Fire protection system and methods for concealed spaces providing for effective fire protection over an effective depth range measuring from a minimum six inches up to a maximum that is greater than thirty-six inches. A combustible concealed space that includes an upper deck and a ceiling deck spaced about a longitudinal axis extending substantially parallel to the ceiling deck with a fire protection system having a firefighting fluid supply pipe and at least one automatic upright sprinkler coupled to the fluid supply pipe and positioned to define an effective depth range that measures from six inches to a maximum of at least sixty inches.