Commentary on Sections Part 3: Planning Control. Section 59: Matters which may be raised in an appeal under section 58
A party to the proceedings of an appeal under section 58 will not be able to raise any matter that was not in front of a council or the Department when it made its original decision.  The only exceptions will be if the party can demonstrate, to the satisfaction of the Planning Appeals Commission, that the matter could not have been raised before that time or that its not being raised was due to exceptional circumstances.