Stair Layout Considerations
Stairs are another one of the features of a design that can take an inordinate amount of time. (Toilets are another.) The reason is invariably that the layout decided upon in Schematic Design doesn't work out on closer inspection in Construction Documents. Finding out that you need an extra 2’ leads to a bad day. Finding 2' means re-design.
I usually get myself in that predicament by not working out the concept of the stair in Schematic Design. I plan on a simple switchback stair, but it doesn’t fit; or it needs to be an ’offset’ switchback, which really doesn’t fit. (By ’offset’ switchback I mean you enter from a central corridor but exit through the exterior wall. Getting under the landing means one flight is extra long.) The point is that I wish I had spent a half hour thinking this through in SD instead of six hours getting it to work in CDs. So I like to run through all the possibilities in SD.
The simplest stair is a Straight Stair or its subtype Right Angle. A straight run works for up to a 12’ fl-fl then you need a landing. Obviously the entry and exit points are distant.
Switchback Stair - the old standby for a lot of reasons, inexpensive (or can be), stacked entrance/exit points. For a stair you don't expect to be used constantly, assume width is 10’ by 24’ long. For a stair you do expect to be used constantly, use a width of 12’ by 24’ long, which includes wall thicknesses in both cases. These dimensions are good for story heights up to 14’, which is ideal for buildings with ducted HVAC and 9’ ceilings. Both are good early assumptions.
Offset Switchback - If stair starts at a corridor but exits at an exterior wall it gets tricky because you have to walk under the landing. Set landing at 9’ min. A 3-story adds the problem that the ground floor stair has one longer run that has to be matched above for headroom.
Spiral Stair - they are expensive, trickier than most for headroom and for arriving at each level facing the correct direction. Code severely limits where they can be used.
Curved Stairs - they get complicated: code, comfort, technical issues, cost - consider going design/build.
Whichever type of stair is chosen, I like to keep the layout as simple as possible so I can concentrate on the aesthetics of the finishes rather than technical geometry issues.
Other posts deal with Stair Technical Considerations and Stair Finishes.