I’m building a pole barn in snow country. The roof is to be metal on a 4/12pitch.The 2×8 purlins are 16″ o.c. and span just under 12′(one bay span is just under 14′). They are attached to rafter 2×8 girts spanning the 14′ shed roof width w/joist hangars. The roof will be sheeted w/ 7/16″ osb. My question is: In the span of 12-14′ on the purlins, is one row of blocking enough, or should there be two?

Thank you for your advice,I really appreciate it. wb