• Building Construction Categories (ISO) are building construction categories established by the Insurance Services Administration, Inc. (ISO) in the Commercial Lines Manual (CLM) for the purpose of developing commercial property insurance rates based on exposure to fire damage. The six categories of ISOCLM building structures and the corresponding ISO building codes, from the category with the least fire resistance to the category with the highest fire resistance, are as follows. *Frame Exterior walls made of wood, brick veneer, stone veneer, iron-clad wood, or stucco on wood. (Building code 1) * Beam masonry is an exterior wall made of stone material (adobe, brick, concrete, gypsum blocks, hollow concrete blocks, stone, tiles or similar materials) with a combustible floor and roof. (Building Code 2) * Non-combustible exterior walls, floors, and supports made of metal, asbestos, plaster, or other non-combustible materials. (Building Code 3) * Non-combustible masonry Same as beam masonry, except that the floors and roof are made of metal or other non-combustible materials. (Building Code 4) * Modified Fire Rating - Exterior walls, floors, and roof made of masonry or refractory material with a fire rating of at least 1 hour but less than 2 hours. (Building Code 5) * Fire-resistant exterior walls, floors, and roof made of brickwork or refractory materials with a fire rating of at least 2 hours. (Building Code 6) The American Association of Insurance Services (AAIS) uses nearly identical building construction categories in its commercial property insurance rate development materials for several of its programs.