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alternating tread stairs

SmokingWater's picture

I need to design an alternating tread stair and know nothing about them other than they exist.  Any help would be appreciated

(post #55242, reply #1 of 29)

Never heard of it, "alternating" between what, and what?


Brinkmann for president in '04

(post #55242, reply #2 of 29)

Assume you're referring to a so-called "ergonomic stair," with staggered treads. The theory is that, since you only step on any tread with one foot, you only need every other tread in succession, zig-zag-style, which allows construction of a steeper stair in a tight space. I persuaded a space-challenged client to let me build one, but proceeded on a seat-of-the-pants design basis. The stair was fun to make, looked cool, but felt pretty strange in use. First, a standard, average 8-inch rise I used is too low for such a steep stair. Ladder-type spacing, something around 12+ inches would feel more comfortable. My tendency was to overstep in climbing. I had to look down to place my feet - not intuitive. Also, though I've never paid attention, it's possible that one tackles a stair with a common leading foot, say, always right, or always left. I dunno, but this would require each user to adapt to the stair, which would force a default starter tread by design. Again, not intuitive. I guess my client adjusted to his stair - said he liked it - but I bet he got lots of unfavorable comments from guest users. Be a good idea to mock something up first and see how it goes over. Try temp treads on a rough three-stringer setup, alternating sides from the center stringer, and see what you think.

(post #55242, reply #3 of 29)

Thanks.  We're building a loft w/ limited space.  12 inches is perfect.  For future reference I did a quick study at work and found almost everybody starts up stairs with their left foot but up a ladder with their right.  It's unscientific but that's all I've got.

(post #55242, reply #4 of 29)

Interesting.Basically a ladder,right?How are the alternating treads an advantage over a ladder? I would like to see a photo when you get yours built.


what the heck
was I thinking?

what the heck
was I thinking?

(post #55242, reply #5 of 29)

>> How are the alternating treads an advantage over a ladder?

The treads are deep enough, front to back, to step on comfortably and safely. The corresponding disadvantage is that you can't stand with both feet on the same level.

(post #55242, reply #14 of 29)

How are the alternating treads an advantage over a ladder?

First of all, the Jeffersonian staircase allows you to descend with your back to the stairs, instead of facing them, as you would on a ladder.  This makes carrying items much easier.

Also, using a  deep tread instead of a rung results in less concentration of stress on your foot, so it is more comfortable.  Furthermore, the alternating tread makes ascension/decension easier because you don't bang your foot into the tread you would otherwise be trying to skip over.

I built a Jeffersonian staircas for a client a number of years ago.  They had two children who were about 9 and 11 at the time.  Part of the challenge was to construct the stairs so that they were comfortable for both the children and the adults.

I mocked up the staircase using common framing lumber and just screwed the treads in place for the mock-up.  Then, the kids and adults were both able to try it out.  With just one iteration, we reached a good design with which everyone was comfortable.

I don't know if it's to code, but we ended up using an acension angle of 66 degrees, with a unit rise of about 9-7/16" -- meaning the difference in elevation between the tread on the left and the tread on the right.  The vertical distance between treads on the same side of the stairs was twice that --- about 18-7/8". 

They've been quite happy with it, and have had no mishaps.  However, any newcomer to the house eyes it warily, and has a bit of difficulty getting the feel of it at first.

(post #55242, reply #6 of 29)

I'm copying a previous post from AndyLee about the alternating tread stair.  If you search loft ladders, there are several threads.

Wait, I thought it was Thomas Jefferson who invented the alternating tread sez so on the tour brochure at Monticello, but then, maybe he got the idea from Ben Franklin, who knows. Anyway, it is addressed in the BOCA code, 1996 commentary, section 1014.6.6 and described in Figure 1014.6.6. Alternating tread staircases are permitted for access to a mezzanine or loft area not more than 250 square feet and which serves not more than 5 occupants. Ladders, or "ship's ladders" to habitable space are not allowed, at all, except for folding staircases to attics which are closed off from the habitable space. Handrails are required on the alternating treat staircases, with balusters 4-inch o.c., with a guardrail and balusters at the loft platform. Tread depth is 8-1/2" minimum, and riser height is 9-1/2" maximum. Tread width is 7-inch minimum. Each tread has to project 5-inch from the one above it. I'm getting ready to build my second one to access a child sleeping loft in my tiny house model. They can be works of art, I made my first one from  5/4 clear eastern white pine stringers and clear western red cedar treads, with the newels and handrails 2-inch clear Douglas fir and the balusters 5/4 red cedar. Handrails are required on both sides. It is possible to build a alternating tread staircase only 18-inches wide overall, and requiring only 5 lineal feet of floor space, plus a 2-foot landing at the bottom, about what you would have in a bedroom closet. Compare that to a standard staircase that requires 3-feet by 12-feet space. The smaller staircase doesn't actually save you much space in a McMansion, but its a necessity in some of the little bitty houses I build. Regards, Andy Lee

The important point is that with alternating treads you can fulfill the requirements of the building codes in less space. 

Hope this helps.

(post #55242, reply #7 of 29)

Here is a photo of one we built, it's a tight little thing that goes up to a crows nest.

(post #55242, reply #8 of 29)

Beautiful work!

(post #55242, reply #9 of 29)

Before architects got hold of them, they were relegated to tight spaces where a typical ship ladder would not fit on a ship or in a factory, but a ladder was not practical because of the items carried by the user.

