Windows need to be flashed in a specific way to prevent water intrusion into the wall system. One of the most important types of window flashing is something called “head flashing”. This type of flashing is located at the top of the window trim. It starts out underneath the siding and then it’s wrapped over the top of the window trim. This is very important to prevent wind driven rain from running down behind the window. In this picture the window does not have head flashing and could leak.