Step 1: Height Chart to Make Your Ladder... or Find One in the Store
The problem with most ladders is that they accommodate people who are just under the 6-foot range in height because the ladder rungs are spaced 12" apart. Those of us who fall in the 5'3" to 5'9" (MOSTLY WOMEN) are miserable with that height.
The way to calculate how much ladder height we need to put us up there at the ceiling is by using 2 numbers: the first is your personal height with shoes on, and the second is the height of the average room where you will be working. In the States, most rooms are 8 feet which is 96 inches. My height is 5'5" with shoes or 65". Therefore the amount of ladder that I will need to reach that 8-foot ceiling with the top of my head is 96-65=31. Then we knock off another inch to keep the popcorn ceiling texture from crumbling onto our hairstyle. My ideal ladder height is 30".
Leaving an extra rung is the way to go. You will be more secure when you are not standing on the very top platform of your ladder. This chart indicates the height of the 3rd Rung, where you will be standing.
Ergonomic Ladder Chart:
Height: 5' 3" 3rd Rung: 32" 4-Step Ladder: 42 5/8"
Height: 5' 4" 3rd Rung: 31" 4-Step Ladder: 41 3/8'
Height: 5' 5" 3rd Rung: 30" 4-Step Ladder: 40"
Height: 5' 6" 3rd Rung 29" 4-Step Ladder: 38 5/8"
Height: 5' 7" 3rd Rung 28" 4-Step Ladder: 37 3/8"
Height: 5' 8" 3rd Rung: 27" 4-Step Ladder: 36"
Height: 5' 9" 3rd Rung 26" 4-Step Ladder: 34 5/8"
Height: 5' 10" 3rd Rung: 25" 4-Step Ladder: 33 3/8"
Height: 5' 11" 3rd Rung 24" The standard height of most ladders includes a rung at 24"
Using a tape measure, or a marked piece of tape, determine the height of the ladder. Hold the measure straight up-and-down and don't swing it out to the legs. The ladder must be completely opened up. Bring a level up to your measurement and mark the ladder legs. These marks should now be parallel with floor, and in line with each other.
Chop off the ladder legs at this line. For the moment, you are now in violation of OSHA regulations. Why? Because the way we use steps is by feel, not by sight. The rise must be consistent from one step to the next, or we will stumble and fall. Ancient castles would sometimes put in a trick step that was off by a bit so that an intruder would stumble and make lots of noise, alerting everyone of his presence.
Nevertheless, I have used an irregular-stepped ladder for many years with chopped-off legs and a step about 6" off the ground. Not long ago, someone borrowed it from me and stumbled, so I retired it.
Step 2: Mark the New Location of the Rungs
If you want to check my math, I used the ideal 3rd rung height and divided by 3 to get the rung spacing, then added the rung spacing to the 3rd rung height to get the overall height. For example, my ideal rung is 30", which means 10" between rungs. 30" + 10"= 40"
Step 3: Move the Rungs
Knock the legs away from the rungs, pull off the rungs, pull the nails. Notice that the ladder rungs are all different sizes to accommodate the narrowing of the ladder as it goes towards the top platform.
Next, dry-fit the rung at its new location. Make sure the rung is level, and use the rung as a template to mark the leg along the bottom and top.
Set your power saw at a depth of 1/8" and make multiple cuts, notching the woods. These are called, "kerfs." Chisel out the material left between your kerfs. This will leave a big notch for your rung. If you have ever cut out a depression into a door for a hinge, this will seem familiar. If you don't have power saw, you can use a chisel. Use a hammer to chisel the outline, then make a series of cuts with the hammer and chisel perpendicular to the grain. Then chip away the wood between your hammered notches. Here's a 4 minute video:
Simply screwing or nailing your rung to the ladder legs won't work. The twisting action of your foot on the rung converts a screw into an axle and the rung will spin... like it did for my tree house ladder when I was 10. My Dad taught me the axle analogy. Pretty cool, Dad.
Drill new holes for your rods and put them back in, as well as their spacers. Spacers go in first, then tighten the nut.
If the new notches are anywhere near your old notches, then putty up the old ones with Wood Filler, or Rock Hard Water Putty, or Bondo auto body putty. It will strengthen your new notch. (In hindsight, I wish I had done the putty after the project was assembled, or waited until everything was dried and sanded. I kept squashing it.)
I didn't mess with wimpy little finish nails to fasten my rungs even though that's what the factory used originally. I used 1 1/2" self-drilling finish screws to provide additional security without splitting the wood. No such screws at home? PRE-DRILL!
Set your new ladder on a level floor. If it rocks or teeters, use a level on the top platform and figure out which leg is too long and trim it a tad. Remember, you can always take off a little more if you didn't cut enough.
Step 4: Supplies and Materials
Power saw or wood saw
Self drilling wood screws, 1 1/2" about the diameter of a drywall screw or smaller
Wrench suitable for your ladder's nut size
Level, 3' or longer