In the 2010 CBC and the 2011 Residential Code Sect R-806.2 the requirement has been lessened to 1/300 and the vapor barrier is not required if 50% of the venting is in the upper portion of the attic. (There is al alternative that if 50% of venting is not in the upper portion, that is acceptable with a vapor barrier).
I would like to understand the code change that lessened this requirement. We have a house built under the 2007 code which meets the later requirement, but not the 1/150 requirement. It appears, based on later codes, that it is adequately vented.