Building a knee wall

[Lee Schierer]

I need to build a knee wall for a project. The knee wall will be attached to one wall and come out into the room about 5 feet. The bottom plate will be attached to the sub floor. How do you make the end that is not attached to the wall as stiff as possible?

[Tom Ewell]

One way to do it.
newel lag bolt (http://www.ljsmith.net/products.aspx?category=&type=9&product=17)

[Charles Wiggins]

Found on another forum:


The secret for me when framing something like that is really square cuts, screws and glue. I don't treat is as framing so much as serious joinery. I'd cut all the pieces on the miter saw, glue all joints (I like yeller wood glue instead of "construction adhesive" for this sort of thing if you've got a good fit) and screw them together with deck screws. I would strongly recommend the plywood on at lest one side if you have room for such. It'll make a world of difference in stiffness if it's well glued on there. I'm nearly always on concrete slab, but if you have access to the joists below a wood subfloor, cantilevering that wall on the side of the joist structure would also make a tremendous difference.

I've got nothing at all against using the steel angle braces, I just never have a good place to hide the floor end. If you do, it doesn't hurt to make use of everything that will help. Isn't there gonna be a tub or cabinet or anything on the off side of that wall that would allow you to hide a little extra bracing? Four by five foot free-standing wall's still likely to wiggle enough to crack the tile if a non-Atkins person slips and catches hisownself on it, doncha know. http://www.johnbridge.com/vbulletin/images/smilies/smile.gif

If it would work in your plan, framing that little wall with 2x6 would also help to stiffen it up if you've made good joints.

I will PM the URL.

[Kent A Bathurst]

Lee - I might be confused here, but....

The vertical part is framed like a wall - sill plate [anchored as you note], top plate, and studs.

Then - you anchor a ledger to the real wall with lag screws.

And - the quick way - use 2 x 4 sleepers and joist hangers on the ledger and top plate/studs.

Or - substitute lap joints at either/both end[s] of the sleepers.

[scott vroom]

4x4 post and newel bracket at the floating end, or if you have access from below a 4x4 post extended through the subfloor and mechanically fastened to a joist or joist blocking.

[Lee Schierer]

Lee - I might be confused here, but....

The vertical part is framed like a wall - sill plate [anchored as you note], top plate, and studs.

Then - you anchor a ledger to the real wall with lag screws.

And - the quick way - use 2 x 4 sleepers and joist hangers on the ledger and top plate/studs.

Or - substitute lap joints at either/both end[s] of the sleepers.

The basic framing I get, but making it so the top of the exposed end doesn't move it what I am concerned about.

I'm not sure what structure we will have under the floor, nor how much access we will have to it so longs posts or newel type lag bolts my not help.

Right now I'm leaning toward making it a glued and screwed torsion box assembly with a 1/4" skin and with the top plates extended into the wall and tied to a couple of studs.

[Phil Thien]

Short of going through the floor and attaching to structure, I can't imagine anything that won't wobble higher up.

[Peter Quinn]

Short of going through the floor and attaching to structure, I can't imagine anything that won't wobble higher up.

Me either. There is no short cut. Its hard to call without knowing the field conditions, but I'd consider cutting out a piece of ceiling from below and patching to make a solid connection if this wall is high enough to represent a tripping hazard. If it really needs to hold a persons weight and force in motion, then it really needs to go through the floor and hit structure. Or you need to change your phone number after install.

[Max Neu]

If it's just a wall with nothing else to add stability (like a base cabinet),you could have someone make a steel bracket that is T shaped.It would extend out on the floor in both directions,and run up the side (the 3 1/2" portion) of the wall and screwed to the floor and wall,which would tie the 2 together all the way up to the top of the wall.This is assuming you aren't working on the finished floor.This would probably be an easy bracket to make if you have a welder and a little metal working skill (which I do not).That's the kind of stuff you can have someone you know make for you that might only cost you materials and a 12 pack. :)

[scott vroom]

I'm not sure what structure we will have under the floor, nor how much access we will have to it so longs posts or newel type lag bolts my not help.

