{Stevie] penelope thinks you should unwind the DNA a bit - you can have them as shallow and broad as you like. That's why she was so disappointed that the odd couple selling the house they looked at had decided that no-one with feet larger than size three - and certainly no-one ever carrying a basket of laundry - was ever going to attempt to go upstairs.
As a committed fan of staircases (I was looking at stairporn.org yet again on my lunch break yesterday) and a pedant, I would be much happier if they were called "helical staircases", unless the radius does actually increase or decrease as one climbs.