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How to Build Stairs

Three Parts:Making the Preliminary MeasurementsCutting the StringersAssembling the Staircase

Stairs are essential building blocks of any two-story construction projects. Stairs are constructed of three main things: stringers, treads, and risers. Stringers are the diagonal 2x12s that carry the weight of the people walking up the stairs. Treads are the top baseboards onto which you step, and risers are placed perpendicularly under each tread. With this information, you're ready to begin building. See Step 1 below for a detailed guide on how to bring a set of stairs from concept to execution.

Part 1
Making the Preliminary Measurements

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    Measure the height of the area where you will install the stairs. This is also called the total rise. If you don’t plan to make the top step level with the area where the stairs begin (ex. deck, doorstop, etc.), be sure to account for this gap in your measurement. Be sure to measure from framing to framing.
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    Divide the total rise by the typical rise per step. This will give you the total number of steps on your stairs. The typical rise per step is about 7 inches (17.8 cm), but you'll probably use a different height in your final construction. (See below for a handy rule of thumb.) If your total rise is 95 inches (241 cm), divide it by 7 inches to get 13.53. Round down to get the number of steps: 13.
    • The rule of thumb for treads and risers is that the sum of each should equal between 16 and 18 inches (40 and 45 cm). So, if your riser is 7 inches (17.8 cm) tall, your tread should be anywhere from 9 to 11 inches (23 to 28 cm) long. This makes the treads long enough to comfortably fit the average foot on and high enough to make stepping easy.
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    Divide the total rise by the number of steps to get the actual rise per step. To continue with our example, divide 95 inches (241 cm) by 13 steps to get 7 and 5/16 inches (18.5 cm). On your stringer, each step will rise 7 and 5/16 inches.
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    Establish the run of each step to get the total run of the staircase. The run of each step should be no less than 9 inches (23 cm) and realistically at least 10 inches (25 cm). Multiply the total number of steps by the run of each step: 13 total steps x 10 inches = 130 inches (330 cm) total run. The total run is the horizontal distance the stairs will travel from beginning to end. In our theoretical example, the total run is 130 inches.
    • If you intend to build a long staircase, you may need to install landings every so often. Since the longest boards you will be able to find that are appropriate for this project will probably be 16 feet (4.88 meters), you will probably max out at about every 14 steps; however, you can install landings sooner if you prefer. If your staircase will have landings, considering each section of stairs as its own mini staircase will help you follow the steps below.
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    Calculate the length of the stringers. The stringers are the pieces of wood that will run diagonally underneath the length of the steps to hold them up; these are what your steps will eventually be attached to. Determine their length the same way you determine the hypotenuse of a triangle in geometry:
    • Multiply the horizontal length (run) by itself, multiply the height by itself, and add the two results together. Then, find the square root of this sum.
      • sqr(130 x 130) + (95 x 95) = 161 inches (409 cm)
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    Determine how you will attach the stairs to the existing structure. If the stairs will sit flush with the vertical face of the structure, you need only look for places to either directly attach your stringers to the existing framework or add supports that will link the stringers to the existing framework. However, if the stairs won’t sit flush with the existing structure (such as if they will attach to a deck with an overhang), be sure to either create a secondary support system or modify the tops of your stringers accordingly.
    • If the stairs will mount beneath an overhang, making sure that the top step isn’t level with the top of the structure will simplify the process.
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    Determine how many stringers you will need. To prevent your steps from sagging or bowing as you step on them, a wide staircase will need plenty of stringers underneath to keep it evenly supported. For safety reasons, the stringers should be spaced between 16 inches (40.6 cm) and 4 feet (121.9 cm) apart. A very narrow staircase might be able to get away with having only two stringers, but it’s best to start at three and work your way up as necessary.
    • Wider staircases are almost always preferable to thinner staircases because they are much easier and more comfortable to navigate. If possible, elect a wider space for your staircase and shoot to use at least three or four stringers.

