OSB treads and risers? Just to let you know: when I worked for a builder we would never build garage stairs properly [2x8 treads. (2) 2x4 risers], but still not as cheap as OSB treads and risers. Homedepot has a stair kit that you can put over this stair... You need to post pictures, because may be just redo whole thing with premade stringers will be easier and faster and to code.

Thanks. It's totally to code. The cheap OSB treads/risers were put in at my request as a stop-gap measure until we decided how to finish the space. There are three stringers, it's a very well-built barn :)

I'm putting pine flooring in the upstairs (it's a barn, after all) so I bought pine treads at HD and intended to use pine 1x risers.

I'll take pics in a bit and post them.

Why don't you remove the OSB stairs and install a pine one made by a stair company to your specs. They cost like $150.

@Horseback Rider Hmm. What costs $150? Do you mean all of the treads and risers? That can't be possible! (That would be awesome if true though.) What sort of company does this?

I'm thinking that may be what my builder assumed I would do. The rise of most of the stairs is 7 1/2". The top has a 7 1/4" rise. If my treads are 1" and the flooring we install over the subfloor is 3/4", I think that evens out that rise -if my math is right!

What sort of flooring will be at the top and bottom of the stairs, and on the landing? Whether or not these stringers are correct depends on the floor heights at top and bottom.

Those stairs look like they are ready for carpet. The overhang on the tread is common for carpet installation. If you want something rigid on the stair, you will need to take off the overhang.

I bought a utility type straight run pine stair (pine treads and stringers and OSB risers) to go down to my basement and it was $150. That was ten years ago so let's throw in $250 for today. There are companies that just make stairs. That's all they do. Plain one's, fancy one's, curved ones, angled one's, pine one's, Brazilian teakwood one's, etc. Keep your landing, have them come out and measure and they'll make the two stairs.

It all depends on the height of the OSB relative to the finish flooring at the top. It sounds like you've answered your own question.

The OSB should be removed to maintain the proper rise. You will need all the trimmings, along with relocating your newel post to accommodate the side boards.

Start by installing all the side boards, risers. This will determine the size of your treads.

May be this will work, looks like bottom thread distance is less than next... You will have to cut out the overhang..

https://www.homedepot.com/p/Stairtek-0-625-in-x-11-5-in-x-36-in-Unfinished-Red-Oak-Retread-XBTRO1136/202018662

No greadovers. They are nothing but problems. Remove the OSB and put on real treads and risers.

I don't like the way the stringers are cut and attached to the mid level landing. Both lower and upper runs.

It actually does look like 3/4" OSB might have been used based on the photos, so a change to 3/4" in another material shouldn't create a dimensional change. If you put another material on top of that though and the stair wasn't designed for it you may have a problem.

Jeffrey Grenz, I agree. Especially the lower run. It appears that the lower stringers are attached to a sheet of OSB which is then attached to the landing. You have screws running in opposite directions top and bottom and a connection in the middle that is only as strong as the sheet of OSB.

Agreed. The lower stringers look as if they are completely dependent on a single piece of OSB used improperly. The upper stringers are supported by a single nail on the bottom and a notch towards the top. The notch is on the upper side of the stringer, which is also "V" cut for each thread/riser, in other words the non structural side of the stringer. Both the upper and lower stringers need better support.

Stair isn't built to code. Even in areas when permits and licenses aren't required, code prevails. This would be a heavily used stair. Pay attention.

I prefer carpet when coming into the house from a garage... cheap shoe cleaning short loop carpet. But if you prefer the look of scratched Oak...

Those stringers! They can not be unseen!

The very least that should happen, laminate with plywood bottom stringer part from both sides.

The guy who cuts those stringers does so with the finished floors in mind. If the stringer has been cut for a 1 1/2" rough tread, then that's the thickness that has to be installed to meet code. You can lay some OSB treads down temporarily, but unless the stringers were cut for that finished thickness in mind, the treads aren't to code.