I'm working on calculating beam sizing to support one end of a mid-beam for a vaulted ceiling. The room is 16×20, with 4×10 beams spanning the 20' distance (48" O.C.). There is a mid-beam in place (4×14) spanning the 16' distance. That load is then transferred to the footing (concrete slab) through an existing wall on each end. I'm wanting to remove the wall on one end, and supporting this beam is the only structural aspect of this wall. I'm wanting to put a flush beam in place.
The live load to use is 20psf. I'm estimating the current roof system (clay tile & t&g) around 15psf. I have roughly then estimated the load on this flush beam to be approximately 2700lbs. However, this load is not spread evenly, and is approximately would be entirely in the center. I'm looking at using a parallam PSL beam, but haven't really decided how to select the proper beam for this application. Any suggestions or critique of my estimates would be helpful.
Best Answer
I suspect the loading on the new “flush beam” is more than the 2700 lbs. outlined in the question. I calculated 2800 lbs. and that’s without the weight of the upper wall resting on the new beam. (However, I think that would be about 250 lbs. per linear foot on the new beam.)
Depending on the species and grade, a new 4x10 beam 20’ long can support about 2800 lbs. mounted in the middle of the span AND a 4x12 beam 20’ long can support about 3100 lbs. mounted in the middle of the span. (I used a SPF species with a higher than normal grade... like “select structural”.
In addition to holding everything up, you’ll need to hold everything down too, if you live in a high wind area. I’d use Simpson steel connectors between the existing beam and new beam.
Remember, the support posts (and footing) at each end will need to support about 1400 lbs. minimum.
If you’re located in a seismically active area or high wind area, you’ll need to check for shear walls, etc. too.