Original vintage architectural trade magazine ad for DAHLSTROM METALLIC DOOR COMPANY of Jamestown, NY.  The Unit Idea of Building Construction is to sub-divide a building into just so many units as there are rooms.  In the event of fire in one of the compartments, the other ninety-nine units are as separate building.  flames may destroy all the contents of the single unit in which they originate, but because of the isolation the flames will not travel to the other units.  Old 1912 construction industry advertisement.