Is it possible to bend the wood across its width? If so, how? Or do I need to simply lay the boards parallel to the deck and then trim the ends?
Alcoa Vinyl Siding
Your stair boards that sit on top of the stair joists just need cut to shape. Also your stair joists will need cut to the correct shape to provide support under each stair board. I’d probably recommend using three stair joists. A long one in the center and two shorter ones on the ends. Then if you want to add a finish trim underneath the stair boards, that you will have to bend. That is normally done by steaming the board then bending it around a form that bends the ends slightly more than what they will be bent on your stairs. Then pin your board in place after bending it around the form and let it sit for a while gain the bent shape. Once you release it from the form it will bend out some, just like a spring would. Then just nail your bent trim in place. Remeber on your stair joists to account for the trim width if you are going to add trim.
The way through the board with circular saw made about every half inch depending on how tight abend the back of the most part but you will need to be bent if they dont bend easily or if they dont bend.
The badk of the boards to make.