6 Types of Construction contd

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Session 10 Codes Shpuza
6 Types of Construction (contd)
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Types of Construction
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Types I and II of Construction
The building elements of Type I and Type II
construction are of noncombustible materials. The
definition of noncombustible material is
contained in 703.4 and requires meeting the
criteria of ASTM E 136. Type I-A, providing the
highest level of fire-resistance-rated
construction, requires passive protection for all
elements of the structure Type I-B is similar to
Type I-Am but permits a 1-hr reduction in
fire-resistance rating for the structural frame,
bearing walls and floor construction, and a ½ hr
reduction for roof construction. Type II-A
construction allows active or passive protection
of all elements of the structure. Type II-B
construction allows unprotected noncombustible
building elements. Before this was described as
Type II nonrated.
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Combustible Materials in Types I and II
Construction
The key to the use of combustible materials in a
noncombustible construction type is understanding
that these uses are ancillary to the primary
structure of the building. The premise for
allowing the use of these combustible materials
is that they will be of limited quantity and used
under defined conditions where they will not
contribute in any large measure to compromising
the desired level of fire-resistance in the
structure. There are a number of exceptions
providing the use of combustible materials in
Type I and Type II constructions.
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Exceptions for Combust. Materials in Type I and
Type II
603 contains a list of notes specifying which
combustible materials can be used in buildings of
Type I and Type II constructions. 1 Reiterates
allowances for the use of fire-retardant-treated
FRT wood for non-bearing walls and partitions and
for the roof construction noted in the footnotes
of Table 601. 2 Materials with a flame spread of
less than 25 have ratings corresponding to Class
A interior finishes per ASTM E 84. These indices
may be higher, as noted in the exception, where
insulation is encapsulated between layers of
noncombustible materials without an air space.
3 Foam plastics are allowable of complaint with
the provisions of Chapter 26 of the IBC. 4 Most
of roof coverings have a classification or A, B
or C, so this should almost always be workable.
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Exceptions for Combust. Materials in Type I and
Type II
5 IBC recognizes that combustible decorative and
utilitarian interior finishes such as wood
floors, will be applied over the noncombustible
structural elements. 6 Wood trim at or near
grade level is acceptable if it is not beyond
ready fire-fighting access up to a level of 15
above grade.. 7 Fire-stopping is required in
wood floors in Type I and II construction.
8 The key to this section is that the area in
question be occupied and controlled by a single
tenant. Also, these partitions must not define
exit access passages that could be construed as
corridors for the use of more than 30 occupants.
Single tenant floors can have partitions of wood
or similar light construction if they are lower
than 6 and allow standing occupants to generally
survey the occupied space in the event of
emergency. 9 Platforms are defined in 410 as
raised areas used for worship, lectures, music
plays or other entertainment.
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Exceptions for Combust. Materials in Type I and
Type II
10 These refer to incidental materials defined in
602 of IMC. 11 Provisions from Chapter 14,
Chapter 26 and Chapter 7 that regard the
fire-separation and fire-resistive properties of
combustible veneers in projections from exterior
walls. 12 Combustible blocking and nailers are
incidental to the structural fire-resistance of
the building as a whole. This note acknowledges
the necessity for their usage. 13 Plastic
glazing materials are permitted in conformance
with the requirements of Chapter 26. 14 Similar
to Note 12 15 Decorative plastic veneer is
allowable if installed in accordance with
requirements of Chapter 26.
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Exceptions for Combust. Materials in Type I and
Type II
16 Similar to Note 12. 17 This is a
cross-reference to Footnote C of Table 601 and is
redundant. 18 These aggregates are allowed to be
combustible provided that the assembly meets the
fire-resistance-test criteria of the IBC.
19-22 These exceptions allow for combustible
materials to be used if they meet specific
criteria spelled out in other sections of the
IBC.
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Exceptions for Combust. Materials in Type I and
Type II
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Type III Construction
Type III buildings are a mix of noncombustible
and combustible elements, having noncombustible
exterior walls and combustible interior
construction. These building types arose in the
US in late 1800s out of the need to end
conflagrations that struck congested business
districts such as Chicago. The buildings were
designed to prevent a fire from spreading from
one building to another by igniting the exterior
wall of adjacent buildings.
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Type III Construction
Type III buildings are a mix of noncombustible
and combustible elements, having noncombustible
exterior walls and combustible interior
construction. These building types arose in the
US in late 1800s out of the need to end
conflagrations that struck congested business
districts such as Chicago. The buildings were
designed to prevent a fire from spreading from
one building to another by igniting the exterior
wall of adjacent buildings.
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Type III Construction
The construction materials on the exterior of a
Type III building are required to be of
noncombustible materials. FRT wood is allowable
in the exterior walls where the required
fire-resistance rating is 2 hrs or less. Table
601 requires 2hr walls for Type III-A buildings,
thus FRT wood is acceptable except where this is
superseded by the requirements of Table 602 based
on the fire separation distance. This would only
occur in Group H occupancies with a
fire-separation distance of of less than
5. Type III buildings are considered
combustible since the IBC allows their interior
building elements to be of combustible materials
and also to be of unprotected construction of
allowed by the building height and area
allowances based on occupancy.
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Type IV Construction
Type IV buildings came about to address
fire-safety conditions for manufacturing and
storage, as Type III did for office and
residential occupancies. It is also known as
mill construction. They utilized heavy
timber HT structural members and heavy wood floor
decking inside of exterior walls of
noncombustible construction. Many of these
buildings have also movable heavy metal shutters
to close off exterior openings to prevent a fire
to propagate from outside or into the neighboring
building.
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Type IV Construction
The criteria for HT construction are based on the
past performance of historical construction, not
on the scientific rationales of ASTM E 136 and E
119. Type III buildings burn slower under fire
conditions. As the charring of the HT members
continues, it retards further deterioration of
the wood members by insulating the core of the
wood from the fire. This type of construction
utilizes heavy-sawn timbers in older buildings,
but likely will use glued-laminated structural
wood members in modern construction.
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Type IV Construction
A key element of HT construction is that there
are no concealed spaces in the building elements.
This prevents the development of unobserved
fires. This would prevent sudden structural
collapse. Lumber sizes are called out as nominal,
hence the actual dimensions of wood members will
be smaller. Ex. 8x8 nominal 7 ¼x7 ¼
actual. Floor framing requires a minimum nominal
thickness of 3 and floor are required to be held
away from the exterior wall but blocked with
fire-blocking or corbeling under floor members.
Sprinkler substitutions criteria for the roof
of HT buildings are contained in 602.4.3 and not
called in footnote d of Table 601 like other
constructions. Also, the separation criteria for
HT buildings are noted in 602.4.7 and not in
Table 602 like other types of construction.
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Type V Construction
Type V construction is the least restrictive
construction type. It allows the use of any
materials permitted by the IBC. A typical example
is the conventional light-wood-framed single
family residence. Due to the fact that elements
are combustible, the fire resistance of building
elements is typically provided by the application
of fire-resistance materials to the building
parts. Type V-A construction is a protected
construction, hence all major building elements
must have a 1hr rating. Type V-B construction is
unprotected and requires no fire-resistance
ratings except where 602.1 and Table 602 require
exterior wall protection.