Laminated Exterior Stair Stringer Details

      Some ideas for constructing exterior spiral stairs, with a wrinkle (stone treads and a stucco cladding).October 19, 2013

I have a customer that is asking us to quote plywood and glue to be used in a set of exterior stairs that will have a mild curve in the shape. Stairs will have direct exposure, but material will be wrapped and covered in stucco. They will be free standing with stone treads. My initial response is that I will be glad to quote exactly what the structural engineer specs. They want to present their customer with both a steel and a wood option. To help my learning curve, I would like to see if anyone has laminated a similar set and what their recommendations might be. I have already raised the obvious structural and durability issues.

Forum Responses
(Architectural Woodworking Forum)
From contributor J:
Marine grade fir plywood, resorcinol and deck screw fasteners. I pre-scarfed all the plywood joints and bent the whole wrapped bundle around a form (two-man job minimum). I also used a lot of shop-made clamps. I did not use any screws since the surface was exposed. The completed structure was epoxy sealed and marine coated. This bay-front stair never rusts and requires less maintenance than its iron counterpart.

From contributor L:
Stucco always cracks, so it will let water in and then keep the wood wet. Durable?

From the original questioner:
Thanks for your comments. You gave me the backup I needed. I have introduced my customer to WOODWEB and he thinks that it is a great resource. A structural engineer will make the final decisions. We just needed to be sure that everything was considered during the initial planning.

From contributor D:
I would suggest the use of an exterior grade wood and a non-creep exterior grade glue so laminations will not spring. Mortise and tenon fit with stainless fasteners and exterior adhesive to keep the stair together.

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