Alternating Tread Stairs




About: cheap guy, who likes DIY

This is a great option for people who dont have too much space in their offices or house for a regular long stair... you can save at least the half of the space without the problems of having smaller steps... its a little bit dificult to make the math, but is an excellent result, and you can make it as elegant as you can do it.
Let's get it on!

Step 1: Our Problem.

We have an office in an old building in Monterrey, Mexico, and we pay a rent of only $150 US at month, so is very cheap, but is not a big space... maybe 8m x 4m with two gigant windows in the front in one of the 8m sides, and the door is on the 4m side... so is a very small space but is very good ventilated and we are right in the downtown. So our first step was build a second floor with 3/4" plywood and a lot of wood beams and steel columns... so we need a strong stair but we can't use a lot of space. And my partner remember a desing that he saw back in his school days and in a lot of european magazzines: a Right foot stair.

Step 2: Our Solution.

So we start to think about it and make a few drawings and research... and we mix a lot of great ideas. We look for materials, and the best way to make it more comfortable and resistent.

We choose to use more plywood, two big wood beams and a little bit of steel.

We make the math for the hight of the steps and found the correct angle to have the 2.17m that we have to climb.

Step 3: The Angle

The plannig. Calculating the correct angle.

Down here in Mexico we make everything in centimeters so I gonna use centimeters and a aproximate in inches, in the end its the same.

We calculate 10 steps to climb 217 cms (85 3/4 in) and thats a little bit shorter than the average height in construction... but you gonna need to add steps and take a few fractions of inches in the case you have a higher floor.

We use a 3 parts to 4 parts scale to calculate the angle... this means that if we have 15 cm (6 in) of step and a 20 cm (7 7/8 in) height... the distance from the horizontal edge to the most higher point in vertical are 25 cms (9 14/16 in). You dont need to make hard (in my personal case I dont remember how to do it) mathematical operations to get this numbers... only draw it on a 100% scale on a big paper and its done.

So if you measure that angle... thats the one who gonna make all the work from now on.

Step 4: The Steps. Materials.

Once we have the correct angle for our stair... we can think about the steps.

First of all we need to desing the step shape. We decided to go with a 60 cm (24") long x 30cm (12") width. So its a very easy desing something like a "P" shape. (you will see it on the images).

All the secret of the space saving miracle of this kind of stair its on that "P" Shape and the position of it, you dont gonna put one next to other, you gonna put one OVER the other, and 'cause the widht is only of 6" in reality instead of the full 12" step you see on the regular stairs, so we are saving at least the half of the original long of the stair.

For make the steps we choose a 3/4" pine plywood... and making the calculate we know that we only gonna use a half of the board, but we were not too sure about the strenght, so we decided to glue two of them to make a bigger and stronger panel. You have to cut the board in half and then glue one half to the other to obtain a stronger 1 1/2" board.

Use any wood glue you know... and make sure that all the surface is on contact with the other. you can even put a few screws where you think may need it to keep it together.

Step 5: Cutting the Steps.

Once we have our big and strong plywood ready, we start to make a carton stencil of the shape to make sure that we have exactly the same shape in all of the steps.

Then we draw it over the board... but we make two stencils one for the right and one for the left... so we can alternate them and minimize the waste of material by puting one "inside" of the other.

We use a jig saw to make the cuts... dont forget to calibrate the angle of the blade and be patient 'cause some times the blade make a non desirable angled cut insted of a clean 90 degrees angle. Take it easy and practice... you can also draw the steps whit a 3/8" space between one and the next...this gonna be very usefull in case you need to rectify some cuts. (So dont be afraid to make a mistake...we can always find a solution)

Step 6: Finishing.

We have to use a lot this stair so we paint it with a high quality protective finish for wood something like the used on boats!

We want this stair on duty for ever!!!

Step 7: The Side Supports

In each side of the stair we gonna use two large and strong beams to attach the steps.... so we need to measure it and be sure that fits..

In this case we use a 10' beam and 2" thick.

We have to draw a scheme for this to make sure we are in the right direction.

First you need to se where you wanna put your stair... we use a very easy and secure way to attach this beams to the floor and to our second floor. (see the image). We use the first beam of the second floor to lay our stair... and we only put 4 guides to make it go straight, not for support part of the weight.

In the down part we put two strong steel parts to support the weight and this two parts goes attached to the floor by two big 1/2" screws. This is this enough to keep the stair in the floor.

Step 8: Attaching the Steps to the Sides.

We use a angle steel parts... (see the image) to attach the steps to the sides and support the weight when someone is using the stair.

We use two different sizes... 5" and 7 1/2" one for the 6" side and the other for the 12" side.

The 7 1/2" part has 3 (3/16") holes for screws in one side and 2 in the other. The other one, has just two holes in both sides.

this two simple parts are one of the most important parts of our proyect, 'cause they gonna support our weight.

Dont forget paint the angles... to avoid the rust.

Step 9: Support+steps

We have a 3/8" space from the edge of the back of the edge to the steel angle. Use wood screws to join the step and the steel angle.

Step 10: The Hard Part!!

Here's the hard part... mark in the side beams the hight of the steps.

remember the 37 degree angle? here we gonna use it...

Use something to mark the angle... and measure10" from mark to mark. (see the image).

Make sure you have the rigth angle... this is the key.



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    14 Discussions


    2 years ago

    Do you think the premise of these stairs could be build to be used as an unfolding attic stairway? I've got to get a safer way up to that area after falling off a ladder. And a standard pull down ladder isn't the way I want to go. I'd like to be able to descend from the attic forward facing and I don't really have the space to do much more than this anyway. Anyone ever build an attic pulldown stairway?

    1 reply

    Reply 2 years ago

    I´m pretty sure it may work... maybe you can take the mechanical parts of a regular pull down ladder and adapt this design... I think the problem will be about the space you need... the size may be as much as the double compared to a regular pull down ladder... so you have to make sure the hole in the roof must have the right space.
    Instead of having steps of 4 in a regular pull down ladder... you need at least 8 inches for this design to work safely.

    Hope you try it!


    Reply 7 years ago on Introduction

    I guess maybe... but you get use to really fast...
    we use it all the time... and even kids use it...

    humberto ribas

    7 years ago on Step 2

    This was made by the Brazilian inventor Santos Dumont, in the early 1900s.

    3 replies

    Frikin amazing!!!
    we saw this in old european magz but they didnt say anything about the inventor...



    I had one built for me, but these links are for the original one by him.



    7 years ago on Introduction

    I love it! I just built something like it. Look for "Single Step Stairs" but it is only four steps. Great job.

    1 reply

    8 years ago on Introduction

    Good work. FYI- They are called Alternating Tread Stairs.


    8 years ago on Introduction

    It´s a great solution... need some work... but its very effective!! good luck!


    8 years ago on Introduction

    these will work well in my new shop to save floor space :)