Installing a Spiral Staircase

If you decide to design and install spiral staircase in your own home, remember to think about the size and the shape of your stairway hole, your floor joists and hangers, plywood for your framing and about the right handrail and step treads for your spiral staircase.

The addition of a spiral staircase to a home provides the possibility of a slightly unusual means of accessing a bedroom, den or rooftop deck, while adding style to your home. Although they have been used for centuries, spiral staircases have never been common, mostly due to the difficulty of designing and manufacturing the staircase in a way that is both useable and attractive.

While it is possible to design and build your own spiral staircase, most modern spiral staircases are kits that are purchased and installed in homes. A kit provides everything you need, with all the engineering completed, to insure that you have an attractive, strong staircase, which meets your needs.

One of the most unusual spiral staircases ever built is in the Loretto Chapel, in Santa Fe, New Mexico. This wood spiral staircase was built by an unknown carpenter, who had passed through and saw the choir using a ladder to go up to the loft. He built the wood staircase, without nails over a period of several months. The truly amazing thing about this staircase is that it has no visible support members. There is no central column or side supports, yet it has stood as a testimony to that carpenter’s innovation and skill for over a century.

Before You Begin:

If you are planning on installing a spiral staircase in some part of your home, take a moment to consider how you are going to get any furnishings into that room. Spiral staircases are notorious for being difficult to negotiate while carrying things. Not only that, but the narrow space may actually make it hard to move most furniture via a spiral. It is recommended to have an alternate route for bringing in furniture, with the spiral providing a secondary access.

If you’re going to pierce the floor with your spiral staircase, you’ll need to determine the size and shape of your stairway hole in the upper floor, so that you can prepare for it while framing. Interruptions to your floor framing can be solved by using double floor joists around the hole; and joist hangers to insure that you have a good connection between the other joists and them.

For a round opening, essentially do the same thing; then block the corners at a 45 degree angle. Finally, apply a couple of final layers of thin plywood to the framing, to form the curve of the hole. Cut your plywood subflooring to fit.

Of course, a spiral staircase that attaches to the edge of a balcony does not require any special framing. It can attach directly to the header joist on the balcony.

How to Instlall it:

The key to installing a spiral staircase kit is the central column, as it supports the entire staircase. More than anything you need to be sure you have it located properly and that it is securely anchored to the lower floor. Anchoring to the upper floor won’t happen until the stair treads are installed.

The stair treads are built with brackets that slip over this central column, making for very strong construction. You’ll need to space the stairs around the central column and lock them in place, probably with a set screw. Depending upon whose spiral stair kit you use, the hand railing will probably be used to space the stairs, insuring an even rotation around the central column. Set everything in place, before tightening.

The tightening order for these kits is usually:

  • Central column base
  • Handrail to step treads
  • Step treads to central column
  • Central column top bracket

The top bracket is the last part of your spiral staircase kit to install. It needs to be very solid, so if you have put a round hole in the floor for the staircase, insure that you attach the bracket to one of the places where you have the double joists; that will give you the most rigid, wobble free mounting.

If you Decide to Design Your Own:

There’s a lot of math involved in designing your own spiral staircase. In addition to the rise of the stairs, you’ll need to calculate the angle. The easiest way to do this is to divide the number of steps you will have into the number of turns. In other words:

  • One and a half turns = 540 degrees (360 + 180)
  • Divided by the number of step treads – 13
  • Equals the angle for each step = 30 degrees

You must have the angle the same for each step, just like the rise of the step must be consistent; to avoid having a trip hazard.

The central column is your main support for the step treads, not the walls; although you can use them as an additional support if available; framing under each individual step. However, you won’t be able to frame under any open sides. To make the central column support the step treads, you’ll need to design and fabricate brackets that will go around the column and attach to the step tread.

The easiest way to build your own spiral staircase is to use a telephone pole as the central column. In this case, you can attach the step brackets to the telephone pole with lag screws, instead of manufacturing them with a sleeve to go over the pole.

Your steps will always be wedge shaped, with the narrow end at the central pole. Depending upon your stair design, you may have each step tread different (such as for a square staircase) or all of them equal. Be sure that your supports provide adequate support over both the width and depth of the step treads.

What You Need to Know About the Building Code:

One of the dimensions that you need to be aware of is the staircase diameter. Building code provides for a minimum 5 foot diameter spiral staircase. That isn’t very wide, especially when you consider that you have to take out for the center pole, and you’ll only have half of the diameter for each pie shaped stair tread.

The other dimension that you need to be aware of, if you decide to design your own spiral staircase is the step tread. This must be a minimum of 10” measured at the middle of the tread. Whatever angle you use for the rotation of your steps must allow for this minimum measurement.

If you buy a kit staircase, you will eliminate most of your building code worries. The engineers who designed that staircase have already insured that it meets code.

The kit probably won’t include the railing that you need to go around the stairwell at the upper floor. Don’t forget about that, or you’re going to have a great place for people to fall. You’ll need railing all the way around, except where there are walls or at the stair opening.

Tricks & Tips:

Think it through before you start. Make sure you have pre-determined where the staircase entrances are on both floors. Do they work out with traffic flows and furniture layouts? It’s easy to decide to install a spiral, without having taken into considerations how well it will fit. This can cause long-term problems with stairway access.

Money Savers:

Buying a spiral staircase kit is fairly expensive, so you can probably save money by building your own. Before deciding though, design your brackets and take the design to a welding or machine shop for them to price. You might be surprised how much they charge.

If you really want to save money, don’t bother putting in a spiral staircase. No question about it, this is a much more expensive option than building a standard staircase. However, if space is an issue, there’s nothing that takes up less floor space than a spiral.


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