...that's not a mistake, it's rustic

...that's not a mistake, it's rustic

(post #55242, reply #10 of 29)

So are these steps something you could climb with your hands full,or would you need at least one hand on a rail? What are they like to go down? I've only seen pictures, including the nice one posted earlier...I would love to play on a real set.I may have a situation where I could use a set of steps like this; I am remodeling a house that has a small loft. Right now, the access is from a peeled pole ladder. We will be providing access to a new addition right where the ladder now leans, and I need to come up with a creative idea for getting to the loft later without using up too much space.

I have built extremely steep sets of stairs at times to access basements,attics, etc. but they were always full treaded.


what the heck
was I thinking?

what the heck
was I thinking?

(post #55242, reply #11 of 29)

Sweet, Armin.  I've never seen or heard of those before.  I wonder why they are safer than if the treads went all the way across though?


Brinkmann for president in '04

(post #55242, reply #15 of 29)

.  I wonder why they are safer than if the treads went all the way across though?

Jim, I asked myself the same thing when the customer asked me to build one. However once I started working on it the light came on. Picture this, the stairs are steep so if the treads were ten inches wide your toe would hit the underside of the next tread up, coming down is even worse since it would be like walkig down a step ladder forwards. The action of walking up stairs is to have one foot on a tread then lift the other foot up to the next tread. The missing section of tread allows your foot to clear the tread your standing on. If you were to walk up one blindfolded you would think you are climbing a normal staircase. Whats funny is to watch a dog or cat use one.

(post #55242, reply #16 of 29)

After initial apprehension, users tend to be very comfortable using these stairs.

...that's not a mistake, it's rustic

...that's not a mistake, it's rustic

(post #55242, reply #17 of 29)

We blew it on our stairs.  Good thing it's only for us.  We put our risers only 12" apart.  Every time I go up I have to double my step to make it comfortable.  Next time we'll use 18"

For the construction we used 2 x 6 treads between 2 x 4 stringers.  It isn't anything for show since it's in our office garage.  It leads to our storage loft where we intend to put old drawings and old files.  Again nothing fancy but very functional.

(post #55242, reply #18 of 29)

Well I can tell you why they wouldn't fly around here. Would you let your grandchild go up or down those things? Thus the reason for the 4" ballaster codes not to mention falling thru the steps.


"Rather be a hammer than a nail"

"Rather be a hammer than a nail" Bob

(post #55242, reply #19 of 29)

Hey Pro-Dek,

You're from the Puget Sound area, right?

Those clients of mine who had me install a Jeffersonian staircase got the idea from a new construction on Whidbey Island.

Maybe things aren't as bad out there as in King County.....



(post #55242, reply #20 of 29)

I think Whidbey Island lost it's mooring lines and is floating somewhere up near the San Juans, Ragnar, where staircase codes are real lax..........


"Rather be a hammer than a nail"

"Rather be a hammer than a nail" Bob

(post #55242, reply #21 of 29)

I wish we could import some lax building codes in our area!

(post #55242, reply #22 of 29)

Really! - Hows that bumper sticker go? "Getting welfare should be as hard to get as a building permit" :-)


"Rather be a hammer than a nail"

"Rather be a hammer than a nail" Bob

(post #55242, reply #23 of 29)

That's a great bumper sticker, Bob!!! I haven't seen it before.  One of my favorites is: "Don't steal -- the government hates competition."



(post #55242, reply #24 of 29)

Pro-dek, Look in the code book they are code legal in most places. Why I don't know, seems the only restriction is it cannot service a sleeping area or an area greater than 250 sq. ft. As far as kids go, they love them.

(post #55242, reply #25 of 29)


I've built a few of these and the advantage is that you can see the tread as you decend. With a standard tread, you can't see the tread because of the steepness of the pitch of the stairs. One thing though, you can't stop and turn around and go the the other direction until you reach the other end. It really is a freaky feeling the first time you use one of these because it seems like your not getting anywhere. Your brain isn't used to this type of pattern because it's not a ladder or a stairway it is kind of a hybrid.

Kevin P. Doyle

(post #55242, reply #26 of 29)

Well, I'm intrigued by the idea and I'm looking forward to giving them a try.  Plus, I'll admit I've been thinking about how cool they could look (but don't tell cloud hidden I admitted that, okay?).

Hey Ragner!  Where are you at? You in the Great Northwest?

(post #55242, reply #27 of 29)

Ya sure, ya betcha.  Here in Ballard.  ;)

(post #55242, reply #28 of 29)

There is a minimal run (5") from left to right. A full tread stair with a 5" run is a scary thought [unless you have really small feet :)] Alternating treads, however, will give you a 10" run on each tread (left or right)

(post #55242, reply #12 of 29)

Hi, I'm very interested in what you're doing for a loft. I live in a small condo with ceilings that go up to 16 feet and I'm thinking of adding a loft or two(including an alternating tread set of stairs). I'm hoping to add one loft over my kitchen and bath, but I'm hoping to keep the demolition of the existing studwalls to a minimum.

I considered doing a 4-6 post timberframe style loft, but maybe standard platform framing would be better. I'm thinking about 16' wide by 12' deep.

I'm having a hard time finding references to loft construction, since it's a strickly interior structure.

What style are you doing and what's the size or yours?

(post #55242, reply #13 of 29)

lapeyre stair commercialised the alternating tread .. they used to make wooden ones too.. i've got an old catalogue from the '70's..

now they do steel & alum... but the design is still the same

here's a link :!OpenDocument

Mike Smith   Rhode Island : Design / Build / Repair / Restore

Mike Smith   Rhode Island : Design / Build / Repair / Restore

(post #55242, reply #29 of 29)

unless the house you're designing doesn't have a stream running through the middle of the floor, a glass curtain wall anywhere, or tree growing through the floor in the living  room that the house was built around for environmental reasons, don't put those stairs  in.

just this carpenters opinion.