By the way, I am not a professional on the field, I am just drawing some ideas for my future house. After reading the code for my country I found the minimum at the edge is 12cm (4.72 inches). But I don't think they enforce it, since I know a lot of houses that doesn't meet that min requirement. I'd still like to improve my current design anyway.
I found this method http://popularstairs.com/basic-stair-building/how-to-calculate-stairs/part2 for "balancing" the treads, but I couldn't figure out how to apply it on a U shaped stair, specially when mine doesn't have a space between the two sets of stairs (like this http://designedstairs.com/wp-content/gallery/stair-u-shape/100_6603.jpg, where the wall seems to be below the higher set of stairs, and not in the middle). I attached the plan file I am working on, but didn't get too far.
Does anyone has some reading material like that one but for U shaped stairs? Or how is this method for "balancing" treads is called in english (not my main lang btw)?, because I couldn't find much info about it on google.
stairs2.plan