I have, um, a ramp.
Okay, it's not entirely a ramp because it has a 39° slope of and you wouldn't be able to walk up it so someone nailed down some 2x4 cleats. But it's no staircase, either.
As you can probably guess from ye olde cedar shakes at the top of the ramp, this was a roof at one point in time. Parts of my house are 145 years old, so there are a lot of oddities like this caused by many renovations over the years.
The sheathing was a little suspect based on the several holes. Actually, I'm pretty sure it's not sheathing. It doesn't match the sheathing above, and it's varnished. Who would varnish the ramp to their attic?
I suspect that they pulled off the original rough cut skip sheathing under the shakes and laid down some scraps of used tongue-and-groove flooring. That change might have pre-dated plywood or just might have been Yankee ingenuity.
You can see the exterior wall on the left and the cleats are modern (probably 1960s) construction. The left wall probably had to be rebuilt when they tore down the barn that used to be attached to the building on that side.
The easiest solution would be to just lay plywood over the ramp and build a staircase with little plywood triangles holding up the treads. I did not do this. I, instead, opted for the most over-engineered and complicated solution to this problem, which was nearly my downfall.
I decided that there needed to be a landing at the top of the stairs at the same height as the attic floor. Aside from just being convenient, there's a column in the way so it would be a pain to get from the top step into the storage attic without a landing. Here's the nice completed landing:
This meant that the slope of the staircase (43°) no longer matched the slope of the ramp (39°). Here is where my troubles began...
I started with the landing at the top. I stripped off a few rows of cedar shakes, removed a few cleats, and laid down some 3/4 plywood underlayment.
Problem #1: I carefully calculated the angles to make this work out. What I neglected to take into account was that the ramp is not level left-to-right. In fact, it's off by nearly 3/4" over 3'! I had to re-cut the right horizontal landing support, but it all worked out in the end.
Now the bottom three steps are built on little triangles. That's because 39° is so close to 43° that there wasn't enough room to fit the depth of the stringer. Unfortunately they're not just triangles. There's a varying amount of rise on each triangle to account for the change in slope and the unlevel-ness of the ramp so each triangle is different! But so far so good.
Problem #2: After much head-scratching I eventually decided that my plan for making the stringer from that point was so difficult as to be nearly impossible due to a combination of angles and having to make up for the unlevelness.
Plan B added some more plywood and one more triangle support. This also eliminated the need to re-cut a stringer which would have caused me to run out of lumber prior to finishing the project.
Plan C added yet one more triangle-supported step (for a total of 5) and then a normal stringer and that worked. Whew!
And, 10 hours later, a completed staircase!
That included cleaning up, putting away all my tools, etc.. And a lot of running up and down the stairs since the attic is above the second floor and did all of the cutting outside at ground level.
There wasn't very much scrap left over. I live on a pretty quiet street, especially on weekends, and half the wood was gone in less than an hour!
Not bad for my first attempt to build stairs!
And as I was trying to calculate all of these crazy angles and distances I also wrote a Builder's Calculator web page that does addition, subtraction, multiplication, division and angle calculations in feet, inches, and 1/16th inch fractions.