How to Build Stairs in 3 Easy Steps

Building a staircase, even a short one, isn't simple. It requires precise measurements and some careful calculations. Here's how.

How to Build Stairs in 3 Easy Steps
American Artist

From a technical standpoint, there's nothing particularly difficult about building stairs for a deck, porch or shed. Anyone with basic carpentry skills can make the necessary cuts and assemble the parts. And yet, stair building is arguably the most challenging task do-it-yourselfers will ever attempt.

Stairs must satisfy strict building codes meant to ensure safety and climbing comfort. We're so used to uniform, professionally built staircases that the slightest discrepancy between steps creates a tripping hazard. Tall steps make climbing hard. Shallow steps are uncomfortable and dangerous. Since there's so little room for error, building stairs requires careful layout and some potentially tricky calculations. Start by consulting your building codes office for local guidelines. Then, follow the procedure laid out on these pages--taking plenty of time to plan correctly. We used steps leading to a backyard deck as an example.

Basic Stair Anatomy

There are three main components in a typical staircase: stringers, treads and risers. Stringers, typically cut from 2 x 12s, are the sloped boards that support the other components and carry the weight of people walking on the stairs. They're typically spaced 16 in. on center. When determining the staircase width, remember that wider is better. "Wide staircases are more comfortable and safer to walk on," says remodeling contractor Paul Mantoni, of Exteriors Plus in Terryville, Conn. "I seldom build one less than 4 ft. wide, and prefer them a bit wider."


Treads form the top surface of each step, and risers are installed directly under the front lip of each tread. Some stairs don't have risers, but that's a mistake, according to many builders. "Risers protect the exposed endgrain of the notched stringers from the weather," explains award-winning deck builder Scott Padgett, of Idyllwild, Calif. "Without risers, stringers will crack or split much sooner."


Step 1: Calculating Rise and Run

The first step in building stairs for a deck is finding the total rise or overall vertical height the stairs have to cover. Lay a straight board on top of the deck, extend it from the edge, then measure down to the landing location. Let's say the total rise is 57 in. The next job is to find the rise of each step. Divide 57 by 7 in. (the typical rise per step) to get 8.14. Round down to get the steps: eight. To then determine the actual rise, divide the 57 in. by the eight steps to get 7 1/8 in. per step.

You can use that information to find the total run of the staircase--or how much horizontal distance it will cover as it climbs. Multiply the number of steps by the run, or horizontal depth, of each step. The optimum run of each step is no less than 10 in., which is enough space to accept two 2 x 6 treads. In our example, the staircase has eight steps, so the total run is 80 in.

There is one wrinkle in the math, however: If you are working with a tall deck, it's a good idea to break up the staircase with intermediate landings. "As a practical matter you're limited to about 14 steps because that's the most you can cut [in a stringer made] from a 16-ft.-long 2 x 12," says Andy Engel, author of Building Stairs (Taunton), "but I prefer adding a landing after every seven or eight risers."


Step 2: Cutting Stringers

Before laying out the steps on a 2 x 12, decide how the stringers will join the deck. They're either attached directly to the rim joist so the top step is flush with the deck top, or to the framing under the deck, which is the way we did it (see drawing on previous page). When mounted under the deck, the stringers are either attached to the joists or to blocking placed between joists, and the stringer ends are cut long to reach the framing.

Mark the tread notches using a framing square fitted with stair gauges. These small brass fixtures clamp onto the square, providing an accurate way to mark several identical notches. Clamp one stair gauge on the square's tongue directly at the rise dimension. Attach the other gauge to the body of the square at the run dimension. Then, lay the square on the 2 x 12 with the gauges pressed against the board's edge and mark the tread and riser. Slide the square down, align it with the previously drawn notch, and add the next one.

Cut the notches using a circular saw, being careful not to go beyond the lines. Finish the cuts with a jigsaw or a handsaw.

Next, trim the bottom of the stringer an amount equal to the tread thickness. For example, if you're installing 2 x 6 treads, cut 1 1/2 in. from the bottom of the stringer. Use the first stringer as a template to mark the remaining stringers.

We screwed each stringer to the deck-frame blocking, which was spaced 16 in. on center. With the stringers in place, check that each step is level, and use a block plane to shave down high spots.


Step 3: Installing Treads and Risers

Cut the risers to length and fasten them to the stringers with 2 1/2-in. trim-head decking screws. Note that we cut the risers and treads to overhang the outer stringer by 1 1/4 in. Later, a 1 x 12 cedar trim board will be nailed to the stringer, giving the staircase a more finished look. This detail isn't always necessary.

After installing the risers, fasten the treads with screws. Leave a 1/8- to 1/4-in. space between the treads. Continue installing treads, working your way up the staircase. The 4 x 4 posts used to support the stair rail are typically bolted to the stringers before installing the treads. However, we completed the stairs first, and then attached the posts and built the handrail that codes usually require.

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