Well, it is, I can see from the crawl space. It's the sideboards that seem problematic. They look sort of easy to do, if you happen to have a table saw.

We used lots of caulk and paint. 😳🙄. It’s a basement, so not that big of a deal to us, at least not enough to spend lots of time and money fixing it all.

We are in the planning stages of refinishing our basement. Came across this where they painted risers white and added new treads (can purchae at Home Depot or similar stores) As per above you could simply fill in gaps and paint. Hope this helps.

I have always appreciated having handrails on both sides of basement stairs where space permits, and certainly at least one. Almost my only reason for ever going to the basement means I am carrying something, the stairs are usually steep, and it’s just nicer to have the security of a handrail. I think uncarpeted stairs are safer so long as you don’t gloss the surfaces of the treads.

Thanks for the advice. I might look into putting some random new tread on top as clementine said. I'm doing the entire basement in LVP, but the stair pieces are awfully expensive - all around 90-100/tread. And installers charge more for stairs as well.

I may try a little foam and a lot of caulk in that one gap and see what happens. If it'll hold enough for paint that would be ok for now.

Since the carpet looks in good shape, I assume you're not replacing it. But painting baseboards next to carpet is a fiddly proposition. You'll almost certainly get paint on the carpet. In my experience, it's easier to take the baseboards off, paint them and then replace. And if you do that, you can reinstall without that gap (it would be at the other end which might be easier to deal with).

It looks like you have a stringer and baseboard but no skirt board.

Underneath the carpet is almost certainly raw wood.

What kind of wood? Particle board, plywood, solid wood--pine, oak...?

It's the sideboards that seem problematic. They look sort of easy to do, if you happen to have a table saw.

You don't need & would not use a table saw to cut a skirt board. (If that is what you mean by 'sideboards'.)

If you plan to use vinyl on the stair treads, then you will need skirt boards to cover the gaps (which I assume are necessary with vinyl treads.) .

When the carpet comes off, come back & post another picture.

I did our basement stairs with the same LVP as our basement floor and then added nice stair nosing in a color from the LVP was easy to do and looks great and not expensive at all.

The estimates I just got for different brands are all around 3k extra for the stairs on a 5k job for 380 sqf. That’s insane. I’m probably going to put in less cheap looking carpet or look into DIY. From what I understand the problem with doing the stairs in LVP is 1) the outrageous prices for nosings and tread and 2) your ability to correctly cut said outrageous nosings and treads for your stairs, since it’s very rare for stairs to be totally regular. Screw one stair up, that’s another $100 or more down the drain…