When Idaho Power Co. relocated to its new corporate headquarters, it decided to upgrade and expand its former headquarters so it could be used as a computer operations and records storage facility. Plans for expanding the 1930s cast-in-place structure included constructing a precast addition that would match the original structure's 70-year-old Art Deco facade. Contractors Northwest Inc. (CNI), Boise, was chosen as the general contractor and also did the precast work. The project was challenging because the pre-cast panels needed to duplicate a variety of fluted columns, recessed shapes, and changing angles.
The original facade has eight depths, ranging from 7 ro 19 inches at the columns. Instead of constructing formwork for each panel, CNI built casting beds with four levels. A total of four casting beds were built, allowing for a two-panel cycle: While two panels were poured, two were curing. The lifting system for the panels required a concrete compressive strength of 3000 psi and a rupture strength of 500 psi. CNI used a 5000 psi mix with a compressive strength of 3800 psi and a rupture strength of 661 psi at 41 hours.
The greatest challenge was matching the ornamentation of the original facade. The new panels had to be exact replications. Rubbings of the old panels were made, then transferred to a sheet of 1/8-in hardboard, creating an exact jig for the new pieces to be nailed to. The fluted pattern was replicated by running one-inch-thick pine through a molding machine with a specially ground blade. The decorative panels were cast face down, and installed flush to the precast walls.