Building a set of stairs...?
Answers:
Seems like you really need about 22 feet for the run if you want 12" treads and about 7" rise. That would be about 22 steps.
If you do 10" treads, knock off 22" (rounded to 2 feet) then you'd need 20 feet for the run.
You're going to have to make a turn somewhere to get it to fit in the 13' space.
Doesn't seem like you can make a friendly set of straight stairs in the 13' run. But even if you do put in the steep stairs and the upper level is for occasional trips for storage, I'd do it, it's better than a ladder.
Other answers:
Not sure what you mean by "legal" here, but you can certainly build a set of stairs to a 13' level. Remember "rise and run" in calculating your stringers (run is the horizontal distance from the bottom of the steps ot the point where the steps end at the top). If you have too short of a run, your steps will be very steep. Your rise (the height of each step) should be between 7-8" for comfort climbing (this doesn't matter if it's just, say, a storage area; only if it will be climbed on a regular basis).
Not sure what you mean by "legal" here, but you can certainly build a set of stairs to a 13' level. Remember "rise and run" in calculating your stringers (run is the horizontal distance from the bottom of the steps ot the point where the steps end at the top). If you have too short of a run, your steps will be very steep. Your rise (the height of each step) should be between 7-8" for comfort climbing (this doesn't matter if it's just, say, a storage area; only if it will be climbed on a regular basis).
Boy you are asking for a lot in such a tight space. By "legal" I think you are talking about meeting the Int. Bldg. Code (IBC). For residential use, you can use 9" wide treads and 8" risers. 36" wide min. width stair. Also the IBC requires a landing every 12' vertically, so you should have an intermittent landing. Let's do the math: 13'=156"/8=19.5 risers, so you need 20 risers at (156"/20=) 7.8" each and add a 36" for a landing at the middle, this equals 36"+ (19 treads @ 9"= 171") 171"=207", this equals a 17'-3" run, not good news for you. Check further - if this is only for storage, you can use a steeper stair or 'ships ladder'.
Good Luck!
You have to check with your town's building department. Codes vary.