. They are different depending upon the manufacturer and other variables, such as span, spacing and sizing.
Hope this helps you, Ryan Jackson
---------------------------------------------
Great answers guys! That is exactly the way I view it. I think there is a fine line between helping someone with a question and praticing unlicensed engineering...I'm not willing to cross that line and glad you guys aren't either.
