AMERICAN FOREST & PAPER ASSOCIATION
American Wood Council
Engineered and Traditional Wood Products
BCD101:
Building Codes & Wood Design
Copyright © 2007 American Forest & Paper Association, Inc. All rights reserved.
Copyright © 2001, 2004, 2007 American Forest & Paper Association, Inc.
All rights reserved.
1
Copyright of Materials
This presentation is protected by US and International copyright laws.
Reproduction, distribution, display, and use of the presentation without
written permission of the American Forest & Paper Association /
American Wood Council is prohibited.
Copyright © 2001, 2007 American Forest & Paper Association, Inc.
All rights reserved.
3
BCD101 Learning Outcomes
•
At the end of this eCourse, you will be:
1. Familiar with building code requirements for
wood frame buildings
2. Familiar with International Building Code’s
allowable heights and areas
3. Functional with fire resistance issues such as:
•
•
•
•
Flame spread
Component Additive Method to determine fire
resistance
One-hour fire wall designs
Heavy timber fire resistance calculations
In this eCourse, we will engage in a discussion of building code
requirements for wood-frame buildings with an emphasis on the International
Building Code's allowable heights and areas. The course also discusses fire
resistance issues such as: flame spread performance, component additive
method of determining fire resistance, one-hour rated fire walls, and heavy
timber fire resistance calculations.
4
WOOD IN THE INTERNATIONAL
BUILDING CODE
Allowable Size
Fire Resistance
The purpose of this program is to discuss the way the International Building
Code addresses wood design and construction, specifically talking about
allowable building size and fire resistance.
5
“Traditional” Wood Buildings
Dwellings
Churches
Restaurants
Small Offices
When one thinks of wood-framed buildings, one often thinks of a handful of
uses, usually smallish buildings.
6
But With a Knowledge of Codes …
However, as we hope to show in this program, with a little bit of knowledge
about the code …
7
… Much More is Possible
… buildings beyond this group of “traditional” wood buildings are possible.
8
International Building Code
• Controls building size
• Regulates types of
materials
• Specifies fire
resistance
Among the ways that the IBC impacts and regulates the use of wood, these
three items are probably the most important to a designer. The International
Building Code: controls the building size, regulates the types and materials
of construction, and specifies fire resistance.
9
This Program
• Allowable heights & areas
• Fire resistance
• Flame spread
We’re going to talk about allowable building size, fire resistance, and flame
spread.
10
INTERNATIONAL BUILDING CODE
Heights & Areas
Let’s start with allowable building size.
11
HEIGHTS & AREAS
Section 503
• The height and area
for buildings of
different
construction types
shall be governed
by the intended use
of the building and
shall not exceed the
limits in Table 503
except as modified
hereafter.
Height and area of a building – as presented in Table 503 of the IBC -- is
governed by the intended use and the type of construction. Note the
reference to modifications.
12
INTERNATIONAL BUILDING CODE
Heights & Areas
• Allowable area based upon
– Use of building (occupancy group)
– Type of construction (materials used)
• Smallest MAXIMUM allowable area
In order to understand the process of determining the code-permitted size of
a building, it is necessary to know what the building is going to be used for
and what the building is going to be constructed of.
Keep in mind that the tabular numbers that are referred to in Table 503 are
the smallest of the limits or maximum and that those numbers can be
modified upwardly.
13
USE & OCCUPANCY CLASSIFICATION
Chapter 3
Chapter 3 contains the provisions pertaining to the Use and Occupancy
Classification, a factor in determining allowable heights and areas.
14
USE & OCCUPANCY CLASSIFICATION
Chapter 3
• Residential (R1 thru R4 – various types of
residential uses) - “typical” wood frame
• Assembly (A1 thru A5 – various types of
assembly uses)
• Business (B – generally offices)
• Mercantile (M – generally retail sales)
While this program is intended to show that the code will allow something
beyond the small, so-called “typical” wood building, there are occupancies
that lend themselves more to wood buildings than do others. Our example of
allowable building size will be based on an occupancy classification: Aassembly, B-business, and M-mercantile occupancies.
15
TYPES OF CONSTRUCTION
Chapter 6
Another consideration in allowable heights and areas is the type of
construction – the classification of the building based upon the materials
from which it is built.
16
TYPES OF CONSTRUCTION
Chapter 6
Types of construction, both combustible &
noncombustible, designated as
A – Protected construction
B – Unprotected construction
Types of construction are typically divided into combustible and
noncombustible classifications. The official designation of the types of
construction are further modified by the addition of the letters “A” or “B.” This
would be new terminology for users of the Uniform Building Code or the
Standard Building Code. “A” designates protected construction and “B”
designates unprotected construction in the IBC terminology. This is true for
both combustible and noncombustible construction.
17
Types I & II Construction
There are two designators for “noncombustible” types of construction in the
IBC. Type I is typically concrete or heavily protected steel structures. Type II
is typically steel, either lightly protected or, in the case of IIB construction,
unprotected.
18
Types I & II Construction
Noncombustible construction: Types I & II
• Defined as: “ . . . In which the building
elements listed in Table 601 [structural frame,
bearing & nonbearing walls, interior & exterior
walls, floor & roof construction] are of
noncombustible construction.”
The definition of these two types of construction would seem to say no wood
is allowed, although keep in mind that the definition addresses only certain
elements of the building. And there may be exceptions to this.
