One of six building construction categories established by Insurance Services
Office, Inc. (ISO), in its Commercial Lines Manual (CLM) for purposes
of developing rates for insuring commercial property, based on susceptibility
to damage by fire. The CLM description of masonry noncombustible
construction, followed by the associated ISO construction code, is exterior
walls of masonry material (adobe, brick, concrete, gypsum block, hollow
concrete block, stone, tile, or similar materials) with floors and roof of
metal or other noncombustible materials (Construction Code 4). The construction
code indicates the ranking of this building construction category within the
six categories, with 1 as the least fire-resistive and 6 as the most
fire-resistive.