I will be purchasing 28' I-Joists for a build. If the support LVL is dead center, so 14' span....would 9-1/2" I-Joists be substantial, or will they feel a bit spongy? This is assuming just 3/4" T&G OSB is used for the subfloor prior to carpet. The specs say they clear spans up to 16'6" with 16"o.c. but I have always used 11-7/8" thick I-Joists for my projects so I don't know how the floor would feel with the lesser I-Joists. Hoping to hear some advice from those who have or have worked with the two options to compare. Thanks.

Ok, now that I've got your attention... I have a house with a 10x20' side porch that was at some point closed in and finished. The finish work is decent and they tiled the floor. Checked with my laser level and the floor assembly is actually quite flat and level. Only problem is that the deck was originally framed with 2x6's running the long length of the porch. Under the room is a full basement and someone has gone in and supported the joists in a couple places, though not in the best fashion. My plan is to add a bathroom to one end of the 10x20 room - perhaps building a wall and making the bathroom 6x10. I'll keep the tiled floor in the entire space including the new bathroom, and add heating with pex from below. Before I do anything I want to properly support the joists. Even if I could get 2x8's or 2x10's into that room to sister up with the 2x6's the span is still too great. I'll need one or more beams to support the span. Perhaps I could put two beams in there, trisecting the deck so that the maximum 2x6 span is ~6.7ft. I'm also fairly sensitive to headroom. I was thinking I could cut the 2x6's and insert my new beams up against the subfloor, then use joist hangers to fasten the 2x6's to the beam, but I feel like I'd really be losing out on the strength of having continuous lumber. Ideas? [ATTACH]78055[/ATTACH][ATTACH]78056[/ATTACH][ATTACH]78057[/ATTACH][ATTACH]78058[/ATTACH]