When we roofed this home most of the ends of the composite siding on all the dormers were completely rotten and falling apart. The cause of this is because the siding was installed to close to the roof. This will cause the siding to hold water and will eventually rot/cause a leak.. etc..
Depending on how bad the siding is rotted we will either replace the siding and install it where it should be or you can actually cut out the ends giving the siding a space to breathe between the roof and the siding. This is one of the major causes for siding to go bad on dormers like these where the siding meets the roof.