7 FireResistive Construction 1st part

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Session 12 Codes Ermal Shpuza
7 Fire-Resistive Construction (1st
part)
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Fire-Resistive Construction
According to 702, fire-resistive rating is
defined as the period of time that a building
element, component or assembly maintains the
ability to confine a fire, continues to perform
given structural function, or both as determined
by tests or methods prescribed in 703. The
time-rating in hours indicates how long a
building material, element or assembly can
maintain its structural integrity and/or heat
transfer resistance in a fire, and correspond to
the construction type designations in Chapter 6
of IBC.
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Fire-Resistive Construction
Whether passive or active, fire-resistive
construction, has two primary purposes. The
first is the protection of the building
structure. Such protection is typically applied
directly to structural members. The second is
the separation of spaces to prevent the spread of
fire or smoke within a building and the spread of
fire between buildings. The protection of spaces
addresses fire or smoke impacts on larger-scale
building systems, such as floors, walls and
ceilings as well as openings in these systems.
According to 702, fire area is defined as the
aggregate floor area enclosed and bounded by
fire walls exterior walls fire-resistance-rated
horizontal assemblies of a building.
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Fire-Resistive Construction
Exception to 703.2 allows exterior bearing wall
rating requirements to equal those for
non-bearing walls when all factors such as fire
separation and occupancy are considered. This
exception recognizes that fire-resistance in
exterior walls is concerned with stopping the
spread of fire as well as protecting the
structure. The code recognizes that there is no
point in protecting the structure to a higher
level than is required for the walls enclosing
the space, since the governing criteria is the
prevention of fire outside the building. With
regard to the ability of structural members to
expand or contract under fire conditions, the
definition of ASTM E 119 assume that tested
materials are not restrained. Hence, assemblies
considered as restrained typically have a higher
hourly rating with less application of fire
protection and are thus attractive to use in
design. The difficulty of designing and proving
that assemblies are truly restrained very often
outweighs any advantages gained in reducing the
quantities of fire-protection materials used.
Advise follow the code sections assuming that
all assemblies are unrestrained when determining
the fire-resistance requirements.
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Alternative Methods to Determining Fire Ratings
703.3 allows designers to use several other
methods to ASTM E 119 to determine hourly
ratings. Use ratings determined by Underwriters
Lab or Factory Manual. Table 719 gives a list of
protection measures that can be applied to
different building elements. 720 allows the
designer to calculate the fire-resistance of
assemblies by combining various materials, hence
giving a greater flexibility to meet the actual
design conditions than the prescriptive set of
assemblies of Table 719. 703.3 allows
engineering analysis based on ASTM E 119 to be
used to determine projected fire-resistance. This
is based on extrapolations of test results to
predict performance of systems without undergoing
full-scale fire test. 703.4 recognizes that
certain combinations of combustible and
noncombustible materials may be considered as
noncombustible if they meet noncombustibility
test criteria.
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Organization of Chapter 7
Code sections take the form of statements and
exceptions. The code is organized to move from
the exterior of the building to areas inside the
building and then to the structure. The first set
of assemblies can be thought of as planes, both
vertical and horizontal, arranged around the
structural system. These planes may be bearing
walls and part of the structural system, or they
may be curtain walls or interior partitions
independent of the structure. There are various
interrelated conditions that impact the
fire-resistance requirements of the systems.
Openings (and their protections) Location on the
property Relationships of exterior walls facing
each other (as in courts) Separation of interior
spaces by fire walls Vertical circulation,
vertical openings Protection of egress
paths Smoke barriers Penetrations by utility
systems Abutment of floor systems with
curtain-wall systems Fire-resistive protection of
structural systems.
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Exterior Walls - Projections
704.2 governs the extent of allowable
projections according to their relationship to
property line. The combustibility of
projections is governed by the wall construction
type (which is related to height, areas and
occupancy types). In cases when opening in the
exterior walls are prohibited or opening
protection is required by location on property,
any combustible projection must be of 1-hour
construction, even in unrated buildings.
Projections include such elements as eave
overhangs, cornices and balconies that extend
beyond the floor area.
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Exterior Walls Projections Limited by 1st Method
Exterior or interior property line Required
fire-separation distance (L) 704.2 limits
projections by the following two methods First
Method 1/3L maximum projection toward the
property line, beyond the assumed vertical plane
where protected openings are required as
determined in accordance with Table 704.8
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Exterior Walls Projections Limited by 2nd Method
Second Method 12 maximum projection into area
where openings are prohibited, Required
fire-separation distance Exterior or interior
property line Assumed vertical plane as
determined in accordance with Table 704.8
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Exterior Walls Multiple Buildings
704.3 assumes a property line between buildings
or elements for multiple buildings on a site or
configurations that create courts. No
specification is given for the position of the
line midway between buildings, hence the designer
is free to locate the interior property line at
any point as long as the wall protection
requirements are met. The intent of this
section is to prevent the spread of fire by
radiant heating or convection.
