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We have a second story floor 12 ft long 2x12 16 on center. We want to put a 36 x 80 piece of equipment that's 400 lbs that vibrates. Looking for load specifically. Do we need to double 2x12 under the unit.

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  • 400 lbs isn't that heavy... 16" OC is pretty beefy... the issue isn't the load it is how bad the vibrations are and what they actually do. So for anyone to answer this they will need to know the specs on the machine that is vibrating. – DMoore Mar 25 at 20:40
  • @DMoore Vibration does not add to or take away from the strength of floor joists. Why do you think it does? – Lee Sam Mar 25 at 22:04
  • Have 3 friends stand close together and jump up and down that would simulate the machine I don’t think that’s very heavy for that large of an area. – Ed Beal Mar 25 at 22:10
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Each 2x12 spanning 12’ will support about 2250 lbs. depending on the species and grade of the joists.

So, total load is not an issue, but the strength of the subfloor and shear walls around this object could be a problem.

I’d check the subfloor and where the posts (if any) rests between the joists.

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  • Not sure why the down vote reversed. – Ed Beal Mar 25 at 22:11
  • @EdBeal I have a lot of answers downvoted. Not sure why, because I try to give code references or calculations with my answers. A couple of days ago I had 4 downvotes within 2 hours of posting my answer. That has to be a record on SE. – Lee Sam Mar 25 at 22:30
  • I have for years gotten down votes with no comment so I reverse most of them if there is no comment. But I agree that was a small load for that many square feet. Nope have had more when it was a simple 2 line straight code answer and a joke about my answer got more upvotes. My opinion is they come from people that really have not built anything but try to be internet carpenter and electricians. – Ed Beal Mar 25 at 22:32
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    @Rjsugar I’m not worried about holding this item up, I’m more worried about 1) the subfloor spanning from joist to joists is suitable, and 2) if the vibration (and shaking) could cause the room to rotate and shear the walls. – Lee Sam Mar 25 at 23:21
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    I've received a number of them too, with no comments... @Ed Beal has reversed many, I've learned from his example. – JACK Mar 26 at 12:17

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