19
Types I & II Construction
Exceptions to noncombustible requirements
(Table 601 & Section 603)
• Heavy timber permitted where 1-hr rating is
required
• Fire retardant treated wood allowed in some
applications
In some instances heavy timber construction is permitted in Type I or Type II
construction because it has an inherent resistance to burn-through, and fire
retardant treated wood is permitted in many applications due to its special
properties - details will be discussed next.
20
Types I & II Construction
• Fire retardant treated wood permitted
–
–
–
–
Nonbearing partitions rated 2-hrs or less
Nonbearing exterior walls not required to be rated
Roof framing of buildings not more than 2 stories
Roof framing and decking when more than 20’
above floor (& and can be exposed)
Instances in which fire retardant treated wood is permitted to be used in
Type I and Type II construction include:
Nonbearing partitions rated for 2-hrs fire resistance rating or less
Nonbearing exterior walls not required to be rated
Roof framing of buildings not more than 2 stories
Roof framing and decking when it is more than 20’ above the floor
21
Types I & II Construction
Combustibles permitted
• Fire retardant treated
wood
• Thermal/acoustic
insulation
• Foam plastics
• Roof coverings
• Some show windows
• Partitions dividing
stores, offices, etc.
• Platforms
• Blocking
• Some exterior wall
coverings, balconies
Here are other areas where combustible materials are permitted in Type I or
Type II construction:
Fire retardant treated wood
Thermal or acoustic insulation
Certain foam plastics
Roof coverings
Some show windows
Certain partitions dividing stores or offices
Platforms
Blocking
Some exterior wall coverings and balconies
22
Type III Construction
Mixed construction: Type III
• Defined as “… In which the exterior walls are
of noncombustible materials & the interior
building elements are of any materials
permitted by the code.”
Type III construction permits a mixture of noncombustible and combustible
materials. Type III construction is defined as that construction “…In which
the exterior walls are of noncombustible materials and the interior building
elements are of any materials permitted by the code.” As you can see from
the definition, a Type III building may have exterior noncombustible walls
and will permit the rest of the building to be of combustible material. As we’ll
show in a moment, even greater portions of the building may be of
combustible material. Type III construction is a very flexible type of
construction for a designer and the allowable floor area, as we’ll
demonstrate, is nearly as large – or as large – as that permitted for Type II
construction.
23
Type III Construction
• Exterior walls are to be
of noncombustible but
fire retardant treated
wood is permitted
where fire resistance
rating is 2-hrs or less
• Interior elements,
including roof framing,
can be of untreated
wood.
In Type III construction, exterior walls are required to be of noncombustible
construction, however fire retardant treated wood is permitted to be used in
exterior walls when the fire resistance rating of those exterior walls is
required to be 2-hours or less. Interior elements, including roof framing, may
be of untreated wood. Keep in mind the 2-hour fire resistance rating for
something we’ll talk about in a moment.
24
Exterior Walls: Fire Resistance
Table 602 stipulates the minimum fire resistance rating of exterior walls, and
that rating is based on the distance from the property lines. Notice that for
“typical” wood frame uses or occupancy groups, exterior walls have to be
rated a maximum of 2 hours fire resistance rating. Remember, the exception
to Type III construction permits the use of fire retardant treated wood in
exterior walls that may be of 2-hr fire resistance rating or less. That
exception would permit almost any use, therefore, to qualify as a Type III
building using wood throughout – including fire retardant treated wood in the
exterior walls and untreated wood elsewhere. And, as we’ll see shortly,
those buildings will compete in size with Type II construction.
25
Type V Construction
Combustible construction
• Structural elements, exterior walls, and
interior walls are of any material permitted by
the code.
Type V Construction allows any material recognized by the code. Normally
this type of construction is thought of as all wood frame, but it would permit
the use of other materials if needed. It’s important to realize that simply
adding noncombustible elements to a Type V building doesn’t make it Type
II. As long as the building doesn’t exceed the height and area permitted for
that type of construction, it may be built of a mixture of materials and still be
classified as a Type V building.
26
International Building Code
ALLOWABLE HEIGHTS & AREAS
• Tabular heights and areas
• Methods of increase
• Resulting numbers
Now that we’ve established the concepts of type of construction and of
occupancy group, this portion of the program is going to talk about building
size as permitted by the code. We’ll talk about the heights and areas
contained in the table in the code, and how those numbers can be
increased, and then we will give some examples of how large numbers can
be for combustible buildings.
27
International Building Code
ALLOWABLE HEIGHTS & AREAS
• Tabular heights and areas (minimums)
• Methods of increase
• Resulting numbers
First we’ll look at the tabular areas contained in the IBC. It is important to
keep in mind that these numbers are the minimum – that is to say the
smallest maximum permitted area and maximum permitted height for a
building. Remember, they can be increased with certain modifications.
28
IBC Table 506
Noncombustible
Combustible
Here’s a portion of the IBC table that provides the tabular height and tabular
area figures for the code. It indicates the noncombustible types of
construction and the combustible types of construction to help you sort them
out.
29
IBC Table 506
This table is easily understood. It is based on the type of construction listed
across the top: Type I, Type II, Type III, Type IV, Type V, with each type’s
subcategory: A – protected or B – unprotected construction. It’s also based
upon the occupancy groups which are down the side of the table.
In our example shown here, we’ve chosen Type III construction and an
occupancy classification Group M. You will notice that the type of
construction has two subdivisions – A (for protected) and B (for unprotected)
construction. For this example we’ve chosen unprotected construction Type
IIIB.
The numbers below the construction type are allowable heights in feet. For
our example of an M/Type III building, we can see that it can be 55’ high. If
we go to the cell where the occupancy group row and the type of
construction column intersect we see two other numbers. One of them is the
allowable height in stories and the other is the square footage per floor. Our
example building can be four stories and 12,500 square feet per floor.
