When you add the 2 by to the riser you lengthen the tread above, but shorten the one below and so on. No gain in tread width. To lengthen the treads you have to lengthen the overall length of the run. So if you have 12 treads and want them 2" wider, your stair has to become 24" longer. No way around it. Also to be a comfortable stair the risers should be from 6" to 8" and the treads 9-11". The sum of two risers and one tread should be between 24 and 25". I.e. for a common 7/11 stair, the sum of two risers and one tread is 25" (7+7+11=25). The risers and treads should be exactly the same step to step. If you are off more than about 3/16" you will notice in your stride up and down. You're right.
If my people, who are called by my name, will humble themselves and pray and seek my face and turn from their wicked ways, then will I hear from heaven and will forgive their sin and will heal their land. 2 Chronicles 7:14
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