6

I'm putting a 56lb TV on a 20lb wall mount and attaching it to two studs with 5 screws (3 on one stud, 2 on the other). Installing the plate so it is off center would make the rest of the installation easier. My gut tells me this is a bad idea for like three different reasons.

Can anyone confirm or deny that intentionally shifting a lag bolt by an inch off stud center is a bad idea?

Thank you!

Update (and decision): The stud in question is at a 135 degree corner next to a bay window. Something I saw in an outlet hole plus holes I was drilling to check led me to believe I have a single 4" stud. I now believe that I actually have 2 or three studs next to each other.

Based on answers below, I want to hit the center of a dimensional 2x4, which is 0.75" from the edge. This actually buys me what I need. I originally thought I had to hit the middle of the 4", which is 2" from the edge. If all I need to do is hit 0.75" from the edge, that gives me an 1.25" extra inches.

| improve this question | | | | |
  • 3
    Screws and lag bolts develop strength based on size of the diameter, length, adequate thread cover (don’t over drill hole diameter), and adequate coverage around shank. All are self explanatory, except the last one. If you place the screw too close to the edge of a board, you will not develop full strength. In fact, the fastener could “pop out” of the lumber when stressed...especially if angled into the wood. – Lee Sam Nov 21 '19 at 7:27
  • See diy.stackexchange.com/q/178771/97780 – Solar Mike Nov 21 '19 at 9:00
  • Plate a little off centre is not a problem. screw off centre could lead to failure – Jasen Nov 21 '19 at 10:28
  • Simpson has #9 screws that are rated over 100 lb each. You still don't want them too close to the edge of your stud, but the smaller diameter than a lag bolt gives you a little more freedom. You have only 20 lb per screw. – Ross Millikan Nov 21 '19 at 15:31
  • @RossMillikan Simpson's offerings are pretty slim compared to others (SPAX, GRA, Paulin, Fastenmaster) - there are a wide array of structural screws which are rated to replace lags. – J... Nov 21 '19 at 16:01
7

Not clear as to where your location is but here in the USA the studs are 1.5" thick. The centerline to edge distance of the stud is 0.75".

If you try to move the lag bolt over by 1.0" from the center there will be no stud for the lag bolt to go into. That is unless you get very lucky and happen to be working in an area where there is a doubled up stud.

Bottom line with only 0.75" to deal with in either direction you should aim to keep your bolts centered on the stud ... or at least try not to deviate off center by more than 0.25".

| improve this answer | | | | |
  • The other option here is to open the wall and add blocking but I'm going to guess it's easier to deal with an off-center plate. – JimmyJames Nov 21 '19 at 15:03
  • Yeah, these are 1" thick wood panel walls. I don't want to get into trying to patch and repair them. – LoftyGoals Nov 21 '19 at 16:02
  • 2
    @LoftyGoals 1" thick wood walls.... there might not be a ton of need to hit a stud in that case. Is the wall itself strong enough to hold the TV? How are you able to reliably find studs on a 1" thick wall? – Brad Nov 21 '19 at 18:36
  • @Brad Excellent question, which is why I had to ask it here (diy.stackexchange.com/questions/178717/…). – LoftyGoals Nov 21 '19 at 22:15
  • @Brad I was also wondering if the paneling would be enough to support 76lbs by itself. More smaller screws would probably be in order. – JimmyJames Nov 21 '19 at 22:17
8

Yes, keeping lags centered in studs is important.

The following is minimum for BOLTS IN WOOD:

Edge distance:

  • Perpendicular to grain: 4 times dia.
  • Parallel to grain: 1.5 times bolt dia.

End distance:

  • When in tension: 7 times bolt dia.
  • When in compression: 4 times dia.

Center-to-Center spacing:

  • Perpendicular to grain: 2.5 times dia.
  • Parallel to grain: 4 times bolt dia.

Spacing between rows of bolts:

  • Between 2 and 5 bolt diameter depending on l/d ratio
| improve this answer | | | | |
  • So a 1/2" diameter lag screw into the 1.5" side of a 2x4 can never happen? as it would be parallel to the grain at 1.5 x .5 = .75 from either edge which leaves zero to account for the actual diameter. You'd need at minimum a 1.5+.5 = 2" effective width as the bare minimum? – Fresh Codemonger Nov 21 '19 at 8:12
  • 1
    @FreshCodemonger Yes, these are the minimum clearances to develop FULL resistance as established by the Western Woods Product Association in structural design. However, most design does not require 100% full resistance...but it does illustrate the need to be careful and install fasteners as close to the center of studs as possible. – Lee Sam Nov 21 '19 at 9:04
  • 1
    @FreshCodemonger In other words, if your TV actually needed the full strength of a 1/2" lag (which should hold several tons or more), you wouldn't get it stuck into the 1.5" face of a stud. The bolt and stud will fail before you reach the rated "book" strength of a 1/2" lag. The TV most certainly does not need the full rated strength of five 1/2" lag screws, however, so even though the installation is sub-optimal, it still produces a sound enough attachment for the application. – J... Nov 21 '19 at 13:29
2

I'd keep the wall mount plate centered and drill new holes in the mount plate to match the center of the stud.

| improve this answer | | | | |
  • Unfortunately the holes in the plate are already at the edge of the plate. – LoftyGoals Nov 21 '19 at 16:02

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.