2

I'm looking to minimize how much my wall-mounted TV protrudes out of the wall by recessing the wall plate of the mount. The latter is going to be secured by 4 wood screws into 2x4 studs sitting 16" apart - in a square pattern across 2 studs. I'd like to "shave" the studs but don't know how much stud depth is required - in other words how long a wood screw I should use. Will 1.5" long screw be sufficient, for example? And so the stud should be slightly deeper - say 1.75"?

The TV + mount ~ 110LBS; the mount specs can be found here

2

There are many factors: 1) species of wood, 2) moisture content of wood, 3) diameter of screw shank, 4) length of screw, 5) wood screw or lag screw (lag bolt), 6) Direction of loading.

1) Species: Where I live, we use Douglas Fir-Larch framing lumber. It's considered "dense". Other softer species have lower strength values...some as much as 40% less.

2) Moisture Content: Green lumber (unseasoned) will not tend to split as much as "dry" or "surface dry" lumber. Assuming your wall has been built and has been in a dry environment for more than a year, it should not split, even when you "shave it" (as you call it). Also, I'm going to assume the fasteners will be more than 7 times their diameter so they won't split the wood.

3) Diameter: Because the fastener needs to fit within the stud WIDTH, the diameter is limited to the minimum edge distance of 4 times the diameter...and that assumes you'll be equal distance from each edge of the stud.

4) Depth: Assuming a minimum of about 1 1/2" into wood, the screw needs to be about 2 1/2" long to account for the 1/2" drywall plus thickness of the metal hanger.

5) Screw or Bolt: You said screw so I'll use screw.

6) Loading: Fastening into stud will be side grain (not end grain, which is about 75% less). Also, because the TV is hanging on the wall, loading is a combination of shear and withdrawal.

Therefore, I'd use a #8 wood screw (0.164" diameter) x 2 1/2" long (to develop full resistance) which will give you about 95 lbs. withdrawal resistance in close or medium grain "dry" lumber per screw.

Remember, you can only "shave" a maximum of 1 1/2" off depth of stud (don't over cut or it will weaken stud) and don't over pre-drill diameter of hole. To develop full lateral strength, there needs to be lead holes drilled (pre-drilled). Lead holes should be about 7/8th the shank diameter. Therefore, I'd use a 0.1435" diameter bit. (1/8") If the screw doesn't go in easily, you can ease the installation by greasing it up by rubbing the screw in a bar of soap.

  • This is great stuff. Can you by any chance share a general resource people can go to for other problems of this nature? – fixer1234 Jun 5 '17 at 1:03
  • 1
    @fixer1234 Yes, the information is from "Western Woods Use Book" with "Structural Data and Design Tables". It is published by the Western Woods Products Association in collaboration with the Western Pine Association and the West Coast Lumberman's Association. (It is published now in a more general format, so you'll need to know the specie's Fb extreme fiber in bending, Fv horizontal shear, Fc fiber shear strength perpendicular to grain and parallel to grain and E the modulus of elasticity. (I don't know if it's available on line, but I'd start w/ American Institute of Timber Construction in – Lee Sam Jun 5 '17 at 2:49
  • Englewood, CA; American Wood Preservers Association in McLean, Virginia; National Forest Products Association in Washington DC; or Southern Forest Products Association in New Orleans. ) – Lee Sam Jun 5 '17 at 2:54
0

Similar question here; TL;DR it depends more on the studs you're fastening to. The screw package may have specs on it. I would use longer screws assuming the mount and drywall will use up a bit of it.

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.