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I'm doing some prep/exploratory work before I begin finishing my basement. Home was built in 1980 and has a cement block foundation. There is a seemingly random wall framed in the otherwise unfinished basement. I pulled one side of the sheetrock - I was originally planning on demoing the wall completely to accommodate the layout I was going for. I was surprised with what I found: a "diagonally" framed wall with a pretty serious 4x6 header spanning about 12' across. This occurs at an outcropping within the foundation. The wall runs between the front of the home (flat wall, ~52' in length) and an outside corner. Obviously the wall is not carrying any vertical load, but rather it seems to perhaps have been framed to allow some horizontal load (to support the outside corner of the cement block foundation, perhaps?). Notice the about 16" into the cement block outside corner a steel beam that is supporting the middle of the home is resting on the top of the foundation (2nd pic).

Whether I leave the wall or not isn't a huge deal to my design, and I'd need to run some electric into it anyways, so removing one side of the sheetrock isn't wasted effort. I've honestly just never seen anything like this before (father was a general contractor, been in many homes getting framed during my early years). I'm thinking someone was just bored on the job one day, but would love some other opinions. One odd thing I noticed is that the black waterproofing paint/coating is present behind the vertical studs that are affixed to the cement block, meaning this wall wasn't there during the time that coating was applied. Another odd thing is that the 4x6 header appears to be much older than the rest of the framing, almost like it came off a different job site or something.

Anyone seen anything like this before?

Overbuilt basement wall

enter image description here

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    toss the concept of "shear wall" into your consideration. Nobody bothered with those diagonals becasue they were bored. Are you in a seismic hazard zone? Contemplate plywood rather than drywall when you re-sheathe the wall.
    – Ecnerwal
    Sep 7 '20 at 12:53
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    The architect / builders were definitely worried about something.
    – JACK
    Sep 7 '20 at 13:17
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    Perhaps it's a shearwall for wind code purposes? Are there signs of wind/hurricane code application (such as hurricane straps and anchor bolts) elsewhere in the house's framing? Sep 7 '20 at 13:20
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    Does that concrete block show any signs of bowing inward? Sep 7 '20 at 14:03
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    The fact that the 'inside' of the arrow was clearly made at a different time, seemingly more recently, as the rest of the wall is also something to factor when pontificating why it was done. Sep 8 '20 at 4:00
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This gives all the impression that is was designed and installed to support the basement wall that the "arrow" of the diagonal bracing points to. The vertical post against that wall is what was put there to support that wall.

The bottom of that post is most certainly held up against the wall securely by the bottom plate in that wall which is likely pinned to the concrete floor.

The top of post is held against that wall by having that large horizontal beam bear against the opposite basement wall.

The diagonal braces are keeping the center of the vertical post from bowing in. The studding fitted above and below the diagonals is placed there to keep the long diagonals straight so that they do not bend under compressive load.

You should carefully evaluate what is going on on the outside of the basement wall where that vertical post is located. There may be excessive ground pressure against that wall due to any number of reasons that can only be guessed at. In the evaluation also check the wall itself to see of there is evidence of cracked blocks, cracked mortar joints or overall inward buckling of the wall.

It is even possible, though not likely, that this wall support was placed there based upon past concerns that may not be obvious today.

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    That is probably the most logical explanation. You are correct that the base plate is pinned to the floor. I find it odd that they didn't affix this wall to the joists up top, still. I'll likely toss a few electrical recepticles in the wall while it is open and leave it intact otherwise. The wall is from the same time period as the original construction. Same drywall dated back from 1980.
    – cxd213
    Sep 7 '20 at 14:41
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    @cxd213 - Yeah the design of that construction is pretty serious and it was not done as some weekend hobby project. You would be wise to investigate the situation outside that wall of the basement to see if there is anything going on there that could lead to future problems along that block wall.
    – Michael Karas
    Sep 7 '20 at 14:48
  • I'd suggest that a key question is how those short lengths of 2x4(?) between the diagonal braces and the door frame are anchored, since if that brace is intended to resist lateral pressure a very large part of the force will be converted into shear between those lengths and the beam/base above and below. Sep 8 '20 at 9:13
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    It looks like Chesterton's Fence applies here: if you can't see a reason why something should be there, don't touch it. Only when you understand the reason why something is there, you may remove it. "It is even possible, though not likely, that this wall support was placed there based upon past concerns that may not be obvious today." might be the most important sentence in this answer. Sep 8 '20 at 14:13
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    Notice too that neither side is tied to joists. This was probably on purpose so that whatever horizontal forces that were causing issues at one time didn't start swinging the top. Not that if you have jack posts to hold wall and you tie the jack posts to joists that eventually when it gets too bad the joists will move and if this goes on too long can be devastating.
    – DMoore
    Sep 8 '20 at 20:58

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