Here is a great simple primer on roofing details that work and those that do not. As it is with many things, the KISS principle is usually best when we are talking roofing.
These are good pointers to know now, as we enter winter with it’s ice dams and curiously uphill flowing melt that lead to leaks.
If your home’s roof has these problematic roof details, understanding their issues means you can keep an eye on them and be prepared with good knowledge for when repairs are needed. They will be needed! Martin’s 10 Rules of Roof Design