Use Groups
| Group |
Designation |
Use |
| Assembly (A) |
A-1 |
Assembly uses intended for the production and viewing of performances,
such as theaters and concert halls, including motion picture theaters. |
| |
A-2 |
Assembly uses intended for food or drink consumption, such as restaurants,
banquet halls, and taverns. |
| |
A-3 |
Assembly
uses not classified in other categories; assembly uses such as
churches, exhibition halls and
galleries,
and libraries. |
| |
A-4 |
Assembly uses intended for viewing of indoor sporting events, such
as enclosed
stadiums, ice skating rinks, and arenas. |
| |
A-5 |
Assembly uses intended for outdoor activities such as grandstands
and stadiums. |
|
| Business (B) |
B |
Uses for office and service activities, such as office
buildings, banks, and barber shops,
including
education uses above the 12th grade. |
|
| Educational (E) |
E |
Educational uses (classrooms) for children through the 12th grade,
including certain day care uses. |
|
| Factory (F) |
F-1 |
Factory and manufacturing uses for all goods which are combustible
but not classified as hazardous. |
| |
F-2 |
Factory and manufacturing uses for goods which are noncombustible,
such as
metal products, beverages, and glass products. |
|
| High Hazard (H) |
H-1 |
Buildings which contain materials that are detonation hazards,
such as explosives. |
| |
H-2 |
Buildings which contain materials that are deflagration hazards,
such as
flammable and combustible liquids in open containers. |
| |
H-3 |
Buildings which contain materials that would readily support combustion,
such as flammable and combustible liquids in closed containers, consumer
fireworks,
and certain oxidizers. |
| |
H-4 |
Buildings which contain health hazards such as corrosives and toxic
materials. |
| |
H-5 |
Semiconductor fabrication facilities and similar uses which use
materials
defined as hazardous production materials (HPM). |
|
| Institutional (I) |
I-1 |
Supervised care facilities housing persons that are capable of
responding to emergency situations without assistance, such as assisted
living facilities, group homes, and rehab centers, housing more than
16 occupants. |
| |
I-2 |
Buildings used for medical and psychiatric care in which occupants
may not be capable of self-preservation in the case of an emergency,
such as hospitals
and nursing homes. |
| |
I-3 |
Buildings inhabited by persons under restraint, such as prisons. |
| |
I-4 |
Buildings occupied by persons under custodial care for less than
24 hours,
such as adult and infant day-care. |
|
| Mercantile (M) |
M |
Buildings used for the display and sale of merchandise, including
associated storage areas, such as department stores and shops, and
including
gasoline service stations. |
|
| Residential (R) |
R-1 |
Buildings housing occupants that are transient in nature, such
as hotels. |
| |
R-2 |
Multi-family residential buildings
such as apartment buildings, dormitories, and fraternities/sororities.
(Note: Townhouses, as defined
in the International Residential Code (IRC), are not
within the scope of the International Building Code (IBC).) |
| |
R-3 |
Residential occupancies containing not more than two dwelling units,
and day care facilities for fewer than 6 persons. (Note: In the IBC,
the R-3 designation applies primarily to dwellings that are attached
to other occupancies. Detached single family, two-family, and townhouse
buildings are outside of the scope of the IBC, and are regulated
by the IRC.) |
| |
R-4 |
Residential care/assisted living facilities for between 6 and 16
occupants, such as halfway houses and group homes in which occupants
are capable of self preservation without physical assistance in the
case of an emergency. |
|
| Storage (S) |
S-1 |
Buildings used for storage of all goods that are combustible but
not classified as hazardous, and includes motor vehicle repair garages. |
| |
S-2 |
Buildings used for the storage of goods which are essentially noncombustible,
such as food products, glass, and metal items, packaged and stored
with a limited amount of combustible packaging, and includes parking
garages. |
|
| Utility and Miscellaneous (U) |
U |
Buildings of an accessory
character, agricultural structures, and buildings not classified
in other occupancies, such as barns, greenhouses,
and stables. |
|
| Mixed Use |
|
When a building contains
several different occupancy groups, it must
be classified as a “mixed use” or “mixed occupancy” building.
