Trying to determine appropriate beam size for a header on a large sliding glass door
I’m not sure I completely understand the layout, but you can tell me where I’m wrong.
There is no floor load resting on this wall/beam.
The roof load has a span of 20’, so 10’ rests on the wall/ beam and the other 10’ rests on another wall. So, depending on where you’re located, normal snow loads range from 25 lbs. per square foot (psf) to 35 psf. I’ll use 35 psf.
Therefore, the roof load is 10’ x 35 psf = 350 per linear foot (plf).
Plus the roof load from the patio roof is 16’ / 2 x 35 psf = 280 plf.
The wall load on the new beam will be about 10’ high (2 storey minus the 9’ sliding door height). Most walls weigh about 10 psf to 15 psf. I’ll use 15 psf. Therefore, the wall load on the new beam is 10’ x 15 psf = 150 plf.
So the total load on the beam is
350 plf + 280 plf + 150 plf = 780 plf.
So, depending on the species and grade of lumber, a 6x14 beam can span 15’ and carry 780 plf.
I used SPF lumber with a “Select” grade. I noticed you were hoping to use 2- 2x12’s, so I presume you are working in a 2x4 wall. If you want to use 2x12’s, I’d use 5-2x12’s to span 15’ and support 780 plf.