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So I've taken out a section of wall between my kitchen/living room and am leaving only a knee wall (41" high) that will have a breakfast bar on top of it. Removal of the wall went fine, however, the remaining knee was is fairly flimsy and does not tolerate side load at all. Kitchen cabinets will go along this wall and probably add some stiffness, however, the fact I will put a breakfast bar on it makes me think I need more rigidity.

I would like to stiffen the wall and am thinking the most appropriate solution would be using a Simpson hold down, although I'm uncertain on both the hardware and blocking that is necessary. The wall itself does not sit directly above a floor joist but is instead offset so that the outside edge of the wall follows an inside edge of the joist (see picture below). I'm thinking that bolting the bracket through the baseplate to the subfloor won't do much, so it was my plan to run a 4x4 the length of the wall in the corner of the joist and subfloor, then run a threaded rod through it.

Simpson depiction My Setup

Questions:

  • Does this sound like a reasonable solution for bracing an existing knee wall?
  • Is that an appropriate hold down for this application?
  • What hardware would you recommend securing the 4x4 with to the joist/subfloor?
  • What diameter threaded road would you recommend for the anchoring?

Thanks

  • Also, I was considering this: homedepot.com/p/… tension tie as an alternative to the DDT2Z. It looks like it'd offer more support, however, I admittedly do not understand the difference between a hold-down and tension tie. – DrTarr Jun 4 at 16:24
  • Hold downs and tension ties are basically the same thing. Hold downs are usually installed with SDS screws and have much greater tension capacity, often needed for portal framing. This is compared to tension ties that are usually installed with nails and have less capacity, often used to prevent i-joists or floor trusses from pulling out and falling out of their hanger or off their supporting ribbon or ledger. – Dotes Jun 5 at 14:31
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Yes, you're on the right track to improve lateral stability. Your ideas will all help.

Some things to add is a layer of OSB or plywood as wall sheathing on one or both sides, if possible.

Another thing would be joist blocking in the floor below. An example of that would be a few 14.5" long 2x10 between the joists a bay or two on both sides of the knee wall (if your floor is 2x10 at 16" OC.)

Use screws and subfloor glue instead of nails for this. You already know it's not strong in the one direction, but also try to imagine how everything will move if you installed a countertop and a person lifted up and pushed down on the edge. The top and bottom plates will try to rotate, but the OSB/plywood wall sheathing will resist that. Screws and glue will also prevent that rotation.

If your wall would be too thick with OSB/plywood, then at least use Simpson coil strap along both sides of a few studs to prevent rotation between the studs and plate. What I'm saying is that even if you make the studs stiff, your next weak point is at the plates.

Even if your wall is super stuff, next the floor sheathing (and the single floor joist under it) will flex/bow as the wall is wiggled, so that's what the floor joist blocking is for. If you can't do full depth joist blocking, do cross bracing (it's like making an X with 1x4s.) The tops of your floor joists can't move since they're connected to the floor sheathing, but the bottoms of your joists are the place that movement will occur, so adding something to stop that will help, even if it's just a direct applied drywall ceiling/lid below.

Kitchen cabinet lowers will help so much more than you think. I've had to put countertops with and without cabinets on a knee wall for commercial receptionist desks and the difference is night and day. We always overkilled it if there wasn't a cabinet to hold anything, since we can't stop people from sitting on the edge of the countertop after it's installed. Cabinets added a ton of stability though.

  • Thanks for the info! I understand the 2x10 blocking will help prevent twisting of the floor joist, that seems easy enough to do. However, if I still use the hold downs for stud support I would still need the 4x4, correct? Or are you suggesting that I block and add another hold down on the block itself? So the bolt would go stud hold down->baseplate->subfloor->hanger(attached to floor joist)? – DrTarr Jun 4 at 16:09
  • @DrTarr Skipping the 4x4 and attaching an upside down DTTZ2 to the face of the added joist blocking would be ideal. You typically don't need to use joist hangers on the joist blocking, toenailing is usually fine, but in your situation it couldn't hurt to use some especially on any joist blocking that's connected to the knee wall with threaded rod. – Dotes Jun 4 at 18:00
  • Gotcha. I actually remembered that I have a supply air duct going between these two joists. Is there an alternative arrangement that could allow a 10"x3.25" duct to pass through? I think that's why I initially settled on the 4x4. – DrTarr Jun 4 at 19:35
  • @DrTarr I'd temporarily remove the duct and install joist blocking with 10.5" x 3.75" holes cut in it where the duct was, then reinstall the duct though the joist blocking after you've installed it. The blocking isn't structural per se, so cutting holes in it is fine. I'm assuming your joists are 2x10. – Dotes Jun 4 at 22:47

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