How to Build Stairs for a Deck

Stair building can be one of the more complex aspects of your deck project, primarly because it is an exercise in geometry and precision. One of the keys to being successful with your stairs is to take accurate and detailed measurements and then fully document them on a layout drawing. Once the layout and measurements are complete, construction of the steps should be completed with deliberate attention to detail in order to make sure you will be successful on your first attempt.

  • Tape measure
  • Level
  • 2-by-4 board
  • Stair posts
  • Cement
  • Post anchors
  • Framing square
  • 2x12 (stringer boards)
  • Drill
  • Lag screws
  • Metal thread cleats
  • Hammer
  • Hanger nails
  • Angle brackets
  • Silicone caulk
  • Circular saw
  • 2-by-6 boards

Measuring Layout

Determine the number of steps needed by measuring (in inches) the distance between the surface of the deck and the ground. Divide that number by seven, which is the average vertical rise for a step. Round the result to the nearest whole number to determine the number of steps needed.

Divide the overall distance between the surface of the deck and the ground by the number of steps previously determined. The result will give you the exact rise between each step.

Determine the step run for the stairway, which is the vertical distance between two steps. Typically, for stairs made of 2-by-6s, the run is 11-1/4-inches. Then, the span (or horizontal length of stairway) can be determined by multiply the run by the number of threads (or number of steps minus one).

Constructing the stairs

Based upon the layout design, determine the location for stairway stringers and posts, making the mark with the framing square. Locate the footings so they are 18-inches back from the span.

Make a mark on the ground using a 2-by-4 placed level and suspending a string with a plumb bob on the end. Dig holes where marked and pour concrete footings for the posts. Attach the posts to the footings using metal post anchors.

Measure the layout for the stair stringer (or side walls) using the run and rise previously calculated. Use a framing square to make square and accurate markings. Once the rise and run are marked, to back and draw the thread size for each step on the board.

Drill the metal cleats into the stringer board using lag screws such that they are flush with the bottom of each thread. Nail angle brackets to the upper ends of each stringer with hanger nails so that they are flush with the end of the board.

Place the stair stringer on the deck's side board so that it aligns with the outlines previously marked and is in alignment with the surface of the deck. Nail the other side of the angle brackets to the deck with hanger nails.

Attach the stringers to the posts by drilling a pilot hole and then screwing a lag screw and washer into the post. The screw head should be sealed with silicone caulk in order to lock it tightly in place.

Cut 2-by-6 boards with a circular saw at the width to fit between the stair stringers. Place each step (or thread) onto the thread cleats so that the front aligns with the outline drawn onto the stringer. Attach the front of the steps to the cleats using lag screws.

Tips and Warnings

  • Pre-notched and pre-cut stringers can be purchased at most hardware stores, which reduces the amount of time required for measuring and cutting stringer boards with brackets.

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