New construction windows are designed with a nailing fin around its perimeter to  aid in installation in a new home or renovation when the wall framing and exterior sheeting of your home is still exposed. The nailing fin is used to attach the window to the exterior sheeting surface perimeter of the rough opening of the house. New Construction Windows are also used if the existing window frame is damaged and needs to be replaced, or if a home is getting a new exterior and the existing siding will be removed. The style of window will bond to the building exterior wall to create the best result and defense against air movement, moisture barriers and water seal the window to the building envelope system.