It’s important to note that the height limitations work together. If the building
is no more than 55’ high, the designer is not allowed to squeeze five stories
into that space even if it were possible. The limitation of our example is four
stories with an overall height no greater than 55’.
As has been said previously, this is the maximum height and area -- the
building can always be that size. As we will show in a moment, it can be
30
Tabular Heights & Areas
NONCOMBUSTIBLE
OCCUPANCY
COMBUSTIBLE
TYPE II
A
TYPE II
B
TYPE III
A
TYPE III
B
TYPE V
A
TYPE V
B
HEIGHT
S/Ft
3/65
2/55
3/65
2/55
2/50
1/40
A-2
AREA
15,500
9,500
14,000
9,500
11,500
6,000
5/65
4/55
5/65
4/55
3/50
2/40
B
HEIGHT
S/Ft
M
AREA
37,500
23,000
28,500
19,000
18,000
9,000
HEIGHT
S/Ft
4/65
4/55
4/65
4,55
3/50
1/40
AREA
21,500
12,500
18,500
12,500
14,000
9,000
Fire retardant-treated stud walls
Non-treated wood roof assembly
Non-treated interior wood framing
Here we’ve pulled out the tabular heights and areas for the three occupancy
groups we mentioned and show them to compare numbers for combustible
construction to those of noncombustible construction. Type IV, heavy timber
construction isn’t typical and has not been included in this discussion. Note
how closely the numbers of Type III construction are to those of Type II
construction.
In this example, remember that in Type III, fire retardant treated wood is
permitted to be used in exterior wall assemblies. Whereas, non-treated wood
is permitted in roof assemblies and interior framing.
31
International Building Code
ALLOWABLE HEIGHTS & AREAS
• Tabular heights and areas
• Methods of increase
• Resulting numbers
We’ve talked about the tabular areas and compared them to noncombustible tabular areas. We’ve mentioned that they are a maximum
allowable area but that this maximum may be even further increased. Let’s
talk about how they may be increased.
32
International Building Code
ALLOWABLE HEIGHTS & AREAS
• Tabular heights and areas
• Methods of increase
– Open frontage
– Sprinklers
• Resulting numbers
There are two methods of increasing tabular areas. One is to provide open
space around the building perimeter. The other is to include the use of
automatic sprinkler systems within the building.
33
Frontage Increase
Section 506.2
• Where a building
has more than 25
percent of its
perimeter on a
public way or open
space having a
minimum width of 20
feet, the frontage
increase shall be
determined in
accordance with
Equation 5-2
The tabular floor areas aren’t predicated on any perimeter condition.
However, if open space as you see above is provided, the numbers in the
tabular areas may be increased in accordance with an equation that we will
talk about. The increase is because additional space or increased frontage
prevents spread of fire from building to building or across property lines.
34
Frontage Increase
Section 506.2
• Open frontage around building
– Public way: Street, alley, or other … land open to
outside air leading to a street, that has been
deeded, dedicated, or otherwise permanently
appropriated to the public use ...
– Open space: Not defined
• Minimum width of 20’
• More than 25% of perimeter needed to get an
increase
Here are the conditions under which open space can result in added floor
area. Note that the open space is either to be a public way – which is
specifically defined in the code – or “open space,” which is undefined.
Although traditionally things like yards and parking lots have been accepted
as open space, since the term is undefined it is best to get the code official’s
interpretation of the space before including it in your own calculations for
these kinds of spaces.
35
Permitted Increase
Areas of Table 503 permitted to be increased (Equation 5-1):
A a = At +
A tI f
100
+
A tI s
100
Where:
Aa = Adjusted allowable area (sq. ft.)
At = Area per Table 503
If = Area increase due to open frontage
Is = Area increase due to sprinkler protection
This is the equation used to calculate the permitted increase in area for both
frontage and for sprinkler protection.
36
Frontage Increase
Frontage increase determined by Equation 5-2:
If = 100
F
P
- 0.25
W
30
Where:
If = Area increase due to frontage (percent)
F = Building perimeter fronting on public way or open space
P = Perimeter of entire building
W = Minimum width of public way or open space. Note W/30
not to exceed 1.0
The frontage increase in the allowable area equation, or If for frontage
increase is as shown:
Where:
If is the area increase due to frontage
F is the building perimeter fronting on public way or open space
P is the perimeter of entire building
W is the minimum width of public way or open space.
This quantity, W/30, may not exceed 1.0, except in certain cases listed in the
text of section 506.
37
Sprinkler Increase
Section 506.3
Is = Increase due
to sprinkler system
in building
Now let’s talk about the increase due to the addition of an automatic
sprinkler system into the building.
38
Sprinkler Increase
Automatic sprinkler systems (Section 506.3)
• Multi-story buildings: Is = 200%
• Single-story building: Is = 300%
• Sprinkler system must be in accordance with
Section 903.3.1.1
– NFPA 13 system
The automatic sprinkler increase factor, Is, is equal to 200% for multi-story
buildings and Is is equal to 300% for single-story buildings. The sprinkler
system must be in accordance with section 903.3.1.1.
39
International Building Code
ALLOWABLE HEIGHTS & AREAS
• Tabular heights and areas
• Methods of increase
• Resulting numbers
We’ve talked about the tabular height and the tabular area numbers
permitted by the IBC and about the two methods for increasing those
numbers. Let’s talk now about the resulting numbers when you apply the
modifications to the tabular areas.
