How to Design a Beam in a Stair Case

Measure the height from the floor or ground in inches directly up to the spot that the top of the staircase must hit. If you cannot make this measurement against a wall due to obstacles, measure as far out from the wall as necessary so that you can measure straight up and use a level to make sure that the measuring tape is sitting perfectly vertical.

Divide the staircase height that you measured by 7 inches, the average rise for each stair in a staircase. Round the quotient up to the nearest whole number to determine the number of stairs that you should place in the staircase. Divide the original height that you measured by the number of stairs to determine the exact height of each stair.

Measure out from the base of the wall against which the top of the staircase will sit to the spot on the floor where you want the staircase to begin. Start a scale drawing by drawing both the height of the staircase and the length of the staircase. Then connect the end points of the two lines to make the sloped line that represents the actual path of the staircase. Place a protractor at the spot where the top of the staircase height meets the top of the sloped line and measure the angle.

Check local building codes to make sure that the angle of the staircase meets building requirements. Obtain local buildings codes from either your local government’s building office or from the local government’s website. If the design of your staircase is too steep, you must start the staircase further out on the floor to provide a more gradual slope to the staircase.

Measure the length of the sloped section of the scale drawing once the drawing meets codes. Translate that scale into an actual number, just like the actual height and length of the staircase. Get a beam approximately 6 inches longer than this length.

Place the top of the beam against the upper floor that it needs to touch and the other end of the beam against the lower floor. Use a circular saw to trim the beam away at each of these locations a little at a time until the beam sits flat against both surfaces. Remove some length of the beam if necessary to accomplish this.

Find the height that you measured for each stair on one arm of a carpenter’s level. Place a stair gauge at this spot. Place a stair gauge at roughly 12 inches on the other arm to serve as the width of each step.

Start at the top corner of the beam that will support the top step of the stair case. Line the stair gauge that marks the height that you determined for each stair up with the corner and slide the level back until the second gauge sits flush against the beam. Make the “V” created by the arms of the level where they touch the beam with chalk.

Move the level down so that the first gauge lines up with the end of the last mark and repeat the process until you have connected “V's" all the way down the beam. Go to the other side of the beam and repeat this process so that you have guides on both sides.

Cut the marked sections of wood out of the beam with a circular saw and create a notch for each stair. Secure the notched beam to the upper and lower floors using four bolts long enough to pass through the wood of the beam and into the surfaces at each end.