Thank you for the quick response, Alex. Yes, the marked strings are against a wall, but they are the right side, as the stair moves up anti-clockwise. There is a window  (1200mm wide) in the middle of the wall on the right side of flight 2. This is why I thought it would be easier to put a handrail and bannisters on that side, then continued it on flight 3 for uniformity. It takes up space on the stair, but I don’t see an easy alternative.

I had not thought as far as penetration of risers, and the values used for penetration  were arbitrary. Thank you for the correct values. I have made corrections in the plan. I was planning on constructing the steps as the 3 flights separately, then fitting them together.

I did the design with curved strings and bannisters as an alternative, but seemed complicated and didn’t look like a comfortable walk. What would your opinion be? 

Thanks again.

Derek