I-joists are straight, so floors and ceilings lie flat. I-joists are stable because their moisture content is closely controlled. Shrinkage, nail pops and floor squeaks are a thing of the past. Promotional literature does make some exaggerated claims, however. Manufacturers promise big savings when installing plumbing, electrical and mechanical systems.
Thin webs are easier to drill through, and larger holes are permitted, especially in midspan.
But the word from the field is that few subcontractors see enough difference to offer discounts for I-joist jobs. Builders don't always save as much on labor as they're led to believe, either. Some of the more complicated framing schemes may even require crews to receive additional training. When working with I-joists, it's always good practice to provide detail sheets to the job foreman and to mark the locations for special fastening details right on the blueprints. Ironically, the design that makes I-joists such an efficient use of lumber makes them a concern for firefighters.