Hi, I have a masonry garage with a 18ft high ceiling and would like to add another level inside (a second floor, in other words).  I’d like to use Trimjoists to do this and was wondering if I could get a sanity check on the depth I will need.

The width of the garage is 19’3″ from brick to brick.  I want to clear-span this.  Looking at the span tables from trimjoist ( http://www.trimjoist.com/spans.html), it looks like I could use j-12’s spaced 24″ on center to get a L/465 floor with a load of 40-10-10.

Frankly, this sounds ridiculous to me.  I made the mistake of spanning 20 feet before on another project with 12″ trimjoists and spaced them 19.2″ OC and have one hell of a bouncy floor.

So I was thinking of just bumping up to the J-14 and spacing at 19.2″.  According to their table, even with a 40-20-10 load and L/539 defelction, I should be able to span over 24′ with this setup, and I only have to go a bit over 19′.

Does this sound like a good plan?  Will it too be bouncy or is it overkill?  Truthfully, I can’t tell because those span tables look silly to me.  Is there something I’m missing?

Also, most of the joists will go all the way across the 19′ , but will be shorter where my stair well is.  Should I still get the same depth of joist for that section for the uniformity of ceiling height in the space below, or should I save a bit of money and get smaller depth joists over that section?

Thanks in advance,

Cliff