If it's your own house, I would replace treads and risers. The pre-fab treads are great because you can prefinish them, so it's less of a mess installing/finishing them (IF you're going over old 5/4 treads. If they're 2x then it's a toss-up because you have to cut off the front). IMO the prefabs aren't nearly as good as solid wood treads. JM2C