I need to replace my existing patio cover because the redwood 2x2 boards are warped and starting to deteriorate. I was considering replacing the boards with 2x2 composite, but my local lumber yard says they are not designed for horizontal placement, and that the boards will sag (they will have to span support beams that measure 4' on center). Can anyone confirm this? I really like the low-maintenance and durability of composite, and would like to use them if possible. Thanks.