My goal is to meet the code requirement for the strength of the floors on a 2nd story for a remodel.
I am remodeling a house where the floor joists supporting the 2nd floor are nominal 4x4 (3.5" x 3.5"). My problem is that by adding lumber of the correct depth (presumably 2x8) the ceiling height will be too low for taste, and potentially for code. The current ceiling height measured to the joist is 7' 10". My goal is to keep the current ceiling height by using aluminum or other metal as low depth joists to strengthen the floor (fitting into the current 3.5" depth).
I'm not an engineer, but I think my problem is that I'm exceeding L/360 deflection limit. Here's the scenario:
The 2nd floor area is a 23' x 20' rectangle (rounding up to the nearest foot). The floor joists run along the 23' length toward the center of the home, and they sit on top of a wall and beam combo with a 3.5" bearing. The joists run to 10' 6" on one side then sit on the wall/beam, and they run 12' 5" on the other side before they lap over the wall/beam. The 4x4 joists are placed at 13" on center. Very odd. Apparently, the 2nd story addition happened in the 70's and survived the 89 earthquake in Oakland CA.
What are your suggestions for keeping the current floor depth, but strengthening the floors so as to reduce deflection specifically, but more generally to meet code requirements for floor strength?
I was thinking of inserting some 3.5" x3.5" aluminum joists alongside the 4x4 lumber to increase strength and reduce deflection.