Masonry noncombustible construction is 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.