On Thursday, October 12, 2017 at 2:59:44 PM UTC-7, -MIKE- wrote:
https://photos.app.goo.gl/DqXrs5DI2roJTli22

I need to replace the white board above this garage door.
... I'm going to replace with a new, treated
2x12. (Client wants cheapest option.)

That's not a great plan; treated lumber (1) isn't straight, (2) isn't dry, (3)
doesn't take paint well. Could you put a bit of housewrap (or
even tarpaper) over it, as a kind of flashing, with a trim board overtop
that, and paint the trim? Hardieboard isn't expensive, and might come
prepainted.

Heck, even just cutting the treated board in the curve is going to be a tough job,
'cuz it'll be hard to see pencil marks.