Alternating tread stairs are terrific for saving space; you only put one foot on a tread at a time, so why make it go full width? By only putting in half a tread you can go up at twice the slope without any more work, a comfortable 7 to 8 inch rise with each foot just like you do now. You just have to remember to start with the correct foot.

On the Tiny House Design Blog, Michael Janzen designs a beautiful alternating tread stair out of boxes, in the Japanese Tansu chest style, which creates a lot of storage. He writes "I’ve not seen many alternating steps being built for tiny houses – yet. " which surprised me, because we have shown many of them. But I have seen few as nice or clever as this one. Add a handrail and it is probably not quite as safe as a conventional stair until you get experienced with it, but a lot safer than a ships ladder to a loft at night.

That's why OSHA sees them as no substitute for a conventional stair but a suitable replacement for a fixed ladder in industrial uses. Building codes prohibit their uses for habitable spaces, but do allow them for storage lofts. And of course, building codes don't apply to tiny houses, which is one reason people build them. (See: Think about safety when you build tiny houses)

Lapeyre Stair

A few years ago we looked at alternating tread stairs in detail and noted that one company, Lapayre Stair, flat out refused to service residential users, and noted all the negatives about them:

It is not possible to turn around on our stair. Nor can two feet be placed on the same level at the same time. It is difficult for children and the elderly to use our stair. In addition, the handrails do not meet the baluster (vertical rail) requirements for residential stairs. Children could easily fall through the rails to the ground below.

Interestingly, when you follow the link in that old post, that scary info is all gone,replaced with:

Does the Lapeyre alternating tread stair meet code for residential use?

Local authorities often have differing code requirements for special staircases, so homeowners who are interested in an ATS for residential use should check their local code requirements before ordering. Lapeyre Stair's alternating tread stair is manufactured for industrial applications.

Lapeyre Stair

So they are a lot less doctrinaire then they used to be, or perhaps found better lawyers. They also provide tools so that you can design and order your own. They come in gorgeous stainless steel, painted steel or a very cool looking aluminum casting. Check it out at Lapeyre.

Levitate Architects

The nicest alternating tread stair I ever saw was the Bookcase Stair by London's Levitate Architects. But it was not the main circulation route. We have covered many others, shown in this older roundup or the newer roundup here.

In the end of his post, Michael Janzen asks: "Would you consider alternating steps in your tiny house?" I would respond that they are far better than the ship ladders we see in so many tiny houses. I am still not convinced that people should be sleeping in hot head-banger lofts in the first place, but if you are, and don't have room for a real stair, the alternating tread is the next best thing.

Please note that stairs have long been controversial in TreeHugger, and I often write about them with my tongue planted firmly in cheek as I cherry-pick the quotes here.

Alternating Tread Stair Saves Space, Looks Gorgeous

The alternate tread stair was designed to be a perfect union of functionality, structure and form. With regard to functionality, the stair is comfortable, safe to climb, and spatially efficient; the open sides of the stair provide ample and well-placed grip locations.

More in TreeHugger

Stair of the Week is an alternating tread storage stair

Alternating tread stairs usually use up a lot less space than conventional ones, and are safe and comfortable once you get used to the fact that you have to lift your feet in the right order. In previous discussions about them, owners have suggested that handrails are nice to have as it is a bit different than conventional stairs. I suspect the handrail police will complain.

Stair of the week combines desk, storage and alternating treads in one dramatic sculptural form

The handrail police will no doubt complain that this is the most dangerous stair shown yet on TreeHugger, being a combo of alternating treads, no handrail on either side, and totally covered in trip hazards. Picky picky. Look at how many functions it combines in such a small space and how interesting it looks, how it makes the stair totally disappear into furniture.

Czech Out Another Alternating Tread Bookcase Stair

Atelier SAD

It is by Adam Jirkal, Jerry Koza and Tomáš Kalhous in what looks like a renovation and addition in Všenory, Czech Republic. The stair appears to be made of slats of wood bolted together. Oh, to have building codes that let a thousand architectural flowers bloom.