Alternating tread stairs — the dream and the reality
February 22, 2008, 7:04 am by bottleman. Filed under: design, my tiny house project, tiny houses.

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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“because unfixed ladders aren’t regulated by the local codes. The disconnect between safety and permissibility was surreal!”

That is crazy.

And it by no means surprises me that a fat or obese person would have difficulty going up and down the stairs at all. There not active at all, that’s why there in the shape they are.

Anyways, nice looking stairs. Glad to hear you got them approved. It sucks to think that you might not be able to use the design you wanted in your own house without local government approval. But glad to see you got it in anyways.

I must admit though, I am real curious how you would get furniture to the second floor. Those stairs are okay, but it looks like the passage is not wide at all.

Comment by Adam on 23.02.2008 um 11:19 am

Hi Adam, thanks for the note. Regarding getting furniture up these stairs, it’s not that big an issue, since this stair goes to a small loft. There won’t be that much furniture up there, and if necessary, the loft has an open edge that could be used. You can see it in other pictures of the house on this site. Yeah, it would be more of a pain if the stairs went to a closed attic. Cheers!

Comment by bottleman on 23.02.2008 um 1:19 pm

Many people are willing to accept that they’ll need to move somewhere else if they acquire serious disabilities; and that’s in fact true for everybody in the extreme cases, like needing a respirator. Or plan to give up access to parts of their house if necessary (send other people to get things out of the loft, maybe).

The one that gets me is that any sort of leg injury requiring crutches or going up stairs on one leg makes these things unusable (or much more difficult and dangerous). Those injuries happen to lots and LOTS of people, often for relatively short timespans (so moving isn’t really a valid response).

This kind of stairs looks a lot nicer and would be a lot easier to use than ladders I’ve seen used to access loft spaces.

Comment by David Dyer-Bennet on 07.03.2008 um 3:10 pm

I have bookmarked your pictures of this home because I just love it!

About these stairs: I once had a cabin built for weekend getaway that came with a ladder to the loft. In no time at all I* built an alternating stair to replace the ladder. Get this, I am a fairly fat person and had absolutely no trouble with my stairs. The point is, once you get used to them, they are THE SAME (in rise and tread)as using a regular (minimum code) stairs. It is insulting to assume because a person is fat, they can’t manage these. Why would someone think that, along with extra weight comes uncoordination and befuddlement? Anymore than to think self-righteous prejudice comes with everyone named…Adam?

Comment by wyndwalkr on 02.03.2009 um 10:48 am

* Means I designed and built them with my actual chubby, middle aged, woman’s hands!

Comment by wyndwalkr on 02.03.2009 um 10:50 am

Thanks for the input, wyndwalkr. I agree, once you get used to them, they are the same as regular stairs, even for the less fit among us. And “getting used” to them means just two or three trips.

In general I find that the people who are most judgmental about these stairs have never used them. They remind me of priests and preachers, railing against the sins of the flesh. :)

Comment by bottleman on 02.03.2009 um 9:41 pm

Can anyone direct me to a “how-to” to build these things? I’m trying to build them on a deck to get to a roof line for a roof porch.


Comment by Josh on 26.04.2009 um 5:50 pm

Josh: if you look at the pictures carefully you can figure out several different methods of construction. The top picture has ladder style construction, but with treads that have cutouts. You can also build more standard-style stringers, with the run somewhat smaller than the rise, and put treads with cutouts on them. It’s possible to shape the stringers and cantilever the treads in such a fashion that each foot can have a very standard, comfortable rise and run. You’re going to have to puzzle it out on paper. This web page has a picture of someone constructing one:

In my opinion any design must have a strong, smooth continuous handrail that extends well beyond the top of the stairs — perhaps merging with a fence or something a the top. Good luck!

Comment by bottleman on 26.04.2009 um 8:27 pm

In your opinion, what is the best way to propose this type of stair to a jurisdiction and try to get it approved? I have seen multiple installations that are under the IRC that in reality do not comply with code, but somehow get through. Would you recommend submitting plans and seeing if it gets by and if the inspector questions it say that it was built per the approved plans. Or before you even do anything, write a letter to the director of planning and development asking to use this stair knowing full well it does not comply with code, etc. and trying to make a good case for it? It is really too bad that the IRC does not allow these in certain situations, like if they were to access one room that is under 150sq.ft or something like that. I can see them not requiring it for the main staircase in a two story home, but up to a single room loft or mezzanine. Thank you.