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Exterior Walls Fire Resistance Ratings
Two or more buildings on the same property may be
treated as separated buildings with an assumed
property line between. Note that distances need
not be equal. If the buildings are treated as
portions of a single building, the aggregate area
of the building must be within the limits
specified in Chapter 5. 704.3 assumes that
the court walls of buildings more than one story
in height have a property line between them.
Opening protectives are not required in court
walls if no more than 2 levels open onto the
court, the aggregate area of the building
(including the court) is within the allowable
area, and the building in not a Group I occupancy.
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Exterior Walls Fire Resistance Ratings
704.5 specifies that exterior walls having
a fire-separation distance gt 5 should be rated
for exposure to fires from the inside. Exterior
walls having a fire-separation distance lt 5
must be rated for exposure from both sides.
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Exterior Walls Openings
704.7 contains detailed calculation for
determining the fire-resistance rating of
protected openings (Equation 7-1) 704.8 and
Table 704.8 contain simpler calculations that
relate the location on property to the percentage
of wall openings and to whether the opening
should be protected or not. Note that, 704.12
allows opening protection to be provided by an
approved water-curtain exterior sprinkler along
with a conventional interior fire-sprinkler
system. This is an active measure that provides a
substitution for passive protection. Additional
passive or active fire-protection measures can
also allow increases in the allowed area of
openings.
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Exterior Walls Openings
Equation 7-2 in 704.8 allows the designer to
determine the amount of openings allowable given
the relationship of protected versus unprotected
openings under site and building conditions. A/a
Au/au lt 1 A actual area of protected
openings a allowable area of protected openings
as per Table 704.8 Au actual area of
unprotected openings au allowable area of
unprotected openings as per Table 704.8 704.8.2
allows unlimited unprotected openings in the 1st
floor of exterior walls if the exterior walls
face a public street and have a fire-separation
distance gt 15, or if they face an unoccupied
spaces that is at least 30 wide and has access
from a street to a posted fire lane.
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Exterior Walls Vertical Separation of Openings
704.9 regulates the vertical relationship
between openings. These restrictions do not apply
for buildings with lt3 stories in height and when
fire sprinklers are provided. If openings in
adjacent stories are lt5 of each other and the
lower one is unprotected, 704.9 requires that
they be separated vertically at least 3 by an
assembly of gt 1-hour rating. or by a flame
barrier that extends horizontally gt30 beyond
the exterior wall.
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Exterior Walls Vertical Exposure
704.10 requires the protection of openings in
any wall of multiple buildings in the same
property that extend above an adjacent roof. This
protection can be provided in various ways by
distance, by opening protectives, or by
protection of the roof framing and its supporting
structure. Approved protectives are required
for openings lt15 vertically above the roof of
the adjacent structure. for a horizontal fire
distance within 15 of the adjacent structure.
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Exterior Walls Parapets
704.11 makes a general statement that parapets
should be provided at exterior walls of
buildings. Their purpose is to impede the spread
of fire from one building to another by providing
a barrier to fire and radiant heat transfer in
case the fire breaks through the roof
membrane. The exceptions that follow reduce or
eliminate the need for parapets in case
conditions are met. These exceptions become the
code criteria rather than the general statement
that parapets will always occur.
Typically parapets are to extend gt30 above the
roof and be on the same construction as the wall
supporting them
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Exterior Walls Parapets - Exceptions
No parapets are needed where The wall satisfies
the fire-separation distance criteria in
accordance with Table 602 The building area is
lt1,000 sf on any floor The roof construction is
entirely noncombustible or of at least 2-hour
fire-resistive construction The roof framing is
protected against the fire exposure from the
inside (see next slide) In residential
occupancies, a fire barrier is provided by
sheathing the underside of the roof framing, or
the roof sheathing is of noncombustible materials
for 4 back from the roof/wall intersection When
gt25 of openings are allowed to be unprotected
according to 704.8 due to the buildings
location from a property line.
