After talking to many deck builders over the years, we have found that stair construction is considered the most difficult part of building a deck. In order to find the right stair stringer layout for your stairs, you first need to measure the exact height of the deck from the top of the decking to the location where the stairs are going to land on the ground. You will need to remove the thickness of the riser board from the top stair and remove the thickness of the tread board from the bottom stair. You can now draw the notches for the stairs onto your 2×12 stair stringers. The difference between the stair rises and tread depths cannot vary by more than 3/8″ from the largest to the smallest.
Deck Stair Stringers Spacing
The load supporting requirements for stair treads are more severe than for the rest of the deck because the force exerted by a person walking downstairs is a more intense blow to the surface than a standard stride across a level surface. Because of this, you should never space your stair stringers more than 16” on center. This means you will need to install a minimum of four stringers on any stairway wider than 36”. Always check the maximum span for your decking material as it applies to stair treads.
Some composite materials and lower-grade 5/4 wood decking may require you to reduce the stringer spacing to 10” on center. Always read the composite decking installation instructions for stair treads before building your stairs. It is best policy to overbuild your stairs because of the increased wear and tear they often receive. Pay particular attention to the stringer placement if you are attaching stairs around a corner, as in the case of a cascading staircase.