Comment by Charlie on 30.04.2009 um 1:24 pm

Wow Charlie, what a question. I have absolutely no idea what the best approach is. In my case the whole permitting process (of which the stairs were just one element) had been so absurdly screwed up that I ended up writing a letter to a city councilor. See this post: . But the basic argument is this: the #1 way to make a house more environmentally sensitive is to reduce its size. And smaller houses are going to require innovations like alternating tread stairs.

Not that presenting such a reasonable argument is going to work in many cases. The permitting bodies are set up to say no. They hew blindly to the letter of rules even when following those rules is absurd — see the “helpful” suggestion about the unfixed ladder, above. But perhaps the fact that I have gotten my set approved in the architecturally progressive city of Portland, Oregon, USA will be a useful precedent you can pull out.

I wanted to make my installation legal for several reasons, so I went through a lot of pain. But I know there are people out there who have just put something permissable (like one of those fantastic unfixed ladders!) on their plans and then pulled a switcheroo after the last inspection.

Keep me up to date. Maybe I can make your experience into another post on this site. Good luck!

Comment by bottleman on 30.04.2009 um 2:06 pm

I’m just about to start construction on a set of these alternating tread stairs and I’m curoius how the top portion is anchored to the loft floor. In the top picture the stringers continue on above the loft floor making it hard to see how it’s attached.

Any ideas out there? Is there a plum cut notch maybe?

Also, I found another set of alt tread stair plans here:

Comment by Matt on 20.10.2009 um 4:41 pm

I’m not sure how the ones in the top picture are attached. The only thing I know about those stairs is that picture.

In my own little house, the stair design is different. It uses regular zig-zag cut stringers on which the treads are mounted (some cantilever is involved to get the alternating tread effect). The type in the top picture looks easier to build and needs no cantilever (which seems like a good thing). I’m not enough of a carpenter to give advice, so I won’t weigh in on the precise design.

However, as a user of these things I definitely recommend that you make sure the handrail extends all the way past the top of the stair, and ideally extends continuously into the fence or gate on top (or whatever you have that keeps people from falling off). The handrail is essential for these stairs, and it is nice to be able to grab it easily even before you take the first step in the down direction.

Good luck! send pics!

Comment by bottleman on 20.10.2009 um 8:30 pm

Thanks Bottleman,

Good advice all around.


Comment by Matt on 21.10.2009 um 11:22 am

Hi there, we’re building a similar set of stairs up to our barn loft studio and were hoping you could send a few more photos of your stairs. We’ve spent all evening figuring out how to mathematically calculate risers and runners for this special situation, but it would help to have a few more photos. also, were all your stringers the same?

Thanks in advance.

Comment by Lindsey on 04.02.2010 um 11:01 pm

Lindsey, I don’t have more photos right now. My stairs were built on identical stringers but used a lot of cantilever on the active side of the tread. Now that I look at it, it seems needlessly complex.

Much simpler is the way they built the stairs in the very first photo in this post. Thick stringers with no zigzags, and treads between them, not on top of them. Obviously, you will need to assure yourself that the materials you are using are strong enough, especially, I think, the hardware that connects tread to stringer.

And like I’ve said before, pay special attention to the handrail. It should be continuous, and ideally merge with the fence railing at the upper level, so it can be firmly grasped before venturing on the stair.

Good luck, and please send pictures.

Comment by bottleman on 05.02.2010 um 2:51 pm


I’m working on a houseboat design on Sauvie Island. I would LOVE to use alt. tread stairs. Can you give any tips on working with the City of Portland for permit approval on this? How did you eventually get approval?


Comment by Kim on 23.02.2010 um 9:58 am

Kim, not sure I can offer you much advice on the permitting process, considering that the alternating tread stairs were just one part of a bigger bureaucratic mess: . I have even less clue about houseboats.

But there are basically two ways I have heard that people go about things like this: a) make your case, but be prepared for a fight; or b) try to sneak it through– for example, by drawing in a legit stair or ladder and then switching it for what you really want after the final inspection.

For various reasons I really wanted a legit building, so I fought the fight. But it’s hard for me to blame anyone who goes the other way. :)

Comment by bottleman on 23.02.2010 um 11:13 am

This is perfect for my loft. I now use the ladder and have fallen once already. These stairs are perfect and I don;t have to worry about codes.

Comment by karen on 27.07.2010 um 7:54 pm

Thanks for the data. Impressive work. Will be using this alternating stair design for access to sleeping loft in bunkhouse currently being built in my barn. We are almost there.

Comment by Kent on 04.01.2011 um 3:35 am

Permitting a spiral tread & not permitting an alternate tread for safety reasons is proof of bureaucratic ineptitude.

