My home is a 2 story home, built in 2003. There is one section in the home that was left open to above with approximately a 20' ceiling in this case. This is over the living/dining areas of the home and it is a substantial amount of space. I would like to fill in that space to expand the second story.

Now, I know that I need to get my plans approved not only by a structural engineer but also the city and I will do that. However, I am drawing the plans myself so I just want to make sure what I have is reasonable first.

The home has existing engineered wood products, for example the second story existing area is supported by wood I-beams that are 11-7/8" deep. So, I am trying to match that. Here is what I have and I just want to know if this is reasonable. I used software provided by Weyerhauser (although Roseburgh, LP and the like all have similar software) to put in all my specs and it says "Passed" but I just can't wrap my head around the fact that all of the I-Beam joists can hang from one engineered beam and support all of them, along with the second story I am adding.

Note, when I did the calcs, I over specified the loads (live, dead and deflection) above and beyond what code calls for.

Here is before and after floorplan Before and After Floorplan

Here are all the calcs for the beams. Beam Calcs

  • I didn't churn through the charts and everything, but I can speculate that it'll work out as you expect. The beam only really holds the new floor system, any interior walls that you add, and your lifestyle stuff (furniture, whatever). It doesn't carry the roof at all. However, the beam will likely be taller than you have drawn--somewhere around 16-10". If you need to keep it that short, you may need to go with steel. – isherwood Feb 2 '17 at 21:31

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