PT Lumber staircase question
I will be replacing a long floating staircase as part of my deck project. It needs approximately 16 foot 2x12 stringers. Being that long and being a staircase, it is important that the lumber be dimensionally stable. If the boards curve as they dry, it would be a disaster. Any advise or rules in buying Pressure treated lumber for the stair stringers?
Stairs will be 3 feet wide. Planning on doing a solid outer stringer nailed to an inner stringer on both sides. Inner stringer will be either of two methods:
1) stair steps cutout with step boards screwed down into this stringer.
2) cut out a 2"(1.5" really) notch and slide in step. End nail step surface from outer stringer.
Any advice on pros and cons of either of these approaches?
Deck step surfaces are 2"x10" ipe. So steps are strong enough for the span. A cut center stringer would add little strength given the amount that would need to be cut out of it. Step tread not as deep as wanted, but limited by location of staircase. Can not fit a longer staircase, so have to replicate rise and run of existing.