Building a 2-story log spiral staircase can be quite an accomplishment. This style is unique and will enhance your home and increase it’s value. If you like working with wood, this instruction on building staircases will increase your knowledge of building.
My company, Trails End Log Homes, was contracted to design and build a 5,000 square-foot home on the side of Whohink Lake in Western Oregon. I suggested spiral stairs to connect the two stories with the basement. It is the only one that I know of that uses Lodge Pole Pine poles as pickets to hold up the ends of the stair treads. We used this method to build the stairs from wood we obtained directly from the woods.
My first concern was designing the stairs to fit the home and, of course, what will happen when the two story walls settled. I solved that problem with using walls from a company called Lodge Logs. They dry their walls to 15 percent moisture content to the center. The walls, which were 26” high at the top of the gables, settled only one-and-one-half inch. That was perfect because the center post shrank from drying end wise about that much.
1. Cutting the stair tread slabs. We used a 32″ dead Ponderosa Pine. It had been down for about two years and had bluing through it (this makes very nice looking treads). We used old Betsy (an old Still chain saw with a 36″ blade) to cut it into five-foot lengths and then slice it into four-inch-thick slabs. You can get two slabs from each piece that will give you four treads. For a standard set of stairs you would need 14 treads. I always plan for mistakes and cut an extra two. Sometimes they will simply crack when drying. They must be thoroughly dry to 11 percent moisture content or less before planing and sanding. That is why we cut them first and let them dry. Then we will use a hand power plain to get them approximately three-and-one-half inch thick and then sand them smooth..
2. Designing the stairs is the next step. We chose a left spiral going up with the first two treads on a straight run or on half log stair jacks. This was to allow us to end up where we wanted on the second floor and still start parallel to the entry. The rise of the steps is determined by dividing the total height by the estimated number of treads (the last tread actually being the landing above). That is nine foot and one inch equals 109 inches divided by 15 treads equals seven-and-one-quarter inch rise. After several drawings of stair plans, we decided on one. You should do several designs till it fits your circumstance. The one we built has a 10-foot diameter opening through the main floor. There are 28 steps all together with the steps going from the basement to the second floor.
The center post was 32” high, 32″ at the bottom and 18″ at the top. This center post also held up the ridge as well. It was fastened to the concrete floor with a knife bracket or simply an 8″ wide by 3/8″ thick steel plate embedded in the concrete footing in the basement.
3. Cutting the stair treads to working dimensions. Each step is pie shaped with the small end being six inches or more wide and the other end four foot and four inches away and 26″ wide or wider. At 12 inches out from the small end you need nine inches to the tread. A beam saw is used to cut an angle cut in the five-foot long slab, which is four-inches thick. You cut from approximately six inches over from one end to six inches over from the other side of the other end. This needs to be adjusted so you will have at least 26″ or more at the wide end. Then cut off the narrow end so it is six inches or wider with a four foot and four inch long tread. This pie shaped tread will have a flat front or toe side and leave the backside, the Natural side, (where the bark was). Each tread must extend under the tread above at least three inches, at the wide end, so you can tie them together with the four inch diameter Lodge Pole picket. The length of the tread is four-inches longer than it needs to be at the bottom of the stairs in the basement but almost right at the top step near the second floor. Each step must be trimmed as you install them to the right length. This is because the center pole is 32″ diameter at the bottom and by the second floor is approximately 20″ diameter.
4. Building the main floor opening for the stairs. We squared the hole in the main floor, floor system 10 foot by 10 foot, then put in 45 degree angle beams till we had as close to a 10-foot circle as possible then we bent 3/16″ thick plywood strips, floor system depth, around the circle three pieces thick. Make sure the last piece is the finish piece you want to show.
