Look on the outside of the building wherever two different materials meet. Look at beam pockets, soffits, places where pipes, electrical conduits or other penetrants pass through the wall, and the areas where the roof meets the wall. Look at windows and doors. Look at electrical boxes and control panels. Keep in mind that visual inspection is unlikely to find all leaks. To most effectively air seal a building, consider an energy audit that includes a blower door test that depressurizes the interior space.