Stair Horse Layout and Cutting
7. Choosing the Material: I try to avoid the standard 2x12 Douglas fir solid-sawn lumber for my stair stringers, and use Timber Strand 1-3/4-inch LVLs whenever possible.
8. Finish Floor Compensation: Although I have previously calculated the stair riser and tread, I double-check the finish floor thickness on the first and second floor. If there's a difference that will affect the first and last risers, I make needed adjustments. Now's the time to catch this common mistake.
9. Framing Square and Gauges: Use a quality framing square and a decent set of stair gauges for layout. My stair gauge of choice, hands down, is the long-style L.S. Starrett model ST-SGF-111.
10. Marking Treads and Risers: A thick pencil line isn't the best for accuracy; I use a scratch awl to mark out the locations of my treads and risers. I lay out more treads and risers than needed, which allows for proper detailing of the top and bottom riser. I count out and number each riser and tread, making sure there is always one more riser than the number of treads.
11. Calculating Deductions: The bottom riser must always be reduced in height by the thickness of the tread. This allows the first step to conform to the rest; otherwise, it will be taller by the thickness of the tread. The cut is made on the level part of the stair horse that sits on the deck. When I make my plumb cut at the top of the horse where it will sit against the header, I remove an additional thickness equal to the finish riser material. Then I don't have to pad-out the framing when I attach it.
12. Laying Out Your Pattern: Once you've cut and tested your first stringer, use it as a pattern to mark the other stringers, like you would do with a rafter pattern.
13. Cutting: Cut close to, but not past, your layout lines, and finish your cuts with a sharp hand saw. Over-cutting can weaken the stair horses.