Here is a spiral staircase we are designing for a client. We salvaged an antique round oak beam. It measures 14 feet long and is a solid 8 inches in diameter. The wood is so dense it takes four guys to lift it. We tried cutting it with a chainsaw and broke the chainsaw. It is really beautiful old growth wood.
We suggested we notch old joists into it to form a spiral staircase. The joists are 14 inch wide and 4 inch thick Douglass fir. We hope to salvage an old fire escape to do the railings.
Here is an image of the planned stairs. The rendering is by Architect Nick Liberis.