Can I drill diagonally through the top of my beam?
I’ll try to answer anyway. I’ll make some assumptions and you tell me if I’m wrong.
The contributing load on the beam is 40 pounds per square foot (psf) Live Load plus 15 psf Dead Load for a total load of 55 psf.
If the joists on one side of the beam (and supported by the beam) spans 9’. So, half the 9’ floor load is transferred to the beam and the other half is transferred to the next support. Therefore, the floor load is :
55 psf x 9’ / 2 = 248 per linear foot along the beam, plus:
The weight of the wall above is about 15 psf x 4’ high = 60 plf
Therefore, the total weight on the beam is 248 plf + 60 plf = 308 plf
(I don’t think the stair connection contributes to the beam because it occurs at (or very near) a post. )
If the steel posts are 10’ - 12’ apart, there should be no problem drilling a diagonal hole within 3’ of the end of the beam. (Each 2x10 will support about 160 plf depending on the species and grade. 160 x 2 = 320 plf which is slight more than the required 308 plf.)
If the steel posts are 14’ apart, the allowable load goes down to about 120 plf, depending on the species and grade. (120 x 2 = 240 plf which is less than the required 308 plf.)
Holes not drilled in the middle third of the span are acceptable up to a certain size...and you are not approaching that size. (Btw, don’t drill multiple holes along the beam, especially in the middle third of the span.)
Note: make sure your refrigerator is not resting along this beam in any way.