Construction types
Modified Fire Resistive
(ISO Class 5, IBC Type
IB)
Modified Fire Resistive
construction is ISO
Class 5. ISO Class 5
encompasses IBC Type IB.
Modified
Fire Resistive Buildings
are buildings where the
exterior bearing walls
and load-bearing
portions of exterior
walls must be of
noncombustible materials
or of masonry, but
exterior nonbearing
walls and wall panels
may be slow-burning,
combustible, or with no
fire- resistance rating.
Buildings with exterior
walls, floors, and roofs
of masonry materials
described in the
definition of fire
resistive (Construction
Class 6) — less thick
than required for
fire-resistive
structures but not less
than four inches thick,
or
Fire-resistive materials
with a fire-resistance
rating less than two
hours but not less than
one hour
Structural Steel
Protection
Modified
fire-resistive buildings
also include structural
steel protection
techniques —
fire-protection material
applied to steel.
Materials include:
concrete -
plaster
clay tile
brick or other masonry
units-
gypsum block -
gypsum wallboard -
mastic coatings -
mineral and fiberboard -
mineral wool
What happens when there is no fire-protection material applied to steel beams or joists that support floors or roofs? ISO still considers a building modified fire resistive if it has a suitable ceiling. Ceilings can be plaster or gypsum wallboard or suspended mineral tile. The entire floor-ceiling (a fire-resistive ceiling protecting a floor) or roof-ceiling (a fire-resistive ceiling protecting roof supports) should conform to construction details in a UL-listed or Factory Mutual (FM)-approved design. ISO individually evaluates each approved design.
Advantages of
the modified fire
resistive construction:
uses noncombustible
materials
allows greater height
and area than other
construction classes
uses load-bearing
members or assemblies
that resist damage from
fire
expensive to construct and repair
provides a false sense of security
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