When you begin your design for a wood spiral staircase, you should first take into account the design elements of your home. You want a staircase that will match the current wood and decor in your home, not an obvious eyesore. Keeping this in mind, you then need to select the materials that you will use to construct your wood spiral stair and determine it's placement in your home. This article focuses on the design aspect of a wood spiral stair, actual installation is addressed in a separate article.
Define Your Space
The first thing you need to do is make sure you have enough space for the spiral staircase. A spiral stair is a space saving design, and only requires about half the space of a traditional staircase. But, there are several very specific building codes that you must follow in your design. The National Building Code requires that each tread (the platform you step on) must be at least 26 inches wide.
In general, your spiral stair will make one complete circle, factor in the center column and the handrail, and you have a total diameter of about 62 inches for the staircase. You can make the diameter larger to give yourself some extra room to make for a more comfortable climb, but 62 inches is the minimum. Try to build away from any walls to make the installation easier. If you need to build near a wall, give yourself several inches extra to make room for the handrail and have a margin of error. Make sure that the location of the stair works for both upstairs and downstairs and that no doors open onto the area.
Select your Design Materials
When choosing to build your own wood spiral stair, you have many options in terms of types of wood, finishes, accents, and colors. You can choose to buy a kit online, where they will take all of your measurements and calculate the exact size and height needed. If you aren't very skilled at math, this may be the route you want to go. These kits are also very customizable. You can choose different types of decorative balusters, decorative veneers for the center pole and many options for handrails. All kits are primed and you can choose your wood and then paint it any color you desire.
Of course, building without a kit also gives you all of these options. If you are going for a more modern look, you can choose metal balusters rather than wood. You can choose to leave the metal center pole exposed, or cover it with wood veneers that match your tread. It is even an option to build most of the spiral stair with metal, and then just add wood tread over the metal supports.
At this time you also need to choose whether you will have a free floating tread, or add risers in between the steps that close everything in. As soon as you have finalized your design elements, you need to get a building inspector to sign off on the project. Even if you are just buying a kit, you still need to have a building inspector's signature before they will even ship the kit to you.
Cut an Opening
Now that you have your permit, determined that you have the floor space to accommodate a spiral stair, and chose your materials, now you need to determine the amount of materials that you will need to purchase. You need to make a floor to floor measurement to know exactly how many treads you need and how far apart to make them. This is going to be where you commit to building the spiral stair.
To get this measurement you will have to cut the opening for the stairs. Remove any carpeting on the upper level, then make a chalk outline of the diameter of your staircase. Draw a square around this diameter. Add an additional two inches, both width and lengthwise. Use a circular saw to make the first cuts and then switch to a reciprocating saw when you get to the corners.
Before you cut the floor joists, support them with 2x4s for temporary support. Then reinforce the floor by adding double joists with 2x8s that run the length of the room. Secure them with a framing nailer and add joist hangers for extra protection. Now that you have the opening you can measure the floor to floor measurement.
Calculate Materials Needed
With the floor to floor measurement you can calculate how many steps your stairs will have. Keeping in mind the building code, each step needs to be 26 inches wide, you must have headroom of 6.5 feet at every turn of the stairs, and the handrail must be 34 to 36 inches above the nose of each tread. For the purposes of this article, lets assume that your floor to floor measurement is nine feet.
Since the ideal rise between steps is seven inches, we'll divide 108 inches (nine feet) by seven—that equals 15.43. Since we can't build half a step, we round down and go with 15 steps. Your landing will be your 15th step, so you just need to purchase 14 steps plus a landing. You will also need an average of three balusters per step, more if you are going to add a railing above the landing.
You will also need a center pole. Schedule 40 steel pipe works well as a center pole. It needs to be at least nine feet, higher if you want to use it as part of a railing system above the landing. Don't forget to include the spacers that go in between the treads, the newel posts, and also any decorative wood veneers to go over the spacers. Finally you will need to purchase a pre-formed handrail to complete your wood spiral stair. Now that you have your materials and design out of the way, you can start building.