40
Frontage Increase
Property line
Street
30’
30’
55’
60’
Street
Let’s consider an example of a building situated on a corner lot with setbacks
55’ from the centerline of the street on the east side, 60’ from the centerline
of the street on the south side, 30’ from the property line on the west side,
and 30’ from the property line on the north. Notice that for street frontage, we
measure to the centerline of the street.
41
Permitted Increase
Areas of Table 503 permitted to be increased (Equation 5-1):
A a = At +
A tI f
100
+
A tI s
100
Where:
Aa = Adjusted allowable area (sq. ft.)
At = Area per Table 503
If = Area increase due to open frontage
Is = Area increase due to sprinkler protection
Remember the equation we talked about which will be used to calculate the
increases for floor areas?
42
Frontage Increase
Frontage increase determined by Equation 5-2:
If = 100
F
P
- 0.25
W
30
Where:
If = Area increase due to frontage (percent)
F = Building perimeter fronting on public way or open space
P = Perimeter of entire building
W = Minimum width of public way or open space. Note W/30
not to exceed 1.0
To calculate the frontage increase portion of the equation for our example,
we have to use Equation 5-2.
43
Frontage Increase
Frontage increase determined by Equation 5-2:
W
30
= 100 x 0.75 x 1 = 75
If = 100 1.0 – 0.25
30
F
P
Where:
If = Area increase due to frontage (percent)
F = Bldg perimeter fronting on public way or open space
P = Perimeter of entire bldg
W = Minimum width of public way or open space. Note W/30
not to exceed 1.0
Here is the equation solved for our example. Our example building has
frontage on all four sides greater than 25 ft, so the ratio F/P is 1.0. Notice
that W = 30’ and not 60’ in the solution to this equation. That is because W is
the minimum width of the public way or open space, and it is equal to 30’ in
our example. But even if the minimum were 60’, the result wouldn’t change
because W/30 may not exceed 1.0, except in special cases defined in 506.
Here’s the result…
44
Permitted Increase
Areas of Table 503 permitted to be increased (Equation 5-1):
A a = At +
At75
100
+
0
Is
If
Where:
Aa = Adjusted allowable area (sq. ft.)
At = Area per Table 503
If = Area increase due to open frontage
Is = Area increase due to sprinkler protection
Therefore, the If for our example is 75 and our increase equation
becomes… (see slide for text). Notice that Is is zero at this point.
45
Frontage Increase
NONCOMBUSTIBLE
OCCUPANCY
HEIGHT
S/Ft
A-2
AREA
HEIGHT
S/Ft
B
AREA
HEIGHT
S/Ft
M
AREA
COMBUSTIBLE
TYPE II
A
TYPE II
B
TYPE III
A
TYPE III
B
TYPE V
A
TYPE V
B
3/65
2/55
3/65
2/55
2/50
1/40
15,500
27,125
9,500
16,625
14,000
24,500
9,500
16,625
11,500
20,125
6,000
10,500
5/65
4/55
5/65
4/55
3/50
2/40
37,500
65,625
23,000
40,250
28,500
49,875
19,000
33,250
18,000
31,500
9,000
15,750
4/65
4/55
4/65
4,55
3/50
1/40
21,500
37,625
12,500
21,875
18,500
32,375
12,500
21,875
14,000
24,500
9,000
15,750
In this table, we’ve taken those numbers for various occupancy groups and
show the tabular numbers, or the top number in a cell, and the result based
upon the frontage increase - the lower number in a given cell. Keep in mind
that these numbers are per-floor square footage permitted for the number of
floors allowed for that type of construction. For example, Type IIIB
construction for use group M, as we discussed earlier, has an allowable
tabular value of 12,500 square feet, however, in our open perimeter
example, as we just calculated, the increase would bring the total to 21,875
square feet per floor.
46
Adding a Sprinkler Systems
Continuing our example of modifications, what happens to the permitted
allowable area if we add a sprinkler system?
47
Permitted Increase
Areas of Table 503 permitted to be increased (Equation 5-1):
A a = At +
A tI f
100
+
A tI s
100
Where:
Aa = Adjusted allowable area (sq. ft.)
At = Area per Table 503
If = Area increase due to open frontage
Is = Area increase due to sprinkler protection
Remember our formula… (see slide). Notice that the tabular area (At) is
added to the increase from frontage and to the increase for sprinklers. So
both sprinkler increase and frontage or open perimeter increase are additive.
48
Sprinkler Increase
Automatic sprinkler systems (Section 506.3)
• Multi-story buildings: Is = 200%
• Single-story building: Is = 300%
• Sprinkler system must be in accordance with
Section 903.3.1.1
– NFPA 13 system
Remember again, the sprinkler increase factor, Is, is 200% for multiple-story
buildings and 300% for single-story buildings.
49
Height Increase for Sprinkler
Section 504
• Automatic sprinkler
increase
– 20’ increase
– One story increase
• Group R occupancies
– Can use NFPA 13R
– Cannot exceed 4 stories
or 60’
• Exceptions
– I-2 of IIB, III, IV, & V
– H-1, H-2, H-3, & H-5
Providing frontage around the building, as we saw in our previous example,
will gain additional floor area, but provides no additional height or does not
increase the number of stories permitted from tabular. With sprinklers,
however, not only do you get a floor area increase, which remember is
additive to that permitted for the frontage increase, but also results in
additional height as you see here. In “Legacy Codes,” as ICC calls them,
some of the Legacy Codes did not permit a simultaneous increase for height
and for area because of sprinklers. Whereas, other Legacy Codes did permit
the simultaneous increase for height and for areas resulting from the use of
sprinklers.
