How to Build a Spiral Staircase for a Cool Treehouse! 2026

How to Build a Spiral Staircase for a Cool Treehouse, a couple of important things to keep in mind about this guide:

• This is an advanced project, best suited for those with extensive carpentry experience.
• Due to the infinite variability of trees and treehouse design, this tutorial will not include a cut list for wood or a detailed materials/tools list.
• Dust off your geometry skills, because we're going to dive into a lot of math.
• I created the following charts as examples to help you move through the process; Naturally, your stairs will differ from my example based on your unique tree setting and treehouse design.
• Please note that improperly installed equipment can pose a significant risk not only to the tree, but to all parties involved.
• Following this guide is at your own risk.
• These plans are aesthetically inspired and will serve as the perfect starting point for your Treehouse project.

I hope you find this a useful resource for building your own treehouse ladder!

Step 1: Design and Process Considerations

The design process begins with defining the size of the stairs. Let's say you have an entry location on an existing platform in a tree.

The height of the stairs is the vertical distance from this entry point to the landing point on the ground. Determine how the stairs will fit around the tree. Imagine a “Virtual Cylinder” out of which stairs rise (see image below). In our "plan view", this cylinder completely encloses the tree.
I will refer to the radius of this cylinder as the "Minimum Radius."

Step 2: Placing stairs and making stringer patterns

With the minimum radius determined, we can design our stairs. This is most easily done on a flat surface. A scale plan of the staircase can be drawn on plywood as follows:

• Draw the minimum radius. We'll call this the radius of the inside of the treads.
• Draw inside the radius of the stringer. This radius is 6″ from the minimum radius to allow some distance from the frame.
• Draw the outer radius of the stringer. This is usually the inside radius of the stringer plus 36″ (standard stair width).
• Draw maximum radius. This is the outside extension of the stair treads, usually outside the radius of the stringer plus 3″.
• Draw lines of the stair tread. At 12″ beyond the inside stringer line (known as the “pitch line”), mark in 9″ increments (minimum stair tread depth). Draw stair tread lines through those 9” increments from the center point of the virtual cylinder. In this example, the treads form 10° arcs. It is also designed for four per string set.

Next, draw the outside stringer line at the points where the stair line intersects the outside radius of the stringer. Draw inside the line as the tangent to the radius of the inner spar and parallel to the line of the outer spar.

The stringers can simply be presented like this:

• Draw lines perpendicular to the stringer lines where the stringer lines intersect the stair tread lines. These represent the cuts in the stringer.
• Draw the stair tread lines parallel to the stringer lines, and misaligned from each other by the rise of the stair (in this case, 7″).
• Now youhas the cut design for your stringers. To finish cutting the ladder patterns, now design the knee bar cuts:

The bottom seat cut in the outside rail will be 3 1/2″ to fully support the knee bar. This cut is 11 3/4″ below the tread cut.
Measure 11 3/4″ on the inside pattern of the stringer to design the seat cutout. The upper seat cuts are 28″ higher.
The upper seat cut is aligned with the 5th vertical (perpendicular) line of the stringer line.

Step 3: Construction visualization

Build the stairs from top to bottom. This involves the use of temporary 2x4 scaffolding, a “1st Post” and a “Clock Ring.”

The scaffold provides reinforcing support before the knee pads are applied.
The post is used to refer to the height of the supports.
The clock ring is used to refer to the horizontal orientation of the knee pads. (Knee pads are installed after the stringers have been properly positioned in the space. This sequence ensures more precise placement of the stairs.)

The "1st Post" here is a vertical 2x4 with reference lines marking the top of the knee support heights. In the example here, you will notice that the scaffolding supporting the stringers is aligned with these reference marks.

The “Clock Ring” we use is a ring of 1/2″ plywood cut to the minimum radius and at least 8″ wide. I have shown the outer edge with straight cuts for simplicity. You can see that the lines on the clock ring refer to the orientation of the knee support.

Note that the center of the virtual cylinder is offset from C/L of the tree.

Step 4: Construction of stairs

The lines of the vertical and horizontal beams converge at the center of the knee brace beam. These beam lines refer to the 1st Post and a Clock Ring, both out of sight.
The patterns are made from 1/2″ plywood. They are used to orient the knee beams to the pallet flanges and to mark the through holes.
The lower support equipment is placed with beams. The patterns are used to fit the knee beam.
From here, you can continue this process to assemble the complete spiral staircase for your project!

Step 5: Admire your hard work!

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