How to Do Stair Trim Molding

Floor moulding and trim flows from ground floor to upper floor by following the contours of the stairs. Moulding along stairs follows vertical and horizontal seams, which makes installation complicated due to the amount of angles needed. Mounting and cutting stair moulding is the same process as cutting normal moulding, except for the measurements of the angles. The cuts are more complex as you will be angling the wood into the miter saw, as opposed to angling the saw blade.

Chair rails on stairs require measuring the angle of incline of the stairs.
  1. Measure the height of the first stair where it meets the wall. Measure from the floor to the top of the top corner of the step. Use an angle finder to verify that the step is 90 degrees.
  2. Place the mark for the measurement on the trim to be cut with a pencil. You will be trimming off both ends of the trim so place the mark a few inches from the end of the piece and measure from that mark to the height determined in Step 1. Place a second mark at that point.
  3. Adjust the plate on the miter saw, which is where the wood sits, to 45 degrees. Adjust to one half the angle of the stairs if the step was not 90 degrees.
  4. Place the wood into the miter saw with the first mark pointed at the cutting blade. Position the wood to the left of the saw blade. You will not be cutting on the mark, but where the mark meets the edge of the wood closest to the saw blade. This will cut the wood properly for a vertical strip of trim.
  5. Slide the wood forward in the saw so that wood sits to the right of the saw blade. Cut the end so that the end is also at a 45 degree angle. You want the wood to have parallel ends where you cut them.
  6. Install the trim by holding it in place and using a brad nailer with 2" brads to nail the strip into the wall.
  7. Repeat Steps 1 through 6 for the depth of the stair. Turn the wood over when cutting so that you are not cutting the face of the trim. This allows the cut to be made for a horizontal piece of trim. Repeat the whole process for each additional stair.

Things You Will Need

  • Miter saw
  • Angle finder
  • Measuring tape
  • Pencil
  • Brad nailer
  • 2" brads


  • Test the process on scrap wood before attempting with the actual trim. Use an angle finder to measure the angle of a corner if you have to wrap the trim around a corner and up the stairs. Adjust the angle of the saw blade to one half the angle of the corner to make those cuts. Otherwise, cut the strip the same as the remainder of the strips.

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