50
Permitted Increase
Areas of Table 503 permitted to be increased (Equation 5-1):
A a = At +
At75
100
+
At300
100
Is
If
Where:
Aa = Adjusted allowable area (sq. ft.)
At = Area per Table 503
If = Area increase due to open frontage
Is = Area increase due to sprinkler protection
If our example building were a single story building with a sprinkler system
installed in accordance with NFPA 13, the overall equation with If, for
frontage increase, and Is, for sprinkler increase, would be like this… (see
slide).
51
Sprinkler Increase
NONCOMBUSTIBLE
OCCUPANCY
A-2
B
M
COMBUSTIBLE
TYPE II
A
TYPE II
B
TYPE III
A
TYPE III
B
TYPE V
A
TYPE V
B
HEIGHT
S/Ft
3/65
4/85
2/55
3/75
3/65
4/85
2/55
3/75
2/50
3/70
1/40
2/60
AREA
15,500
27,125
73,625
9,500
16,625
45,125
14,000
24,500
66,500
9,500
16,625
45,125
11,500
20,125
54,625
6,000
10,500
28,500
HEIGHT
S/Ft
5/65
6/85
4/55
5/75
5/65
6/85
4/55
5/75
3/50
4/70
2/40
3/60
AREA
37,500
65,625
178,025
23,000
40,250
109,250
28,500
49,875
135,375
19,000
33,250
90,250
18,000
31,500
85,500
9,000
15,750
42,750
HEIGHT
S/Ft
4/65
5/85
4/55
5/75
4/65
5/85
4,55
5/75
3/50
4/70
1/40
2/60
AREA
21,500
37,625
102,125
12,500
21,875
59,375
18,500
32,375
87,875
12,500
21,875
59,375
14,000
24,500
66,500
9,000
15,750
42,750
Now in our table, we see another line for area added to the cells. This is a
result of the sprinkler increase. In our example, construction Type IIIB for
use group M, mercantile, the tabular permitted area was 12,500 square feet.
The permitted floor area, adjusted for the open perimeter, was 21,875
square feet per floor. Now, with the addition of a sprinkler system, the total
allowable area per floor is 59,375 square feet.
52
Sprinkler Increase
NONCOMBUSTIBLE
OCCUPANCY
A-2
B
M
COMBUSTIBLE
TYPE II
A
TYPE II
B
TYPE III
A
TYPE III
B
TYPE V
A
TYPE V
B
HEIGHT
S/Ft
3/65
4/85
2/55
3/75
3/65
4/85
2/55
3/75
2/50
3/70
1/40
2/60
AREA
15,500
27,125
73,625
9,500
16,625
45,125
14,000
24,500
66,500
9,500
16,625
45,125
11,500
20,125
54,625
6,000
10,500
28,500
HEIGHT
S/Ft
5/65
6/85
4/55
5/75
5/65
6/85
4/55
5/75
3/50
4/70
2/40
3/60
AREA
37,500
65,625
178,025
23,000
40,250
109,250
28,500
49,875
135,375
19,000
33,250
90,250
18,000
31,500
85,500
9,000
15,750
42,750
HEIGHT
S/Ft
4/65
5/85
4/55
5/75
4/65
5/85
4,55
5/75
3/50
4/70
1/40
2/60
AREA
21,500
37,625
102,125
12,500
21,875
59,375
18,500
32,375
87,875
12,500
21,875
59,375
14,000
24,500
66,500
9,000
15,750
42,750
Now we’d like to highlight the comparison in area for Type II-B construction
(unprotected steel, for example) and Type III-B construction (which can be
constructed with fire retardant treated wood exterior walls for our example
occupancies and untreated wood elsewhere in the structure). In many
instances the code will permit floor areas equal to – or nearly equal to – the
steel or masonry construction, giving the designer or building owner the
affordability and quick construction time benefits attendant to wood
construction while permitting buildings of similar size.
For example, in our use group M, the tabular area for Type IIIB is 12,500
square feet and for Type IIB the tabular area is an identical 12,500 square
feet. The increased area per floor due to open perimeter increase is 21,875
square feet for each type – Type IIB and Type IIIB. And finally, even with the
addition of sprinkler systems, the tabular area is 59,375 square feet per floor
for each of the two types of construction.
53
Sprinkler Increase
NONCOMBUSTIBLE
OCCUPANCY
A-2
B
M
COMBUSTIBLE
TYPE II
A
TYPE II
B
TYPE III
A
TYPE III
B
TYPE V
A
TYPE V
B
HEIGHT
S/Ft
3/65
4/85
2/55
3/75
3/65
4/85
2/55
3/75
2/50
3/70
1/40
2/60
AREA
15,500
27,125
73,625
9,500
16,625
45,125
14,000
24,500
66,500
9,500
16,625
45,125
11,500
20,125
54,625
6,000
10,500
28,500
HEIGHT
S/Ft
5/65
6/85
4/55
5/75
5/65
6/85
4/55
5/75
3/50
4/70
2/40
3/60
AREA
37,500
65,625
178,025
23,000
40,250
109,250
28,500
49,875
135,375
19,000
33,250
90,250
18,000
31,500
85,500
9,000
15,750
42,750
HEIGHT
S/Ft
4/65
5/85
4/55
5/75
4/65
5/85
4,55
5/75
3/50
4/70
1/40
2/60
AREA
21,500
37,625
102,125
12,500
21,875
59,375
18,500
32,375
87,875
12,500
21,875
59,375
14,000
24,500
66,500
9,000
15,750
42,750
Another interesting twist to these numbers is that Type V A - protected
wood frame construction (or 1-hr protected wood frame) is comparable to
Type II B unprotected steel, in many cases offering greater floor area. This
would permit untreated wood to be used throughout the structure, although
most assemblies within the structure would be required to be 1-hr fire
resistance rated.
