Stairs Part I: Stringers

Much like the exterior doors that I wrote about earlier, stairs say a lot about a home. You can’t just have plywood stairs in a log home – it’s distracting at best. And it looks cheap at worst. We wanted something that fit with the style of the home, but doesn’t take over. While looking at stairs I saw a lot of stairs that are the focal point of the home, and it just doesn’t seem practical for our home.

I set about learning all I could about stairs. I found out code is pretty strict on stairs – not nearly as strict as with chimney pipe, but still precise. You can’t have a nose on stair treads that rounds more than 0.5 inches; you can’t rise more than 12 feet without providing a landing; you can’t have a handrail greater than 2 inches in diameter; no riser can vary more than 3/8 inch height from any other riser in the staircase; and on and on. It’s exhausting to research. I guess the code people think falling down stairs – along with electrocuting yourself in the bathroom, or burning down your house with a wood stove are things they should be strict about regulating…

Manti Temple Spiral staircase

Entire trades are dedicated to building stairs, or at least they used to be. Two of my favorite staircases are found in the Manti Temple in Manti, Utah, built by pioneers in the 1800’s. The stairs in this temple rise four stories tall. When I went there, I always asked to look at them – they are a marvel to see. They are spiral sets of stairs, and not only that – they are elliptical spirals. In one tower, the stairs rise in a clockwise spiral. In the other tower, the stairs rise in a counter-clockwise spiral. This means that all the calculations had to be made separately for each set. The staircases are self-supporting, meaning each step supports the one above it. When the building was being renovated in the 1980’s, the stairs were over 100 years old. The inspectors and engineers removed a tread to inspect the stairs and found that the joints used to build the stairs had fused together so perfectly that they couldn’t determine one part from another. They closed them back up and left them alone. I’m only aware of a few sets of self-supporting staircases of this size in North America. The US Supreme court building houses another set of them.

I asked John Fetzer (when I worked at Fetzer’s), who is a great-grandson of the original architect for that temple how they built those stairs and he said nobody knows – the method has been lost.

Nowadays, it’s not much of a specialty anymore – you can even buy precut stringers at the hardware store. Treads are pretty common to buy as well.

My stairs will definitely be a poor imitation of anything in a glossy magazine. But the neat thing is that they will be completely “homemade”: meaning, the stringers are cut from a tree on my property that I milled, and the treads are from a dying oak tree a friend offered me.

Building with green (not kiln-dried) wood

Freshly cut wood has a lot of moisture in it. Normally, you buy wood from the hardware store that is dried in a kiln (a hot room) to get the moisture content down to an acceptable level. As it dries, it shrinks dimensionally. This is one reason why when you buy a 2×4, it’s not actually 2″ by 4″ – more like 1 – 3/4″ x 3 – 1/2″.

You can let your wood sit for months (or years) and it will eventually come to some kind of “equilibrium” of moisture content, but you’ll never reach “kiln dried” moisture percentages. One website I found said oak dries at a rate of 1 year per inch.

The problem with my stairs is that they will definitely shrink a little more once they are in place. Luckily, others have blazed a trail before me, even though a lot, but not all, of the knowledge of how to build with “green” wood has been lost. The Manti Temple stair builders of the 1870’s definitely did not have access to a modern kiln. Knowing how the wood will shrink, you can plan ahead with how you construct with it. There are various calculators online to figure how much shrinkage you can expect from a certain type of wood.

Making stringers

In a normal house, you buy 2×12’s for stringers, then use your right angle square to cut bird mouths out of it that match the rise and run of your stairs. I wanted something a bit more elegant and fitting for a log home. I started by pulling a log from this pile my neighbor made for me while clearing his driveway:

Originally, my plan was to mortise the stringers and tenon the oak steps, then “pin” the whole thing together. There are a few ways to do this. Here’s one way.

Stair model. Each inch = foot. Treads are tenoned through the stringers- not going to do it that way after all. Also we will have risers.

