Presume it was felted because 12 deg is not enough for tiles to function properly.
You might be able to find a special tile designed to function where the pitch is limited.
Worth noting that roofs are only felted / fibreglass / Rubber when tiles cannot be used as simply, they aren't as good.
As with all roofing finishes, they are all only as good as the quality of install. So the question is better phrased as what is the finish my carefully selected trade is most willing to use, and why?
Presume it was felted because 12 deg is not enough for tiles to function properly.
You might be able to find a special tile designed to function where the pitch is limited.
Worth noting that roofs are only felted / fibreglass / Rubber when tiles cannot be used as simply, they aren't as good.
As with all roofing finishes, they are all only as good as the quality of install. So the question is better phrased as what is the finish my carefully selected trade is most willing to use, and why?