If you don't have access from below then I'd cut out a large enough section of subfloor to allow anchoring a post to the floor structure. Your original question was "(how do I) make the end that is not attached to the wall as stiff as possible". This is the way to do it. Doubling the top plate and tying into the stud wall will yield an inferior result.

[Tom M King]

Do the joists underneath run perpendicular to it?

[Yonak Hawkins]

As has been mentioned, attaching as deep and as well into the floor and the adjoining wall as possible is important. I also would make the knee wall as thick as possible, using 2 X 8s or 2 X 10s, if possible, and plenty of glue and screws. We have a 4' X 4' wall that's very firm but support is aided by the fact that it's at a corner and is part of the other wall.

[Sam Murdoch]

As has been mentioned, attaching as deep and as well into the floor and the adjoining wall as possible is important. I also would make the knee wall as thick as possible, using 2 X 8s or 2 X 10s, if possible, and plenty of glue and screws. We have a 4' X 4' wall that's very firm but support is aided by the fact that it's at a corner and is part of the other wall.


All this above and then -
Glued and screwed plywood faces (3/8" or better 1/2" or better 3/4") or some substantial (let into the studs) diagonal bracing if you can't go below the sub floor with the framing or at the very least - your terminating end framing. The diagonal support is all you can depend on without going below the floor. The point were the 1/2 wall joins the wall should be as secure and rigid as possible and then the ply or diagonal bracing ties back to the structure at the wall. What you described Lee in your post # 5 but with more skin. No question that a through the floor system is best (or to the ceiling) but if you can't then all you have left is bracing structure to make the piece move as a unit. Also, screw and glue the plate to the sub floor and your end stud gets fastened (yup, with glue and screws) to the end of the plate and toe nailed (screwed) into the floor. If the location of the sub framing (joists) work for you attach as much as possible to those. Even a small return at the terminating end (5" or 6") will help stabilize the wall.

[Lonnie Gallaher]

I work in the structural industry. There is only one way and that is to connect below the floor level. There cannot be any wiggle in the support above the floor level or the wall will not be properly supported. Steel is the material of choice in new commercial construction. Either a heavy angle, channel or a tube steel shape. One at the end of the wall and if the wall is more than about 8 feet there needs to be a second wall support at or near the mid length. The wall supports need to be lagged or thru bolted to the framing. Make sure the bolts are tightened again before the wall covering goes on.

[Max Neu]

I don't see how any amount of glue and screws will address the stability of the corner of the wall without actually getting support all the way up with either a metal bracket or a post from the floor up to the top.Without an actual post or bracket to support,it will end up flapping in the breeze in a short period of time with people leaning on it.

[Brian W Smith]

Didn't read the responses so excuse any repeats.

There's a few different approaches......experience is usually the guide here.In historic work the metal "can" be a deal breaker(further reading on this would be the UVA "catwalk" collapse)......not a rail section,worse.

But sidestepping the above......metal pipe of sufficient diameter can be BURIED into the framing."Grout" probably is the correct term,we use a high quality automotive "Bondo"(rage gold) as an expedient.

Back to historic for the next one because of it's time honored sucesses.It's a wedge that acts on a buried wooden post.The bttm of which is spilt.......the wedge is placed in the bttm,then when the post is driven down with a sledge hammer,the wedge locks the post.

Another is allthread rod,pulling in tension.The main advantage here is that the "action" is only slightly based on the rod being straight.Translated,you can bend the rod to clear an obstruction and still have it work it's magic.Further reading.....pre-stressed concrete beams.

We generally try to design around these problems(just say no,haha).....but this happens in Church world so frequently that over the years many ways have been developed as a cure.Remember however.....you are designing for,"Drunks,small children,and old folks".Imagine a cpl of "sugared up" 8 y.o. twin boys jerkin on your rail section(newel post,etc) ,seeing which can "out pull" the other?Or an older person hangin onto it with all their might?Drunks can and do,even worse................

[Kent A Bathurst]

The basic framing I get, but making it so the top of the exposed end doesn't move it what I am concerned about.