5. The pickets size and type. If you have a full-spiral-stair-system two stories high, that would be 28 steps with two lodge pole pine pickets per step but these pickets extend up to the second set of steps too. The pickets extend from six inches below the basement step to three foot above the second story step. The pickets are bolted to both steps with a three eights by ten inch lag screw and two the main floor system as well. They extend above the top step three foot to hold the hand rail so the total length should be 14 foot. The diameter at the small end should not be less than three inches. You will need 28 of them plus a couple extra for ends.
6. Installing the first step. Place a notch in the center post seven-and-one-quarter inches above the finished floor of the basement one-and-one-half inch into the log center post three-and-one-half inches high (that is seven-and-one-quarter inches to top of the notch from the finished floor). It would actually be eight inches in our case because they were going to use three-quarter inch hardwood flooring not yet put down. Also you must be sure to double check your riser height so that 15 steps will come out to finished height at the main floor and second floor.
The first step in the basement and the first one to the second floor must be aligned so that the pickets will attach to both going up through the floor system. In this case, the height from the basement to main floor and the height from main floor to second floor is the same. If your home is different, adjust the rise of the stairs to accommodate. Then slide the pie shaped step into the notch and bolt with a three-eights by 10-inch lag screw from underneath at a 30-degree angle. Be sure to counter sink the bolt head with the washer. Then attach the three-fourth-inch lodge pole pine pickets to the outside end of the step. Make a flat place where they hit the steps and the floor system before bolting. The third picket will then be the first picket for the next step and so forth. You can pick the style you like whether you extend the picket below the bottom step or not.
I let it hang down 6″ and used a old-fort style stockade end which is 45 degree cuts around the edges with a chop saw set at a 45% cut. It looks like you used an ax on the end.
7. Putting in the next step. This is where you must take some time checking yourself before notching the center post. The top of the notch must be seven-and-one-quarter inch above the step below and the step nose must be six inches back from the step below at the center post. At one foot out from the center post you must have nine inches back from the toe of the step below! This creates a pie shape step showing when looking down at the steps. The back side of the bottom step should run wild under the next step and should be far enough back so that the front of the step above laps over enough for the Lodge Pole picket to bolt to the step above and the back of the step below. The space between the pickets must be four inches or less so you will have three pickets bolting to the wide end of the pie steps.
Note: if you want a smaller diameter steps you can use a smaller diameter center post and narrower steps. But the step must be 36″ from center post to pickets for NBC code. That should be around an eight foot diameter circle.
8. Building the landings. After installing the 14 pie shaped steps, you will need to install a beam from the floor system over the the center post and bolt securely. This should be the right height so you can bring the finished flooring out to make the toe of the landing. In the main floor a second beam was also brought over to the post at one quarter of the circumference of the stairs. Check to make sure you have enough head room from the toe of the step in the basement to the floor joist above. That should be six-foot-eight inches as per UBC code. Also, the second floor landing must be built so as to have at least three-foot by three-foot area. Then finish the floor to it as your have planed. Again make sure you have proper head room.
9. Installing handrails. Now comes the really fun part. You make the handrail out of quarter inch by two-and-one-half inch strips of oak or wider. Using about 40 C clamps or small bar clamps, clamp the first piece to the inside of the four inch pickets 32″ above the toe of the steps. Make sure the end splice comes together tightly. Two 12-foot pieces should be enough for the first run. Then start the next layer with a short piece three or four-foot long and stagger the splices for each layer. You must have at least six layers or one-and-one-half inch thick handrail when completed. Use plenty of wood glue and slowly clamp each layer letting each one completely dry.
Before the last layer you need to install one-inch thick spacer pieces of the lodge pole pickets using a draw knife to make them about two inches in diameter. Place one every six pickets drilling a hole through the handrail and the spacer. Then counter sink the head of a number ten screw that will go through into the picket. You should flatten a place for the spacer on the picket so it will set against it nicely. Then glue the last layer and start sanding. Cut the ends of your handrail at the first and last picket right next to the spacer and you are ready to do a final sanding and put a finish on the stairs.
You now have one of the prettiest log spiral set of stairs ever made. I hope you enjoy them.