We are building currently and have an area exactly as you describe in an AE zone leading to the elevator that is conditioned. Approx 36" is in the flood zone (14' above sea level), all area below this is required to be of pressure treated wood. Had to use thick rigid foam for insulation up to that area, or you can spray use closed cell spray foam, in the walls as well as behind the stairs. To be honest I haven't considered the finish on the steps but I believe we were going with carpet, guess that will change. In the North Carolina code it is in section R322.

Here is a copy from the international code:
R322.1.8 Flood-resistant materials.
Building materials used below the elevation required in Section R322.2 (flood hazard areas including A Zones) or R322.3 (coastal high-hazard areas including V Zones) shall comply with the following:
1. All wood, including floor sheathing, shall be pressure-preservative-treated in accordance with AWPA U1 for the species, product, preservative and end use or be the decay-resistant heartwood of redwood, black locust or cedars. Preservatives shall be listed in Section 4 of AWPA U1.
2. Materials and installation methods used for flooring and interior and exterior walls and wall coverings shall conform to the provisions of FEMA/FIA-TB-2.

Scott

This post was edited by incus on Sat, Apr 12, 14 at 8:56

Thank you so much for the info. Friends of ours tiled the pressure treated wood on their stairs so I think that's our plan for now. Was not expecting the added expense.