Insulation for a pole barn

[samdog1954]

I have a Shirk 30'x40'x12' pole barn, the roof was insulated when it was built. Getting ready to insulate the walls. I was planing on using 1 1/2" insulation board. My question is: Should I cut the board & insulate between the girts or just go over them?

Thanks,

Egg Harbor Township,NJ