54
Unlimited Area Buildings
Section 507
• Unsprinklered buildings:
– Limited to one story
– F-2 & S-2 with yards at
least 60’ in width
• Sprinklered, 1 story:
– A-4, B, F, M & S with
yards at least 60’
• Exceptions for some
uses
• Sprinklered, 2 story:
– B, F, M, & S
Having said all that, let's talk about circumstances in which the area of the
building is permitted to be unlimited. These provisions reflect the text of the
2000 edition of the IBC. Other than the change made to the 2003 edition,
these provisions are not dependent on type of construction. The change in
the 2003 edition, however, does not permit Type V construction for 2-story,
sprinklered, unlimited area buildings.
55
Reduced Open Space
Section 507.4
• 60 feet may be reduced
to 40 feet if
– Not more than 75% of
building perimeter
– Exterior walls at 40 feet
must be 3-hr rated
– Opening must be 3-hr
rated
And there are situations in which open space around the building of an
unlimited floor area building may be reduced. For example, Section 507.4
permits the reduction of the 60’ open perimeter to be reduced to 40’ if:
•Not more than 75% of the building perimeter is reduced,
•The exterior walls at 40 feet are 3-hr fire resistance rated, and
•The openings are protected with 3-hr fire resistance rated fire protectives.
56
Fire Resistance
Let’s move on to the second portion of our program: fire resistance as
addressed in the IBC. The IBC requires minimum fire resistance ratings for
various elements of the building: structural frame, walls, partitions,
floor/ceiling assemblies, etc.
57
Fire Resistance Ratings & Tests
Section 703
• The fire resistance
rating of buildings shall
be determined in
accordance with
–
–
–
–
ASTM E119
Tabular methods
Calculated methods
Designs documented in
approved sources
The IBC requires the fire resistance of various assemblies to be determined
by one of several methods. Section 703 specifies those methods:
•ASTM E119 testing
•Tabular methods
•Calculated methods
•Designs documented in approved sources
58
Fire Resistance Ratings & Tests
Methods for determining fire resistance
• By tests (ASTM E119)
• Tabular
• Calculated
• Documented sources
First let’s talk about testing. Methods for determining fire resistance by using
ASTM E 119.
59
ASTM E119
ASTM E119 is the test for determining the fire resistance of an assembly
and it is cited specifically in the IBC. Under the formalized test, an assembly
is subjected to a standardized fire until failure, which occurs when one of the
following things happen:
•a burn-through of the assembly,
•structural failure of the assembly, or
•temperature increase on the unexposed side of the assembly beyond a
specified level.
The rating of the assembly is determined by its time to failure using one of
those criteria.
60
Fire Resistance Ratings & Tests
• Published by AF&PA
• Downloadable from
awc.org
• ASTM E119 tests
AF&PA publishes a document which contains various assemblies tested
according to ASTM E119. The current version includes some newly tested
assemblies, including some tested at 100%, or fully loaded ,capacity. This is
Design for Code Acceptance 3 (DCA 3).
61
Fire Resistance Ratings & Tests
Methods for determining fire resistance
• By tests (ASTM E119)
• Tabular
–
–
–
–
IBC Table 719.1(1): Various structural members
IBC Table 719.1(2): Walls & partitions
IBC Table 719. 1(3): Floors & roofs
Reflects tested assemblies
• Calculated
• Documented sources
The second method for determining fire resistance in the IBC is the tabular
method. The Table - 719.1(1) for structural members, 719.1(2) for walls and
partitions, and 719.1(3) for floors and roofs - appears in the IBC. This is
carried over from the Uniform Building Code. These assemblies are tested
assemblies that have been “bundled” together to make them more
accessible to code users.
62
Fire Resistance Ratings & Tests
Methods for determining fire resistance
• By tests (ASTM E119)
• Tabular
• Calculated
• Documented sources
Another method for determining fire resistance is the calculated fire
resistance method. This does not require testing.
63
Fire Resistance Ratings & Tests
One of the drawbacks to using the test method, ASTM E119, is that it is very
expensive and time consuming. And if the assembly fails to achieve the
intended ratings, the process must be repeated, resulting in additional costs
and time.
64
Fire Resistance Ratings & Tests
Calculated fire resistance
• Developed by Nat’l Research Center, Canada
– Review of more than 200 tests
– Research on fire behavior of individual materials
when combined
• Methodology recognized by IBC Section 721
• For new & existing assemblies
• Published in ASCE/SFPE 29-99
In IBC Section 721, the code provides a method for calculating fire
resistance of assemblies. The calculated fire resistance method was
developed by the National Research Center, Canada based upon a review
of more than 200 tests, and research on fire behavior of individual materials
when combined with one another. The methodology is recognized in the IBC
in Section 721. It’s useful for both new and, more importantly, existing
assemblies, and it’s published as a consensus standard by ASCE/SFPE 291999.
65
Fire Resistance Ratings & Tests
Calculated fire resistance
• Published by AF&PA
• Downloadable on awc.org
• Repeats much of what’s in
IBC but has other material
Further, calculated fire resistance is discussed in a document published by
AF&PA. This document provides the wood-related methodology in the IBC,
as well as general information beyond what the code addresses. Design for
Code Acceptance No. 4, calculated fire resistance.
