I recently removed the sheetrock on an interior wall, and noticed a diagonal piece of wood. Is it ok to remove it and replace it horizontally with 2x4/2x6? I simply want to open up the wall to make use of natural light. Photo included.
Thanks for advice.
It is not ok to remove anything from that wall without further investigation.
Based on the available evidence, which to be fair isn't authoritative, you should not proceed. Usually, the answer to a photo of some studs and "is this a supporting wall" is "we can't tell".
But there is a lot of evidence in your photo that this is probably a supporting wall, and since the question is "can I remove parts of it" the answer is "No!".
The triple stud and the jog in the ceiling height both suggest there is a beam at that point in the ceiling, and these studs may be supporting it. The very existence of this wall in an otherwise open plan suggests it was placed to avoid a longer, and perhaps more difficult and expensive, beam. The way that diagonal brace is cut into the studs suggests it is performing some structural task.
None of that is authoritative, any or all of it could be wrong. But I can say with confidence that until you have a lot more evidence to the contrary you should not remove any part of this structure.
The diagonal 1×4 is "let-in-bracing" (LIB). See IRC R602.10.4. It's a structural part of your house's lateral system for resisting wind and/or earthquakes. In line with this LIB there should be one or more additional LIBs, where together the line of LIBs form a "wall brace line." Removing an LIB from this wall brace line is nontrivial, especially if you're in an earthquake zone. You should expect to find similarly detailed wall brace lines every 25 ft or less if you live in a D seismic design category (see IRC R602.10.1.3). For regions with less seismicity, the bracing at your location would probably be supplementing the wind bracing at the ends of your house because there was too much paneling displaced by doors and windows.
Finding a narrower wall bracing type in the IRC to swap for your LIB won't easily solve the problem. Mixing bracing types in a braced wall line would still require the narrower wall bracing type to use the offensive LIB's width (see item 3 under IRC R602.10.4.1), and that's assuming that your loading type and intensity even allow mixing. To narrow things down with an alternative brace type can require finding all of the LIBs in the brace wall line and then converting and/or removing all of them. For the special case of low seismicity regions, you could mix bracing types and install a minimum width brace at your offensive location. This would require additional bracing installed elsewhere along the wall brace line to make up for the net loss of bracing.
Depending on your house geometry, it's possible that you can install an equivalent LIB elsewhere along the brace wall line to eliminate the offensive brace. Unfortunately there are brace location constraints along brace wall lines, so this is unlikely. See IRC R602.10.2.2. There are more stringent requirements in R602.10.2.2.1 if you're in a D seismic design category.
I noticed that you were receptive to comments suggesting that you can poke all sorts of holes in this wall for aesthetic purpose. Unfortunately, 1/2" gypsum board on the wall face opposite of the LIB's 1×4 is a structural requirement. See IRC R602.10.4.3.
I doubt that the brace is important. Here's my reasoning:
It's in a short wall at a steep angle. Realistically that's not going to prevent calamity in a tornado.
There seems to be plenty of redundant support in the nearby walls and roof structure.
That type of brace isn't used anymore. It's possible that it was put in by an old-school carpenter just because that's how we've always done it.
I make a few assumptions:
That the brace terminates at the floor and ceiling, thereby not providing more support than is seen here.
That there's no beam on the triple stud. (That pertains more to removal of the stud, but the diagonal brace would have more purpose if there is a beam there.)
That you have a reasonably modern, well-designed roof structure. Such a structure transfers a lot of lateral load between walls and would further make this brace redundant.
Related: