Summary: back side of most gutters is also vertical But without gutters much of the water coming off the roof runs down the fascia where it can rot the wood over time especially at the joints But a far bigger problem is the angle of the fascia to the sloped roof It varies with the slope of course but standard drip edge comes with just one angle which is 90 degrees Of course the
Image Dimensions: 356 x 253
Image originally found here.