Outside corners on dormers needs special flashing details to prevent water leaks. This article explains two foolproof methods for making sure that corners shed water and stay dry for the life of the roof.
Missing Kick-Out Flashing Kick-out flashing is critical where a roof edge meets a sidewall. Without it, roof runoff flows down the wall and possibly into the wall. This is worst when there is a door or a window below and water can seep behind the trim.
Missing Gutter Apron When water flows off the edge of your roof, some of it clings to the underside of the shingles and dribbles toward the fascia. If you have gutters but no gutter apron to stop the water, it will wick behind the gutter.