For instance, school buildings which contain an auditorium or a cafeteria would
be a mixed use building with both E and A-3 occupancy groups. Table I compares
the methods for addressing mixed occupancy buildings.
Table I
Code Comparison - Mixed Uses and Occupancies
| Code Provisions |
IBC |
| Separated Uses |
Allows mixed occupancies if they
are separated as per 302.3.3 and the sum of the occupancy ratios1 does
not exceed one. |
| Non-separated Uses |
Allows uses to be unseparated within
a fire area2 if the fire area does not exceed the allowable height and
area for the type of construction, based on the more restrictive occupancy
group.
|
1. Occupancy ratios is the actual occupancy
floor area divided by the tabular area permitted for that occupancy group
in specific construction type.
2. Fire area is the aggregate floor area enclosed and bounded by exterior walls
or fire resistive building elements as defined in IBC Section 702.
Administrative offices in the same building
would be classified as occupancy group B. In fact, buildings with only a
single use group are relatively rare.
The code generally restricts building
size based on its use (occupancy group classification). When a building is
a mixed use building, there are two alternative approaches that can be used
to determine allowable building area, one of which incorporates a fire resistance
rated separation between the different use groups. Accordingly, under the
IBC, mixed occupancy buildings can be designated as either “separated
mixed use” or “non-separated mixed use,” depending on which
approach is chosen by the designer or building owner. |
| |
|
|
Types of Construction
Similar to the previous codes, construction type provisions are set out
in Chapter 6 of the IBC. The type of construction is determined by
two factors: 1) whether the materials used in the structural frame
are combustible or noncombustible, and 2) the fire resistance of building
elements. Noncombustible materials can have very little fire resistance,
(for instance, steel framing when subjected to a hot fire can fail
quickly), and so combustibility and fire resistance are separate determining
factors in type of construction.
In the IBC there
are five types of construction, and they are summarized in Table V.
Types III
through V are primarily wood frame construction;
Type III is wood frame with noncombustible or fire-retardant treated
wood exterior walls, Type IV is heavy timber, and Type V is generally
thought of as wood frame. The “A” designation in these construction
types means the building elements for the most part are required to be
of one-hour rated construction. The “B” designation means
that no fire resistance rating is required (referred to as “unprotected” wood
frame construction).
Table V
Types of Construction
in the IBC
| General Description |
IBC Description |
| Nonconbustible |
Type I ( A & B)
|
| |
Type II (A) |
| |
Type II (B) |
|
| Mixed noncombustible and combustible |
Type III (A) |
| |
Type III (B) |
|
| Combustible - heavy timber and traditional wood frame |
Type IV (Heavy Timber) |
| |
Type V (A) |
| |
Type V (B) |
| |
|
Even
in the noncombustible construction types (Types I and II), many nonstructural
elements of the building, such as floor coverings, windows and doors,
and interior finishes, can be wood. Permitted combustible building
elements in noncombustible buildings are conveniently listed in Section
603 of the IBC. This list includes structural elements that are constructed
of fire retardant treated wood (FRTW). FRTW is not considered noncombustible,
but can often be used in place of noncombustible materials. For instance,
FRTW can be used in place of noncombustible materials in exterior walls
of Type III buildings, and in roof structures of low-rise buildings
of Types I and II construction. Table VI summarizes where fire-retardant
treated wood is permitted to be used in lieu of noncombustible materials.
Table VI
Allowable Use of Fire Retardant Treated Wood in the IBC
IBC
Construction Type |
Building
Assembly |
IBC |
| Type I and
II Construction |
Roof structures |
Permitted in
buildings not over two-stories (Table 601, note c3). |
| |
Exterior walls |
Permitted when
the wall is non-load bearing and a fire rating is not required
(Section 603.1.1.2). |
| |
Interior walls |
Permitted in
non-load bearing partitions where the fire rating is 2 hours or
less (Section 603.1.1.1). |
|
| Type III and
IV Construction |
Exterior walls |
Permitted in
exterior walls when
the required rating is 2-hours or less. |
|
| Type V Construction |
All Assemblies |
Use
of
FRTW is unrestricted. |
| |
|
|
In Section 602.3, the IBC defines Type III Construction as being “that
type in which the exterior walls are of noncombustible materials and
the interior building elements are of any material permitted by the code.” The
section goes on to say that fire-retardant treated wood is permitted
in exterior wall assemblies in lieu of noncombustible materials when
the rating of the wall is required to be 2-hours or less. Therefore,
for many of the most common occupancies, buildings constructed entirely
of wood can be just as large and as high as noncombustible buildings.