66
Fire Resistance Ratings & Tests
Calculated fire resistance
• Time assigned to protective membrane
– Membrane assumed on exposed side
– Based on ability to stay in place during fire tests
– Not to be confused with finish rating
• Time assigned to studs and joists
– Based on time-to-failure after failure of protective
membrane
• Code limit of 60 minutes
Here’s a summary of the methodology. It’s important to note that the code
limits its application to fire resistance ratings of 60 minutes or less. The
summary includes:
•Time assigned to protective membranes
•Membrane assumed on exposed side
•Based on ability to stay in place during fire tests
•Not to be confused with finish rating
•Time assigned to studs and joists
•Based on a time-to-failure after failure of protective membrane
•Code limits application of this method to fire resistance ratings of 60
minutes or less
67
Fire Resistance Ratings & Tests
Calculated fire resistance:
Time assigned to protective membranes
Description of Finish
3/8” Douglas-fir plywood, phenolic bonded
1/2” Douglas-fir plywood, phenolic bonded
5/8” Douglas-fir plywood, phenolic bonded
3/8” Gypsum board
1/2” Gypsum board
5/8” Gypsum board
1/2 “ Type X gypsum board
5/8” Type X gypsum board
Double 3/8” gypsum board
1/2” + 3/8” gypsum board
Double 1/2” gypsum board
Time
(Minutes)
5
10
15
10
15
20
25
40
25
35
40
The table from DCA 4, shown above, assigned various materials commonly
used as protective membranes to time in minutes. For example, ½” Douglasfir plywood, phenolic bonded is assigned a time of 10 minutes. 5/8” Type X
gypsum board is assigned a time of 40 minutes, whereas, ½” Type X
gypsum board is assigned a time of 25 minutes.
68
Fire Resistance Ratings & Tests
Calculated fire resistance:
Time assigned for additional protection
Description of Insulation
Rockwool or slag mineral wool batts
weighing not less than ¼ lb./sq. ft. of
wall surface
In non-bearing walls: Glass fiber batts
weighing not less than ¼ lb./sq. ft. of
wall surface
Time
(Min.)
15
5
The addition of insulation will only add protection in walls. And, if you note,
for fiberglass batts that additional protection is limited to and applies only to
non-bearing walls. Whereas, mineral wool batts may be used to increase the
time for bearing as well as non-bearing walls.
69
Fire Resistance Ratings & Tests
Calculated fire resistance:
Interior Wall
2” x 4” Stud
5/8” Type X Gyp Bd
5/8” Gyp Bd
16”
Here’s how the methodology works. This example is an interior wall with
Type “X” gypsum board on one side and a double layer of regular gypsum
board on the other side.
70
Fire Resistance Ratings & Tests
Calculated fire resistance:
Interior Wall
2” x 4” Stud
Exposure from
this side
5/8” Type X Gyp Bd
5/8” Gyp Bd
16”
MATERIALS
5/8” Type X Gypsum Board
Wood Studs (16” o.c.)
Total Rating
TIME
40
20
60
From the table, we note that 5/8” Type X gypsum board is assigned a time of
40 minutes. We also note wood studs, spaced 16” o.c., is assigned a time of
20 minutes. The total time assigned to this assembly, exposed from the 5/8”
Type X gypsum board side, is 60 minutes or 1-hour.
Being an interior wall, exposure is calculated from both sides. Here we
calculate from the side with a single layer of Type “X” gypsum board. The
rating calculates to be 60 minutes. From the table we see 5/8” Type X
gypsum board is assigned a time of 40 minutes. Wood studs, 16” o.c. are
assigned a time of 20 minutes, for a total fire resistance rating assigned of
60 minutes. The reason the double layer of regular gyp board isn’t
considered in this is that the exposed-side is the gypsum Type X side, and
the studs are critical elements. If they both fail, the 2 layers of gypsum on the
unexposed side offer no protection.
71
Fire Resistance Ratings & Tests
Calculated fire resistance:
Interior Wall
2” x 4” Stud
5/8” Type X Gyp Bd
5/8” Gyp Bd
Exposure from
this side
16”
MATERIALS
5/8” Gypsum Board
5/8” Gypsum Board
Wood Studs (16” o.c.)
Total Rating
TIME
20
20
20
60
Now, calculating exposure from the other side, we use the values for 5/8”
regular gypsum. We see that 5/8” regular gypsum board is assigned a time
of 20 minutes. With 2 layers, the assigned time is 40 minutes. And, wood
studs 16” o.c. are assigned a time of 20 minutes. So, the total fire resistance
rating exposure from this side is 60 minutes. This assembly is, therefore,
considered to be a 1-hour fire resistance rated assembly.
72
Fire Resistance Ratings & Tests
Calculated fire resistance:
Another method of calculating fire resistance is the methodology for
assigning 1-hour fire resistance to exposed heavy timber beams and
columns.
73
Fire Resistance Ratings & Tests
Calculated fire resistance: exposed members
• Originally published by AF&PA as an evaluation
report
• Methodology recognized by IBC Section 721
• Recently published in ASCE/SFPE 29-99
This methodology was first introduced into the codes as a National
Evaluation Report (NER), but it has eventually moved into the body of the
code. And, it has subsequently been published as a consensus standard
ASCE/SFPE 29-1999.