But the more I measured and figured, the more I realized doing a mortise and tenon style is really only worth it if the stairs are “free standing”. One of my stringers will be bolted to the log wall. This means half of my hard work would be inside a closet – forever unseen. I talked to a few carpenters and found out that even with 25 years of experience, and lots of help, a mortise and tenon stair case is still difficult. I’m one guy, with no help, and no experience building stairs. When you find yourself in a hole, the first thing to do is to stop digging. I discussed with my wife and decided to just do metal brackets to hold up the treads. Brackets will do just fine. No one will see them. And honestly, very few folks would recognize the craftsmanship of mortise and tenon joinery anyway.

It was very difficult to give up on this idea – I had my heart set on this type of stairs for a few years, but I was also losing sight of the goal: a strong house and hoping to move in this year (2022). Spending months on the stairs just isn’t pragmatic when I can get the same result with less work and less stress. But I look forward to doing this type of work when I get my garage / shop set up…

We had a hard time deciding which would be the best way to attach the stringers to the 2nd floor – for our design, the stringers end up attaching to the butt-end of the 2nd floor joists – which is a terrible place to attach stringers because drilling into the butt-end of a joist is a weak place to make an attachment point. With these heavy stairs, I didn’t want to chance the whole thing collapsing.

We came up with adding a 6×6 oak post to support the outside stringer. The joist is cut back 6″ to allow the post to be flush with the front edge of the 2nd floor. I cross braced the oak post under the house, and may eventually pour a concrete pad and add support for the stringer feet and this post. It’s all pretty heavy, and I don’t want to add more stress to the subfloor than I have to.

All of it was moved around with two pulleys while I worked on it – the 15′ oak post weighed around 300 lbs before I cut off the last 5′. The stringers weigh over 300 lbs each (the calculator says 328 – 497 lbs green (wet)).

With the extremely heavy oak stringers, and the 40″ wide x 1.5″ thick heavy treads – the whole staircase is going to be too heavy to move unless I just build it in place. So while I was looking for ideas on building the stairs, I was also looking for how to build the stairs in place. I ended up doing it by:

  1. Setting the back stringer against the wall, cutting the bottom angle and the top angle to get it to fit in the little cubby hole under the 2nd floor and above the girder log. I also notched out two wall logs near the bottom to get it to fit a little more flush up against the wall.
  2. Temporarily setting the 6×6 oak support post for the front stringer up against the floor joist, setting the front stringer up against the post and marking a cut for a channel in the post, then cutting the channel into the 6×6 post for supporting the stringer. This isn’t absolutely necessary – the bolts would probably hold the stringer just fine – but having a channel in the 6×6 post will give the stringer a strength you just won’t find in normal stairs.
  3. Cutting the channel into the 6×6 post and then permanently installing it.
  4. Installing the front stringer onto the 6×6 post.

Not sure I need to say this, but everything must be cut exactly the same on both stringers and all the treads, which is difficult when both stringers have live edges and don’t match each other exactly – there is no reference point to measure from. I used an online stair calculator for a bit, but found the estimates it was giving me were off by 1/4″. This is within acceptable limits, but I decided to draw the same thing myself in Librecad just to see where it was having rounding errors:

The more I calculated, the more confused I got – what should I use as a reference point? The stringers are not “2×12” material with straight edges all around, and they swell at the bottom while getting narrow at the top. The edges are not square. They bow just a bit. I kept measuring and thinking (I’ve never done stairs before), and then I realized – I’m working with a parallelogram – the top and bottom edges (the ones that touch the floor and the ceiling / bottom of the second floor) are parallel to each other. This means if I draw a line anywhere along these two edges that is perpendicular to the sides of the stringers, I end up with the hypotenuse of a Pythagorean triangle. And since a^2 + b^2 = c^2, with ‘a’ being the length across the floor, and ‘b’ being the height between the floor the top of the second floor, then ‘c’ will be the length of the red line (the hypotenuse) – the length of the stringer – where I needed to make my cut.

I measured the lengths on my libreCAD drawing to verify – and the calculations were off by 1/100th of an inch. I can live with that….

Finishing the stringers

Putting it all together

Lots of measuring and fitting before I make cuts. Pulleys are a lifesaver for moving these heavy pieces.

Next Steps

I’m already working on the stair treads, so look for a post on that soon!

3 thoughts on “Stairs Part I: Stringers

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