Repost the drawing without the overlaid image from the architect. Hope this reads better.

This is the floor plan from the architect. There are at least 5 exterior walls from 2nd floor (over interior sections of the main floor footprint ) needing support beams.

1. The floor thickness (if that is what it is) has no relevance to the stair design.

2. Both suggested designs would feel awkward by making you lean forward as you climb which is especially difficult for children and the elderly.
The 7.5 riser should have a 10 tread
The 7.125 riser should have a 10.5 tread
A 1 inch nosing should be added to each tread but it is not part of the stair run calculation.

3. The winder as drawn is dangerous and a code violation. The narrow end usually must be a min of 5 inches so it rarely saves space but it can change where the stair starts and stops.

The landing should be the same width as the largest stair treads and the stair should not decrease in width as it decends because it is an egress path and also the primary access for furniture moving.

The clear dimension from the stair to the wall at the 1st floor should be larger than 38 inches. The double tread return seems excessive for the space.

Renovator,

Thank you for your response! This is very helpful.

1. Floor thickness.
I have no clue about the appropriate floor thickness (the space between first ceiling to 2nd ground). However, I do need certain ceiling height, say no less than 9ft. I understand that we do need to figure out the total floor to floor height (ceiling height plus floor thickness) as the total staircase rise. Right? Or do you mean that we shall go the other way around, let the whatever staircase total rise dedicate the ceiling and floor spacing arrangement?

2. Riser/Thread Sizes
We are expecting a baby soon and yes, we are not getting younger each passing day. So I am concerned about any potential safefy issues.

With the given footprint of 15' 4.5" by 7'6", I hope we have enough space for the required run and width to reach the desired floor to floor height of 142 (or 142.5 in my calculation) suggested by the architect. I am trying to use the smaller riser option (7 1/8" riser and 10.5" tread with 1" noser) to see if we can get it work. Let me know if you have any other options in mind.

3. Winder/Landing
I am not sure if my previous drawing was clear so I am attaching another picture. You can tell that the winder (thread #12 orange) is a trapzoid. The minimum width is 12inches, same as a standard tread depth. So clearly it was there not for saving any space but as a 'design' feature on purpose.

Is that acceptbable now? Or you sill suggest that the landing (tread #13 green) shall always be square or two squrares together at the U turn?

4. Clearance / Curved Threads
I have indicatd the 38" minimum clearance line on the first floor last step. It looks to me there maybe a problem with the door to coats.

The architect was trying to put the the curved stair steps as the focal point in the foyer. It may look nice but if there is any safey concern, we shall have just one step sticking out to the foyer/great room.

Again, the reduced tread depth shall let us have enough risers with reduced number of treads and that shall help the clearane issue.

This post was edited by jeff2013 on Sat, Jul 20, 13 at 22:01

I have no way of knowing how thick the floor should be.

The single winder is terribly dangerous and creates a strange handrail. If you want winders they should fill the space and be of equal size. Odd features don't belong in the middle of a stairway. if you are concerned about safety don't use winders of any kind.

The IRC requires that "the width of each landing shall be not less than the width of the stair served." That means the landing must be 4-1 instead of 3-4. It is also necessary to be able to move furniture.

The curved steps are fine but it is a big feature so it needs adequate space.

Location of the "winder" riser is a terrible design and safety hazard. Probably doesn't meet code either. It would be much better to simply make all the treads and risers identical. You apparently don't need a winder.

If it was me, I'd eliminate the curved stairs closest to the small hall closet and maintain maximum corridor clearance there. The curved stairs which die into the wall are fine if a "design" feature is desired.

Good luck with your project.

For a riser of 7.125 the treads could be as large as 10.75. The formula I use is T=20-(4R/3) which is recommended by the AIA graphic standards.

The riser numbering appears incorrect. Are you aware that the landing is just below the ceiling? You don't show the floor opening above so it is not clear how this works.

As for the floor thickness, that should have been settled before the stair had been drawn in plan. Ducts are usually in the basement or attic not in the first floor ceiling and when they are they fit between the joists or are shallow. If this is still being designed you should postpone the stair design.

This post was edited by Renovator8 on Sun, Jul 21, 13 at 8:00

Renovator and Virgilcarter,

We will get rid of the single winder in the middle and make both flights of equal width of 3-9. I am still looking at different riser/tread options from 7.5/10 to 7 1/8 / 10.75.

I am inclined to keep the curve stairs if there is adequate clearance. I am thinking of using a smaller closet door (from 30" to 24" door size) and/or steal some space from the HVAC clozet (from 42" to 36" depth) and shift the coat closet left.

BTW, I just received the first set of the elevations from the architec and I will post them separately. Please take a look and let me know what you think. Thanks! Jf