Frost appeared on the roof sheeting inside the non heated part of our basement. The frost is on either side of the venting with R-30 insulation. How can I keep this from forming? Should I put thinner insulation in so there is more space between the sheeting and the insulation?

The ceiling is vaulted and as of right now the insulation is not stapled in. The vents are not from side to side but in the middle of the rafter span. The temperature is 58-62 degrees in that area. The vents go out to the outside soffit.