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I am trying to install a couple of windows in the knee wall of my house. The knee wall is 4' high trying to get a 32" x 42" window in. I was wondering if I could cut out the 2 top plates so I could get a header in. Any help would be great.
 

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Kneewall or cripple wall? A cripple wall at the foundation level is a shear wall believe it or not and the framing and sheathing have value. I wouldnt cut out a window much less the plates.
 

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I'm not sure that you're really talking about a knee wall. If you're talking about a cripple wall, then the answer is absolutely not. Google "cripple wall failure" and you'll see a bunch of examples of why not to mess with them. If you are talking about a low exterior wall on a story-and-a-half house, well I guess that is technically a knee wall, and you shouldn't mess with the plates on that either because your roof is resting on it. But what I think of as a knee wall is an interior wall in the attic, and I don't really know why you would want windows in it, and the roof is bearing on it anyway, so you probably shouldn't mess with it.
 

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Depending on what exactly your are trying to accomplish, I have designed stuff similar to what your describing by cutting out the top plates, inserting a proper sized header and tying the two ends of the top plates into the header with MSTAs from Simpson.
I like that particular one as it is 18 GA. not too expensive and does the job.
Placed on both sides of top doubler.
Not telling which size as I am not your designer, so there.

Andy.
 

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I'm envisioning a split-level... with 4' stud walls from the top of the poured wall to the bottom of the upper floor framing...... OP pics help a ton.
 

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What you are proposing, in spite of your terminology, can be accomplished, probably much like Andy described.

However, an Engineer must examine that particular component of the wall and evaluate it as to how it relates to the entire structure. Upon completion he will provide you with the appropriate means to accomplish your request.

This sort of project should not be completed, by a bunch of arm chair engineers with a lot of by guess and by golly theory....:laughing:
 

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ScipioAfricanus said:
Depending on what exactly your are trying to accomplish, I have designed stuff similar to what your describing by cutting out the top plates, inserting a proper sized header and tying the two ends of the top plates into the header with MSTAs from Simpson. I like that particular one as it is 18 GA. not too expensive and does the job. Placed on both sides of top doubler. Not telling which size as I am not your designer, so there. Andy.
I've framed it that way many times, zero top plate. The straps takes the scissors points out of it.
 

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4' wall, 42" window, that's not giving your engineer much room to work with. What's the specific situation? Pictures? Something magical about the 42"?
 

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If what you call a knee wall is a short wall from the foundation to the underside of a subfloor, you could possibly raise the header into the floor cavity to accommodate the proper sized header. Six inches isn't enough room for a wood header unless there is virtually no weight on the window. A steel beam is always a possibility if you can bear the posts carrying it down to the foundation.
 

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There's more than one way to get that done.

In any case, an engineer will need to have final say on design.

You can drop a header in on top of the plates from above and hang the rafters from it.

You can build a header at the fascia line and use upside down hangers to hang the header from tails with solid bearing. You're going to need to go a couple rafters beyond each side of the opening.

Depending upon field conditions, you could set a beam on top of the ceiling joists, being careful to transfer load down to solid bearing at both ends.
 

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I never understood why they call them knee walls when most of them are 42" tall?
 
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