0

When it comes to vertical drilling into a joist, the internet is split in two:

One is discussions about drilling a large hole through the joist to pass plumbing/electrical/etc, and the answer is "don't do it!". There's discussions about the bending face, thirds of the joist, code, etc., and how any notching/drilling on the bottom of a joist - especially in the center 3rd - is the worst thing you can do.

The other half is about mounting stuff to the ceiling - on which there are... crickets. If you keep looking, you'll find mounting instructions for stuff (like lamps, fans, bike hangers or these 400lb and 600lbs racks), where screwing (vertically) into the joist is what you should be doing (as opposed to mounting to drywall), and as long as you're centered enough on the joist, there's nothing else to worry about. Pilot holes are welcome.

Can anyone help settle the discrepancy?

Personally, I'm mounting a 6lbs projector (+2 lbs mount) in the middle of a long timber ceiling joist in the middle of a living room; the ceiling supports a residential floor (another living room) above it. Barring new information, I've decided to use 2 x wood screws (#10 or #12 w/ 1/8" pilot hole) instead of thicker lag bolts, since those should easily support the light, static load while minimizing displacement of the joist material.

  • do this experiment ..... get a piece of 2x4 ..... screw a wood screw type hook or an eyelet into it .... attach a rope to the hook (eyelet) .... see how much weight you can lift with the rope before the hook pulls out of the wood – jsotola Dec 17 '18 at 6:21
  • The first paragraph refers to vertical drilling and the second paragraph refers to horizontal drilling. Please clarify. Also, the third paragraph refers to “crickets”. To me, crickets are something installed on roofs to help channel water to drains. How are crickets related to vertical or horizontal drilling into joists? – Lee Sam Dec 17 '18 at 7:36
  • @LeeSam I'll assume that's tongue in cheek, but just in case it isn't "crickets" is the sound a performer hears when he gets no response from the audience. Likewise, it's the response given by the internet when it has no response to give. – FreeMan Dec 17 '18 at 19:46
  • @FreeMan Oh, I see. I thought it was referring to a construction term, because this is a home improvement site. – Lee Sam Dec 18 '18 at 2:21
  • Just colorful writing. Wasn't aware 'crickets' was a construction term. :) "Crickets" = "nothing". Also, how is 2nd paragraph about horizontal drilling (in existing construction)? – Drew Dec 26 '18 at 21:59
3

I see your concern but there's really no discrepancy. The tiny pilot holes you will drill for your #10 screws to mount your projector do not remove any significant amount of material from the joist. They also don't go all the way through, just an inch or so. They won't significantly change the strength of the joist.

If you were drilling a 3/4" hole vertically all the way through the joist and running all thread through it, you'd be removing half the material in that spot, and that of course would weaken the joist significantly.

So where do you draw the line? I am afraid I can't give you an exact answer based on engineering calculations and testing. However I can give you a rule of thumb that has worked for me. I find that 3/16" x 3" pilot holes for 1/4" x 3" screws are adequate for anything you can hang off 2x framing, so there's no reason to go any bigger. That hole is smaller than the shaft of the screw but adequate to prevent splitting in framing lumber, and small enough that it doesn't significantly weaken anything.

I have mounted all kinds of equipment, often hundreds of pounds, using this rule of thumb without any problems. In the rare instances where I don't trust 1/4" hardware, rather than use larger fasteners, I'll use more fasteners; for example, sometimes I'll attach unistrut to framing with multiple 1/4" screws then hang the heavy stuff off the unistrut. This also distributes the load better.

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.