Stair Technical Considerations - Rule Of Thumb

I've been working on a series of articles about designing stairs. There isn’t any special order to them. The first one was Commercial Stair Layouts Rule Of Thumb about a month ago.

The technical considerations I’m talking about are selection of materials, and structural detailing. Here is how I usually proceed. The vast majority of buildings we have designed are Type 2B, which back in the day was known as “unprotected non-combustible”. That ’non-combustible’ part all-but-eliminates wood stairs. But other issues that work against wood are the width of stair required in non-residential buildings and the difficulty of joining the members structurally. It may sound odd but it is much simpler to build a steel stair. The standard joining methods scale up very nicely in steel; not so much with wood. This leads to not only more difficulty designing the stair but also building it. The perceived savings by using wood quickly disappears.

We can dispatch concrete stairs by simply saying they work great, easy to design and, unfortunately, require lots of skilled carpentry labor to construct. This prices them out of reach for most budgets.

Steel is the workhorse when it comes to commercial stairs. You see them everywhere - confirmation of their fitness. You may have also noticed that they can be ugly.

The typical exit stair is made from channel stringers, a concrete-filled sheet metal pan resting on angles fastened to the stringers. The railings are steel pipes with steel bar pickets at 4" o.c. It can get rough. But there are several things you can do to improve the looks. These are simple and well worth the effort and cost if the stair isn’t completely utilitarian.

1. Add a drywall soffit to conceal the underside.
   
2. Use a plate or a rectangular tube instead of a channel for the stringers.
   
3. Frame the railings out of angles for rigidity and cover them with studs and drywall with a decorative cap and handrail. 
   

A couple of other tricks that improve the appearance of stairs are: 
a) adding a little width to make a more gracious appearance; 
b) holding the descending riser back one tread on a switchback stair so the handrail can make a smooth transition; 
c) splay the stringer(s) at the bottom for a spartan version of a Renaissance flowing stair; 
d) use the strength and workability of the steel stringers to ’suspend’ and display the stair.

Once you are conversant with the detailing and code limitations, push the limits.

If you are ever in Las Vegas, check out the stairs in the high-end shopping venues to see how you can make the stair into an art object! Sounds like tax-deductible research to me.


Stair Finishes are considered here.