Table VII shows that buildings of IBC Type III-B in many occupancies
may be just as large as buildings of Type IIB (noncombustible unprotected).
Buildings of Type III-B, for the occupancies shown, may be entirely of
wood if FRTW is used in the exterior walls.
Table VII
Comparison of IBC Type IIB and Type III Construction -
Allowable Areas and Heights
IBC
Occupancy Group |
Table
503
Base Allowable Area
(sq ft) |
Table
503
Base Allowable Height
(stories/feet) |
| |
|
| |
Type IIB |
Type IIIB |
Type IIB |
Type IIIB |
| A-3 |
9500 |
9500 |
2/55 |
2/55 |
| B |
23000 |
19000 |
4/55 |
4/55 |
| E |
14500 |
14500 |
2/55 |
2/55 |
| M |
12500 |
12500 |
4/55 |
4/55 |
| R-1 |
16000 |
16000 |
4/55 |
4/55 |
| R-2 |
16000 |
16000 |
4/55 |
4/55 |
| S-1 |
17500 |
17500 |
3/55 |
3/55 |
| |
|
|
|
|
The area and height modifications
discussed below for sprinklers and open space are applicable to these
values.
Building
and Property Geometry Definitions
| AREA,
BUILDING |
The
area included within surrounding exterior walls (or exterior walls
and firewalls) exclusive of vent shafts and courts. Areas of the
building not provided with surrounding walls shall be included
in the building area if such areas are included within the horizontal
projection of the roof or floor above. |
| BASEMENT |
That portion
of a building that is partly or completely below grade plane (see “Story
above grade plane” in IBC Section 202). A basement
shall be considered as a story above grade plane where the finished
surface
of the
floor above the basement is:
1. More than 6 feet above grade plane; or
2. More than 12 feet above the finished ground level at any point. |
| GRADE PLANE |
A reference
plane representing the average of finished ground level adjoining
the building at exterior walls. Where the finished ground level
slopes away from the
exterior walls, the reference plane shall be established by the lowest points
within the area between the building and the lot line or, where the lot line
is more than 6 feet from the building, between the building and a point
6 feet from the building. |
| HEIGHT, BUILDING |
The vertical
distance from grade plane to the average height of the highest
roof surface. |
| HEIGHT, STORY |
The vertical
distance from top to top of two successive finished floor surfaces;
and, for the topmost story, from the top of the floor finish to
the top of the ceiling joists or, where there is not a ceiling,
to the top of the roof rafters. |
| MEZZANINE |
An intermediate
level or levels between the floor and ceiling of any story and
in accordance with IBC Section 505. |
| FLOOR AREA, GROSS |
The floor area
within the inside perimeter of the exterior walls of the building
under consideration, exclusive of vent shafts and courts, without
deduction for corridors, stairways, closets, the thickness of interior
walls, columns or other features. The floor area of a building,
or portion thereof, not provided with surrounding exterior walls
shall be the usable area under the horizontal projection of the
roof or floor above. The gross floor area shall not include shafts
with no openings or interior courts. |
| FLOOR AREA,
NET |
The actual
occupied area not including unoccupied accessory areas such as
corridors, stairways, toilet rooms, mechanical rooms and closets. |
| PUBLIC WAY |
A street, alley
or other parcel of land open to the outside air leading to a street,
that has been deeded, dedicated or otherwise permanently appropriated
to the public for public use and which has a clear width and height
of not less than 10 feet . |
| OPEN SPACE |
Undefined in the IBC and IRC. This term is interpeted differently
between the three legacy codes. Check with the building official
for local interpretation of OPEN SPACE. |
| OPEN PERIMETER |
Exterior
perimeter of the building that directly faces open space. |
| PERIMETER, EXTERIOR |
Distance around the extreme
exterior face of the building envelope of the building. |
Height & Areas
Determination
Increased allowable building height and area (H&A) provisions of
the IBC are calculated as follows:
Where:
Aa = Allowable gross area per floor (sq. ft.)