I'm not sure what structure we will have under the floor, nor how much access we will have to it so longs posts or newel type lag bolts my not help.

Right now I'm leaning toward making it a glued and screwed torsion box assembly with a 1/4" skin and with the top plates extended into the wall and tied to a couple of studs.

do the basic framing, and then glue/screw 1/4" ply to both faces. I have a real hard time imagining that front edge wobbling............you have, in effect, a torsion box, no?

You could always go corner-to-corner between the frame parts, making a running-W pattern top and front. I can, have, and do over-engineer anything and everything, but even I have limits........;)

[scott vroom]

do the basic framing, and then glue/screw 1/4" ply to both faces. I have a real hard time imagining that front edge wobbling............you have, in effect, a torsion box, no?

You could always go corner-to-corner between the frame parts, making a running-W pattern top and front. I can, have, and do over-engineer anything and everything, but even I have limits........;)

Kent, stiffening the knee wall will do nothing to reduce the risk of failure of the connection of the bottom plate to the subfloor. The preferred solution is to extend a board or better yet a post from the unsecured end of the wall through the subfloor and secure it to either a joist or joist cross blocking.

[Rich Engelhardt]

I've removed a couple of knee walls that were just nailed to the sub floor and nailed to a stud in the wall.

They did not come out all that easy.

HOWEVER ... being a typical wood worker & always having the urge to over engineer any and everything, ;) ,,,,,I'd probably use 2x6 framing and two layers of 3/8" drywall hung in opposite directions to skin out the wall.

Once the skins (drywall) go on, that framing gets plenty strong. Just take the drywall all the way down to the floor.

[Halgeir Wold]

Unless the wall is made very thick, - like 6 to 8", it will be wobbly, without support from above or below. A small angular piece at one end will certainly better the situation, but then again, how long is the longer section?

EDIT - just now saw your dimensions - 5' long and fixed in one end - 6" wide should be OK. Just make sure that the free end is secured at both long sides at least for the first foot or so.
I have staircase railing about 5" long on top of a small brick wall. The lower sleeper is bolted to the bricks with bolts in the top concrete...... you'd have to kick it real, REAL, hard to move it..

[Kent A Bathurst]

Kent, stiffening the knee wall will do nothing to reduce the risk of failure of the connection of the bottom plate to the subfloor. The preferred solution is to extend a board or better yet a post from the unsecured end of the wall through the subfloor and secure it to either a joist or joist cross blocking.

ok...now i see the point.

agreed


but - i can over engineer this also, with cross-braces inside the box - front upper down to a cleat at back lower; vice versa on the next "seat joist". you could build that thing offsite, set it in place, and fire a few anchors into the wall studs...........without any anchors into the floor.

[John Donhowe]

One more thought- if the design allows it, adding even a small "L" or "T" to the free end of the wall would add a tremendous amount of rigidity.

[Max Neu]

One more thought- if the design allows it, adding even a small "L" or "T" to the free end of the wall would add a tremendous amount of rigidity.
Yes it would,by adding a "T" or "L" bracket (I would run it all the way to the top) that would tie in the top of the wall to the floor,which would eliminate any concerns about the bottom plate/floor connection.As long as your not working on top of a finished floor,theres no reason you couldn't do this.I would route a recess in the sub floor for the bracket to sit flush,so it doesn't interfere with the finished floor when it get's installed.

[Edward Oleen]

off topic, kent: I understand the corollary - that makes a whole lot of sense. My question is: "What is the Theorem". and Just who is Larry?

[Kent A Bathurst]

off topic, kent: I understand the corollary - that makes a whole lot of sense. My question is: "What is the Theorem". and Just who is Larry?

Larry Edgerton

There are a couple related threads in the Lumber Yard forum. Excellent conversations, and sometimes decent humor. Including my Theorem of Tool Residency, which Larry immediately modified by deed, not word. [The Mods still watch the LY conversations, but only out of the corner of their eye.]

All for only 6 bucks. You'd enjoy it, and you'd pay a pittance of freight to support SMC as a Contributor. And - you would understand exactly what Larry's corollary means - because you don't at this point.;) :D