74
Fire Resistance Ratings & Tests
Calculated Fire Resistance
Exposed Heavy Timber Members
Heated
zone
D
Charred
wood
W
The essential concept in this methodology is when wood of a sufficient size
is exposed to fire there will be three zones in the wood member. The core of
the member will be unaffected by the fire and will retain its strength. There
will be a heated zone in which some of its strength will be reduced. And on
the exterior of the member, there will be a char layer, which at some point in
the fire, will provide insulation to the rest of the member.
Simply stated, the concept is to design “sacrificial wood” into the member so
that when the member is exposed to fire it will retain sufficient strength to
hold its loads.
75
Fire Resistance Ratings & Tests
Calculated fire resistance: exposed members
• Based on
– Depth and width of beam/column
– Load factor
• Unsupported length/span
• End condition – fixed or free
– Ratio of allowed load to actual
• Different process for exposure on 3 or 4 sides
The detailed methodology is too complex to go into here. However, as you
might expect, the width and depth of the member comes into play. The load
factor that is used is based upon the unsupported length or span of the
member as well as the end condition of the member. And as you might
expect, because the degrees of exposure are different, the process is
somewhat different for members which are exposed on three sides
compared to those which are exposed on four sides.
76
Fire Resistance Ratings & Tests
• This document is
downloadable from
awc.org
• Contains code
information but also
added material
• Suggested fastener
protection
Fire resistance ratings using Design for Code Acceptance No. 2. AF&PA
provides this document online at awc.org. It’s informative because it gives
information on what you’ll find in the code with regard to fire resistance
ratings.
77
Fire Resistance Ratings & Tests
Development of methodology
Calculations vs. experiments
Detailed design procedures
Application guidelines
Examples
Design aids
Downloadable from AWC.org
TR 10: Calculating Fire
Resistance of
Exposed Wood Members
American Wood Council
•
•
•
•
•
•
•
American
Forest &
Paper
Association
American Wood Council
If you’re really interested in this methodology, Technical Report No. 10
(TR10) provides a great deal of information. It includes:
•Calculations and experiments
•Detailed design procedures
•Application guidelines
•Examples
•Design aids
78
Fire Resistance Ratings & Tests
Methods for determining fire resistance
• By tests (ASTM E119)
• Tabular
• Calculated
• Documented sources
Lastly, determining fire resistance rating recognized in the IBC by what it
refers to as “documented sources.”
79
Fire Resistance Ratings & Tests
This would include:
•The Underwriters Laboratory Fire Resistance Directory
•The Gypsum Association Fire Resistance Directory, and
•Other directories, such as those published by Intertek Testing Services
80
Flame Spread
Finally, let’s talk about the subject of flame spread as it’s addressed in the
code and see how wood fits into those provisions. It’s important to first
talk about the difference between flame spread and fire resistance. Fire
resistance, as we’ve seen, concerns the resistance of a material or
assembly of materials to:
•
Resist fire damage to the extent that it compromises the structural
stability of the assembly, or
•
That it permits burn-through for the passage of fire and smoke, or
•
The transfer of heat such that it might ignite combustible materials on the
unexposed side.
Flame spread concerns the length of time required for fire on the surface of
the material to travel across the material.
81
Flame Spread
Here is a copy of IBC Table 803.5 (from the 2003 edition). Notice, that the
format of the table has the reader match a particular occupancy group with
sprinklered or unsprinklered areas of the building. The body of the table,
under those columns then, lists the flame spread requirement as a
classification A, B, or C.
82
Flame Spread
• Class A
– Flame spread 0 – 25, smoke developed 0 - 450
• Class B
– Flame spread 26 – 75, smoke developed 0 - 450
• Class C
– Flame spread 76 – 200, smoke developed 0 - 450
Class A
Flame spread 0 – 25
Class B
Flame spread 26 – 75
Class C
Flame spread 76 – 200
For all of these classifications, the smoke developed rating must be 0-450.
In some of the Legacy Codes, a similar table was used, but the designations
used were Class I, Class II, and Class III.
83
Flame Spread – ASTM E84
Flame spread is determined by the use of ASTM E-84 tests, sometimes
referred to as the Stiener Tunnel test. In this procedure, the material to be
tested is mounted in the ceiling of the tunnel. In one end of tunnel, the
material is exposed to a standardized flame with standardized air flow across
the surface of the material. The distance which the flame spreads over a
period of time determines the flame spread rating. While this test gives an
indication of the performance of the materials exposed to the same
conditions, it is not intended to be a reflection of performance of the material
in a real fire exposure. It is merely a relative categorization of materials.
84
Flame Spread
Flame spread of wood products
CLASS A
0 - 25
Fire retardant treated wood
CLASS B
26 - 75
Redwood
Cedar
CLASS C
76 - 200
Most other species
Softwood plywood
Hardwood plywood
Particleboard
Here’s how wood products are classified. Most wood products fall, as you
can see, under Class C: 76-200 – softwood plywood, hardwood plywood,
most species of wood. Redwood and some Cedars fall under Class B: 2675. And, fire retardant treated wood is Class A: 0-25.
85
Flame Spread
• Published by AF&PA
• Downloadable from
www.awc.org
Finally, Design for Code Acceptance No. 1, published by AF&PA, contains
information on flame spread rating which is sometimes difficult to find
elsewhere.
86
Questions?
• www.awc.org
– Online eCourses
– FAQ’s
• HelpDesk
– AWCinfo@afandpa.org
– (202) 463-4713 or (800) 292-2372
• Comments
– AWC_education@afandpa.org
This concludes this approved
continuing education program.
Last slide
87