Part 2
Cutting the Stringers

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    Lay out a sufficiently long piece of 2x12-inch (5cmx3m) lumber. Don’t cut it down to length just yet; it will sit at an angle that depends on the height and depth of your steps, and the ends will have to be modified.
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    Mark a framer's square to the height and depth of your steps. In our example, you would need to mark it at 7 and 5/16 inches (18.5 cm) on one side by 10 inches (25 cm) on the other. Be sure you know which side corresponds with the height and which side corresponds with the depth to keep from ruining your measurements.
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    Modify the top of the stringer to account for the overall angle. This angle will depend on the size of your steps. Be sure to account for any modifications (ex. added length when mounting beneath an overhang) if necessary.
    • Place the carpenter’s square over one corner of the lumber. Lay the side marking the height along the end of the lumber and the side marking the step depth along the length of the lumber.
    • Draw a line across the lumber from the step-height to the step-depth mark on the square. This line marks the horizontal top of your stringer.
    • Mark the line so that its length is equivalent to the depth of one stair. Start from the end of the existing line that is closest to the center of the board, measure outward, and mark the spot.
    • Use the square to draw a line perpendicular to the spot you just marked. This line marks where your stringer will sit flush with whatever you’re attaching the staircase to.
    • Cut along these lines. The top end of the stringer will now fit to the attachments at the appropriate angle.
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    Measure and mark each step along the piece of lumber. Using the horizontal top of the stringer as a reference point, measure down a distance equal to the height of one step, across a distance equal to the depth of the step, and so forth until you’ve drawn the necessary number of steps.
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    Use a circular saw or hand saw to cut the step-notches into the stringers. If using a circular power saw, cut to the edge of the marks then use a hand saw or jigsaw to complete the cut. Stop saw cuts 1/8 inch to 1/4 inch short of the opposite lines.
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    Square off the bottom of the stringer so that it will sit flush with the ground. To cut off the protruding bottom corner, simply mark and cut a line parallel to the top of the last step.
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    Test the stringer by setting it in place. Make sure the height is accurate.
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    Use the first stringer as a template off of which to base the next stringers. Lay the first completed stringer down on a 2x12 and simply trace the outline of the first stringer onto the 2x12. Then cut as necessary.

Part 3
Assembling the Staircase

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    Install the stringers. How you attach the tops of the stringers to the structure will depend on the structure’s surface, overhang, etc., but one way is to nail metal joist hangers to the floor joists. Only joists made with 2x12s (or bigger) provide enough surface area for mounting brackets. Set the bottoms of the stringers on a firm footing like concrete, wood flooring or concrete blocks if in soil.
    • If sitting on concrete, set the stringers on tar paper to prevent the rotting of the wood due to moisture.
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    Secure and stabilize the stringers by installing risers, or toe boards (optional). Toe boards usually are made from 1x6-inch (2.54x15.4 cm) wood. Though you can do without them, screwing these planks vertically between each step will look nicer, last longer, and protect the end grain of the cut stringers.
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    Cut and install the risers. Cut the riser material to length and secure across each stringer with 2 1/2 in. (6 cm) screws.
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    Cut and install the treads. Cut the tread material to length and secure it to the steps of the stringers with 2 1/2 in. (6 cm) screws. If you wish, cut the treads so that they overhang the stringer just a bit.
    • For an extra flourish, measure the necessary depth of each step (plus overhang), divide it by half, and cut each board to this width; you can then install two boards for each step.
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    Fit any trim board underneath the overhanging tread and nail to the riser. If you want your stairs to have a little bit more class, you can install trim boards cut to length of the tread and install them right underneath.
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    Varnish, paint, or seal your steps if necessary. If your stairs are outdoors, especially, consider treating the wood against the elements. Even if you're building indoor-use stairs, consider treating them to safeguard against everyday wear and tear.


  • Remember that interior stairs require better quality wood and will need to be cut extremely precisely.
  • Using a pair of stair gauges on the carpenters square will assure consistency of you layout.


  • When measuring the height of the stairs, be sure that you measure from the bottom of the floor deck or top of the floor joist.

Things You'll Need

  • Circular saw or crosscut hand saw
  • Carpenter framing square
  • Framing hammer
  • Corded or cordless drill
  • Nails and screws
  • Metal floor joist hangers
  • 2x10-inch (5.1x25.4 cm.) planks for stringers
  • 2x6-inch (5.1x15.4 cm.) planks for steps
  • 1x6-inch (2.54x15.4 cm) planks for toe and foot boards

Article Info

Categories: Home Improvements and Repairs