Drilled a 45 degree angle between two sister joists - Am I okay

[rambo1970]

I stupidly bored a 45 degree angle 3/4 hole into two sister floored joist (each are 2x8 lumbered). Then I even more stupidly drilled a horizontal hole through them to inorder to run some electrical wire. I'm worried that I might have hurt the integrity of the joist. It starts at about 1.5 inches form one joist edge and then comes out near the center of the of sister joist. The combination of the two hoes in proximity to each other are no large then 2 inches. Should I be worried long term about this?.

The sister joist is about 10 feet long and run form a metal house frame to a bracket. There is also a door frame with 2x4 studs leading to a room in the center of the joist - so it has three support columns.

see attached image

[pushkins]

Holes by code are required to be 2" min. from the top or bottom edges of lumber and 2" away from any other hole and the hole diameter is not to be bigger than 1/3 of the depth of the lumber.
You are obviously closer to the edge than 2" but well within the hole diameter even if you add both holes together (due to proximity to each other) however I doubt you've caused any major problems.

You say they are sister joists , why were they sistered ? "sistered" usually means the original was faulty and another was added to it to increase strength. Or is this a double joist installed at construction time to carry a load from above ?

[rambo1970]

Hey thanks for the quick response. Yes they are just double joist installed at construction (not sister) Also, that's kind of what I thought, just add both holes together and treat it as if I made a 2" whole which is within a safe range for a lumbered 2x8.

Hypothetical for the engineering type out there... does drilling a bore hole at an angle make say a 2x8 joist weaker then drilling a bore straight through center (90 degree).

[HayZee518]

a 3/4" hole is normal in construction and wiring. if it is drilled at approx center or 2 inches from any edge it will be ok. I wouldn't, however, drill any holes in an engineered truss bottom edge. all the forces that the angles supply are transferred to the bottom stringer.

[pushkins]

Hypothetical for the engineering type out there... does drilling a bore hole at an angle make say a 2x8 joist weaker then drilling a bore straight through center (90 degree).

Technically yes it does make it weaker but it all depends on how steep an angle for how much weaker. At 90 degrees your cutting a cross section of material 3/4" in diameter straight through the lumber so the equation would read 3/4" (.75) x 3.14 x 1 1/2" (1.5) = 3.5325 sq. " of material, for any angle greater than 90 degrees you would obviously be removing more material but what makes it worse is that your cutting across so much more of the lumber grain fibers. Imagine drilling at 150 degrees that would be approx. 1" from the bottom of the 2x8 and exiting 1" from the top edge if you used a 3/4" bit the equation would read (approx) 3/4 x 3.14 x 6 = 14.13 sq. " for the same size hole BUT you have in fact almost drilled the 2x8 in half rendering it almost useless.

[HayZee518]

that discussion is a little absurd, isn't it? makes sense for the amount of material removed and hypothetically it is possible, but who's likely to bore a hole at 150 degrees?

[HayZee518]

I got to thinking about your formula for the amount of material removed. the 3.1416 is a constant and the 3/4" is the diameter. that figures out the circumference of the hole not the area. area is measured in square inches, foot etc. the area of a circle is PI R squared, so 3.1416 times the radius squared or .375 squared times the hole length.
.375X.375X3.1416=.4417875 X 1.5 inches = .66268125 square inches.

[pushkins]

that discussion is a little absurd, isn't it? makes sense for the amount of material removed and hypothetically it is possible, but who's likely to bore a hole at 150 degrees?

It kinda is, that's one reason I said "technically" however I often see holes drilled down through bottom plates for either electrical or plumbing that just happens to go through joists at steep angles, very often load walls sit directly over double joists and the only way to get utilities through them is to drill down. Many times you see a 3/4" or larger hole drilled down through the bottom plate and pass through a joist at a very steep angle. I have a job coming up soon that the plumber cut a huge notch out of the top of a joist to get the 3" pipe and flange up to a toilet and the joist right behind it has a 3/4" hole drilled right down the center to bring the water line up (I felt sorry for the plumber joists are on 12" centers so inevitably he was gonna hit both).
My reference to "150" degrees was for the point of math and the likes of the above examples of when it does happen, all due respect to plumbers and electricians, I am also aware area of a circle = Pi r 2 however my equation was for circumference area and the cutting of the grain fiber of the lumber. The inside of a hole is meaningless as it's the physical cutting of the grain.

[rambo1970]

well fortunately there is no wall above and if I did happen to weaken it; being that bottom hole on the second joist is within 2 inches, there is a third 2x8 just 2.25 inches away on one side of the double joist and a fourth one 9.75 inches away on the other side. Heck that's kinda why I was not able to make the correct hole in the first pass until I realized I'm an idiot and should have gotten a bit extender.

See I found a light switch in a near by closet in the basement with an old wire run to it just hanging on a gas line, hot and cold water pipes and a heat duct (not a return).