I built my alternate tread stairs in 1988 & they have been in daily use since. My office is just off the landing at the head of those stairs. For two decades my architectural photography equipment was stored at the head of those stairs & I moved 6 to 10 cases down & up for every gig. I never once had a misstep.That would have been quite literally impossible on a spiral & very marginal on a steep conventional stair.

I know that alternate tread stairs are safer & easier than spiral & steep conventional. I also understand that the new & outside of conventional wisdom appearance of alternate treads leads to a sort of intellectual ceiling for many including codes officials. The very first, competent study on the subject with supporting technical, scientific observations has yet, to my knowledge, to appear in the literature.

Comment by Bart on 04.06.2011 um 4:59 am

I recently started planning a small house (a “tiny cottage”) and was about to pull my hair out on the loft stairs. I don’t have to worry about codes but did want something with a small footprint that was comfortably navigable (no “standing ladders,” thanks) since this passage would be used daily and I am not a small person. While looking at spiral staircases and other options I ran across the alternating tread stairs (thank you Google!) and think they are a great solution. And Matt’s link to has a great example of alternating stair design (complete with measurements) that makes a great starter template for anyone interested in planning their own. Thank you, Bottleman, for posting about this. (And great-looking alt-stairs of your own there … they’re lovely.)

Comment by Dee on 13.10.2011 um 9:43 am

thanks Dee. If codes are not an issue for you, you might want to consider the Arke kit (reviewed here). While pricey, it’s pretty sturdy and adjustable so if you’re not into the carpentry challenge it might be suitable.

Comment by bottleman on 13.10.2011 um 12:36 pm

A ladder is not an acceptable primary access under the building code to any habitable “space” (such as a sleeping loft) — that is the case even if that space has less than the 7′ headroom required for a habitable “room”. A built-in bunk bed with a ladder is illegal under code. If it is instead a piece of unfixed furniture, then it is OK. As far as I know, Washington is the only state with the sense to permit ladders to small built-in lofts, even those with more than 7′ headroom — Washington does that by ammedning the national model code. The City of Oakland CA also does. Again, the code does not regulate furniture, but it does regulate built-ins. I do not agree with the code, but that is code…

Comment by Jim on 07.03.2012 um 10:51 am

I have these. They’re a single-stringer design, with the treads hung off the center stringer. They are great

One problem. When a cat sits on the tread, you have to boot it off, because you cannot step around it.

We put these in to replace a ladder leading to an attic, so we didn’t have to deal with codes. I understand that they’d be legal anyway, even if this attic room met the code as living space, because they are not the only way to access it. There’s a balcony with a standard staircase outside. This solution might work for those of you wanting to include alternating tread stairs in your house designs.

Comment by Grafton Kevan on 14.09.2013 um 9:11 pm

When I was younger and making off the grid houses using footprints less than or equal to the shed zoning laws in the PNW, we called the alternate tread design “marine stairs” and put an additional grab bar on the upper floor joist across from the stairs, such that you can grab it as you go down. The double railing is essentials as with practice , you’ll slid down on the rails, just like you see sailors do. Plan for it to happen. Due to a head and back injury, I cannot walk, but can take this style of stairs on my knees, effectively crawling. If you can crawl you can do this style of stairs. I’ve seen people with MS and CP, plus transected spinal cords use them via their bums. You just rock from side to side using the hand rails. I’ll see if I can find or make a video of this as it’s quite amazing. I can hoist my ultralight chair this way too (if they are constructed correctly).

Comment by Tami on 24.11.2013 um 2:04 pm

Great input, Tami, thanks.

I totally agree about the usefulness of an extra grab bar on the joist across from the stairs — it would add an extra piece of security for the downward trip. Of course not every installation is going to have such a joist (e.g. if the stair goes up to the edge of a loft instead of a full upper floor).

I would love to see videos of people using these stairs in unconventional ways. When people talk about “inaccessible” designs there never seems to be any recognition that people are not idiots — they can learn to use their bodies in different ways. :)

Comment by bottleman on 24.11.2013 um 4:32 pm

Thanks for your article, it was instrumental in getting me to go for this type of stairs. You give a good overview of the benefits and the points to pay attention to. I had to find a solution to get from my 2nd floor to a large attic where I’m building a room but unfortunately I have only limited horizontal space available and can’t do a spiral design. Luckily, no code issues where I am, as an owner you’re more or less free to do what you want, provided you won’t run a hotel or a B&B in the structure.

Comment by Werner on 22.01.2015 um 11:32 pm