Can anyone tell me how to estimate the overage when siding a wall @ 45 degrees? I'm using shiplap planking to finish the walls of my basement. Instead of running the planks horizontally, I'm running them at a 45 degree angle, on a few of the walls. I've calculated out the cost of the materials if I ran all boards horizontally around the room. But I know there's a formula out there that will tell me how much extra to factor in if I'm running them at 45 degrees. I "thought" it was something like add an additional 10%, but I'm not sure. Does anyone know ? Thanks !