Alternating tread stairs — the dream and the reality


Here come the objections: Unpermittable. Uninsurable. Illegal. Or my favorite: impossible!

alternating tread ladder image borrowed from

[Ladder image borrowed from via materialicious.]

People striving to make environmentally sensitive housing often struggle against building codes and planning officials that tell them their environmentally positive design feature simply “can’t be done.” In the case of small houses or accessory dwelling units– which can be greener than a solar mcmansion just by being reasonably sized — one of the biggest challenges can come with stairways, since code stairways take up so much floor area and volume.

There are alternatives, of course, and here I’ll tell you about the one we used in my tiny house project: “alternating tread stairs” (also known as “monk’s stairs” or an “alternating tread device”). They allow comfortable ascents and descents in a considerably steeper pitch than a standard stair. They are usually straight, making transporting long items (like mattresses) easier than on a small-diameter spiral stair. (Though it is possible to curve them, as with the Arke Karina stair kit.)

They seemed like a godsend when I first learned about them, and I still think they’re awesome, but there are a few practical limitations I’ve uncovered in using them and watching people use them. I can talk openly about the pros and cons of this feature because (after many appeals) the stairs in my tiny house were approved and permitted by my city. They work well, but they are not a panacea.

An alternating tread design works by defining individual left and right treads for the left and right feet; if you have a different number of feet this won’t help. 🙂 Each tread has a cutout allowing the foot that is not supporting weight to swing through more comfortably. The ladder/staircase pictured above shows how much space the arrangement can save, but it doesn’t give you an idea of how easy going up or down can be, because the reach and rise of each step can be exactly the same as on a standard stair. If you don’t believe this, check out this intriguing demonstration done in Lego, by wikipedia contributor Diomidis_Spinellis. The alternating tread arrangement is in the middle.

alternating tread pic in the public domain -- source: wikipedia

The stairs in my tiny place look like this:

climbing up alternating tread stairs into loft

They’re steep, yeah, but the standard-sized rise and run make them easy enough to use for my mother in law, who’s in her 60’s. She won’t be able to use them forever — which is a critique some people make of such stairs — but then again she might not be able to use a standard stairway forever either. (The premise that every design feature has to be usable by every person for every moment of their life is loony… just think of where that would lead.) Meanwhile, the spacial economy of these stairs made a lovely & functional small home more possible.

There are a few caveats, though. Falls on this steep pitch could be serious, so the handrail is important. Using the handrail means you will only have one hand to carry things. And since people aren’t used to these stairs, they require PRACTICE. It might take just two or three uses to get that practice, but practice is essential. Several times I have observed a physically unfit and uncoordinated person taking their first trip down these stairs (you come down forwards just like on a regular stair), misjudging the second or third step, then stumbling a bit. They catch themselves with a hand on the handrail and then get down fine. After two or three uses they have no problem anymore. A physically coordinated person often has no stumbles at all.

So: you absolutely must have a decent and continuous handrail (or two). And you really shouldn’t place alternating tread stairs in a public facility, in my opinion, because there will be so many first time users. (At least until the day when everybody knows about them.) But otherwise, I think they’re a very practical option for small or efficient spaces. Certainly safer and more practical than the “solution” one plans examiner suggested (during the initial rejection of my alternating tread stairs)… “an unfixed ladder.” This would be permissible, according to the examiner, because unfixed ladders aren’t regulated by the local codes. The disconnect between safety and permissibility was surreal!

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