At = Tabular gross area per floor (sq. ft.) [IBC Table
503 values]
If = Area Increase due to frontage (percent)
Is = Area increase due to sprinkler protection (percent)
(The ratio W/30 is permitted to be 2 for A-1, A-4, B, F, M, and S; 1
for all other use groups)
And:
Where:
P = Exterior perimeter of the entire building (ft.)
F = Exterior building perimeter which faces open space -
a minimum of 20 ft. in width (ft.)
W = Minimum
weighted width of public way or open space (ft.) (see
below).
Note W/30 is not to exceed 1.0 in If formula (or W < 30).
n = number of exterior perimeter
segments fronting public way or open
space.
If Wi < 20 ft., then use Pi = 0 in weighted
average calculation.
If Wi ≥ 30 ft., then use Wi = 30 ft. in weighted
average calculation.
Other
IBC Criteria
The
IBC permits sprinklered buildings with National Fire Protection
Association NFPA 13 systems to contain one additional story and be
increased in height
20 feet.
Residential
buildings with NFPA 13R systems may be increased one story and 20 feet
in height and are not subject to the total building area limit of a three
story building (13R is only appropriate up to four stories above grade
plane).
Use Group Separation
In
the IBC, a rated wall in accordance with Table 602 can be
used to separate a building into two smaller areas, neither of which
exceeds threshold
values that require installation of sprinklers. This is not considered
a fire wall separating buildings. It is a fire separation assembly,
separating the building into fire areas. In
addition, the IBC allows fire walls of combustible material in buildings
of Type V construction. This permits the structure to be divided into
separate buildings, each subject to its own height and area limits.
NFPA 221, the standard for fire walls and
fire barrier walls also has a provision for
a 2-hour fire resistance rated fire wall built using two contiguous
1-hour fire
resistance rated assemblies.
Unlimited Areas
Under the IBC, depending on the building's use, wood buildings of unlimited
area are permitted when 60-ft. spatial separation to the property
line is provided, the building is sprinklered, and the building
is constructed of Type III construction. Certain buildings, like
one-story, Group B, F, M, or S buildings, or a one-story Group A-4
building of other than Type V construction, are permitted to be unlimited
area when 60-ft. spatial separation to the property line is provided
and the building is sprinklered. The area of a two-story, Group B,
F, M, or S building shall not be limited when the building is equipped
throughout with an automatic sprinkler system, and is surrounded
and adjoined by public ways or yards not less than 60 feet in width.
Furthermore, buildings of
use
groups which might otherwise be permitted to be unlimited in area but
which lack a full 60 foot wide open perimeter can gain increased area
for widths from 30-ft. separation up to 60- ft. separation (W/30 =
2). Also, buildings with as little as 20-ft. fire separation get
credit for open perimeter. The calculator determines unlimited areas
within Sections 507.1 to 507.4 in the 2006 IBC. Sections 507.5 through
507.11 are beyond the calculator's scope at this time.
Larger Single-Story Buildings
The IBC allows the area for single-story buildings that are sprinklered
to be increased to 300% of the tabular area.
Fire Resistance Ratings
The IBC permits asymmetric testing for fire resistance rating
(testing from the inside only) where the distance to the property line
is at
least 5 feet.
IBC Table 720 now lists
I-Joist assemblies and nominal 2x exterior wall
assemblies rated at 100% load capacity. If sprinklering
is not used for H&A increases, it
is permitted to reduce fire resistive requirements by one hour for
all construction elements
except exterior walls.
Design Example
Case Study
1
Case Study
2
Reference
The basis of this
Help File can be found in:
Francis, Sam (2005): International
Building Code: More Options with Greater Opportunity for Wood-Frame
Design, Wood Design Focus, Madison,
WI, 15(4):12-16.
Francis,
Sam (2006): International Building Code: More Options with Greater
Opportunity for Wood-Frame Design, Structure,
October Issue, NCSEA / CASE / SEI, Copper Creek, Reedsburg, WI, 13(10):22-24.
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