To frame a deck stairway, you need to figure out the number of treads (steps) required and the rise and run (depth) of each tread.

First, measure the height of the deck.

Then divide the height by 7 (a typical stairway rise). If the answer's a whole number, then that's the number of treads you'll need.

If the answer ends in a fraction, then round it off to the nearest whole number. That'll be the number of treads. Divide that into the height. That gives you the rise you'll need for that number of treads.

To determine the most comfortable run of your treads (the length), divide the rise into 75. So with a typical rise of 7 inches, a typical run might be 10-1/2 inches. A rise of 7-1/2 inches would work best with a run of 10 inches. But this so-called "comfort formula" does allow some leeway, so layouts of 6-12 (72) and 7-11 (77) work out fine.

TIP: On deck stairs, a run of 10 inches always works great because you can use 3 2x4's (for a total width of 10-1/2 inches wide) or 2 2x6's (11 inches wide) for the treads, leaving a nice 1/2-inch or 1-inch overhang at the front of the tread.

 

Laying out Stringers
You can lay out a stair stringer very quickly with a framing square by finding the rise on one leg and the run on the other leg and then lining those up with the edge of the board. Mark along the edges of the square to create the first step. Then move down the board, line up the square and draw the next step. Continue that until you've drawn all the treads.

 

Cutting Stringers

Use a circular saw to start all the cuts.

But use a handsaw to finish them, since the circular saw blade leaves a little bit uncut at each corner.

 

Tracing Stringers

TIP: All stairways require at least 2 stringers, and taller or wider ones require 3. (Always check with your local building department.) But rather than lay each one out individually with the framing square, cut the first stringer out and use that one as a pattern for the others.

 

Bracing Stringers

You can install each stringer separately, but it's usually quicker to connect them together with braces before setting them in place.

Notch out each stringer for 2x4 braces at the top, middle and bottom.

Screw the braces in to each stringer.

 

Attaching Stringers

Set the stringers in place against the rim joist and nail through the top brace into the rim to hold it.

Lag screw through the brace into the rim joists to secure them permanently, pre-drilling for each screw.

Installing Treads

Cut the treads to fit over the stringers, leaving a 3-quarter inch overhang on each side to serve as a drip edge and keep rain from dripping down onto the stringers.

Screw or nail the treads down into the stringers to finish the stairs.