I am building a detached workshop with an 8' overhead door. The building is 22' wide and I intend to build a double 2"x12" with a piece of 1/2" plywood sandwiched in between for the header over this opening. Looking at the IRC 2006 building code header table R502.5, this is within the guidelines to meet local code. My question is this; although it is adequate to meet code, is it adequate to not sag over the years? I hate to spend the $$ on LVL, but don't want sagging 10 years from now.

Thanks in advance,

Kevin