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Exterior Walls Parapets
No openings are permitted within 5 of
fire-resistance-rated exterior walls in Groups R
and M. A separation of 10 is required for other
occupancies. 1-hr rating roof/ceiling
framing parallel to exterior wall 4 minimum for
Groups R and M and 10 for other occ. When not
parallel to exterior walls, the entire span of
roof/ceiling framing should be of gt 1-hr rated
construction unrated wall due to
fire-separation distance
Parallel to exterior
1-hr rated exterior wall
Not parallel to exterior
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Fire Walls
702 defines a fire wall as a fire-resistance-rate
d wall which purpose is to restrict the spread of
fire. A fire wall must extend continuously from
the building foundation to and through the roof,
and have sufficient structural stability to
withstand collapse if collapse of construction on
either side of the fire wall occurs. Structural
Stability 705.2 requires that fire walls have a
structural configuration that allows it to stay
in place for the time required by the fire
rating Materials 705.3 requires fire walls to
be constructed of noncombustible materials,
except Type V construction. Fire-Resistance
Ratings 705.4 bases the required fire-resistance
ratings of fire walls on occupancy. For most
occupancies, fire walls are required to be 3-hr
rating. Table 705.4 allows 2-hr ratings in Type
II or V buildings for certain occupancies. In
case a fire wall separates different occupancies,
the most stringent requirements will
apply. Horizontal Continuity 705.5 requires the
fire walls to be continuous horizontally from
exterior wall to exterior wall, and extend gt18
beyond the exterior surface of exterior walls.
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Fire Walls
705.1 considers each portion of a building
completely separated by one or more fire walls to
be a separate building. Fire wall. If located
on a property line and serving as a party wall,
the fire wall is not allowed to have openings.
705.5 requires a fire wall to extend gt 18
beyond the exterior surface of exterior walls.
There are exceptions based on the provision of
additional fire-resistive construction at the
exterior wall to provide a barrier heat and flame
propagation.
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Fire Walls Exceptions to 18 Extension
A fire wall may terminate at the interior surface
of exterior sheathing, siding or other finish if
fire-rated protection forms a T and extends a
horizontal distance of at least 4 on both sides
of the fire wall. The fire-rated protection
may be provided by exterior-wall construction
having a rating of gt 1 hr, or by the use of
noncombustible exterior sheathing, siding or
other finish. 705.5 also allows a fire wall to
terminate at the interior surface of
noncombustible exterior sheathing if the building
on each side of the fire wall is protected with
an automatic sprinkler system.
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Fire Walls Horizontal Projections
705.5.2 requires fire walls to extend to
the outer edge of horizontal projections, such as
roof overhangs and balconies, that are within 4
of the fire wall. There are 3 exceptions to
this requirement
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Fire Walls Horizontal Projections - Exceptions
(1) The extension is not required when horizontal
projecting elements have no concealed
spaces. The exterior wall behind and below such
horizontal projections, however, must be of
minimum 1-hr rated construction for a distance gt
than the depth of projection on each side of the
fire wall. In addition, any openings in the
fire-rated exterior wall must have a
fire-protection rating of gt ¾ hour.
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Fire Walls Horizontal Projections - Exceptions
(2) If noncombustible horizontal projection have
concealed spaces, a minimum 1-hr
fire-resistance-rated wall must extend through
the concealed spaces. As in the case (1), the
projection must also be separated from the
building by a minimum of 1-hr rated construction
for a distance on each side of the fire wall
equal to the depth of the projection. (3) If
combustible horizontal projections have concealed
spaces, the fire wall must extend through the
concealed spaces to the outer edges of
projections. The exterior wall behind and below
the projections must be of a minimum 1-hr rating
for a distance gt the depth of projection in each
side of the fire wall.
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Fire Walls Vertical Continuity
705.6 requires that fire walls be continuous
vertically from the building foundation to a
point gt 30 above adjacent roofs. No
horizontal offsets in the fire wall are
permitted. The fire wall for a building located
above a parking garage in accordance with 508.2
extends from the horizontal separation between
the parking garage and the building above.
Where the fire wall meets the roof construction,
same principles for the T junctions between FW
and exterior wall apply. It is best to presume
that fire protection of roof construction extends
to a minimum of 4 on each side of the FW when
framing is parallel to the wall and to the entire
length of the span when framing is perpendicular
to the wall.
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Fire Walls Vertical Continuity Exceptions to
30 Above
Not less than Class B roof covering The entire
span of the roof framing perpendicular to a FW
must have a 1-hr rating. Roof framing parallel
to a FW must have gt 1-hr rating within 4 of
FW Roof framing must be supported by bearing
walls or columns and beams with 1-hr rating No
openings are permitted within 4 of FW 2-hr
FW Not less than Class B roof covering Noncombus
tible roof sheathing, deck or slab FRT wood
permitted within 4 of FW in Types III, IV and V
construction No openings within 4 from FW
perpendicular
parallel