I'm in the middle of remodling the 2nd floor of our 1955 cape. We found a place where the PO attempted to drill through one of the doubled up floor joists around the stairs. But its not a hole drilled through the side, its drilled from the top down.
The first two small holes only go in about an inch, the third larger hole goes just about all the way through. Is this hole too large? If it is, is it sufficient to bolt another joist, perhaps 4' long, next to the damage? Only the first half of this joist is visible (the section in the knee walls, and a bit into the living space where an old wall was removed), the rest is still under the floor boards.
Best Answer
Determining if the drill hole weakens the beam beyond serviceability would require site-specific calculations, like how close to its load and span limit it is.
If it fails in the future, by cracking and sagging or collapsing, it will do so under heavy load, which is exactly when you don't want it to fail.
The floor will be on, and no-one will remember there is a slightly weak spot at that point.
For peace of mind, fit the bandage you've shown. It's a quick easy fix, and good for the long term performance of the building.
I'd be inclined to fit a much longer bandage, with two sets of through bolts far apart on each side of the fault hole, and perhaps use a 1/4" x 6" steel plate rather than wood.