STF20070014 App letter dated 7-2-07.pdf'grace
May 14, 2007
To the City of Ednonds
Building Department
Hand Delivered
Subject: Alternate design review request 1 Old Milltown / heavy timber columns
To whom it may concern
We are requesting that the city review and allow the use of 8x8 Glu Lanacolunuas
for the primary structural elements to be used as indicated on the Structural Plans
for the project. We are malting this request to use the referenced heavy timber
columns as allowed in many municipalities around the country where preservation
of historic buildings is paramount. -For instance the Seattle IBC interpretation
1602.5 is as follows:
Type VA building may include exposed heavy -timber construction for colurrrns,
beams, girders, arches, trusses, floors and roof decks except for fire resistive
construction required by section 707 and chapters 5 and 10.
This suggested interpretation is supported in a variety of sections as noted below
as it relates to the fire resistivity of the proposed element. The structural efficacy
of the column is established separately as part of the now approved structural
design.
Tables 503 and 601 clearly establish the code equivalency beth,,,ecn our
proposed Heavy Timber usage at the colunuis only and the levels of
protection attained for a type 5A building. This is deduced from the
obvious indication that. all of the heavy timber building heights and areas
are in excess of those allowed in the type 5A building across all
occupancy group types. This interpretation is supported in the excerpted
section from the IBC conunentary Vol 1 on the 2003 IBC... section 602.4
States in the cozaunentary:
o "The interior elements are required, to be unprotected because of
the massive element sizes and the requirements that there not be
any concealed spaces, such as soffits, plenums or suspended
ceilings.
(Where our proposed colunurs enter such a space, they are
entering into a rated assembly, the penetration of which
shall be properly fire -caulked, should a suspended ceiling
be placed as part of the tenant wank, the wood column will
1927 Post Alley Seattle, WA 98701 206957-9800
f 206-682-3159
Www..gracearcliltectsplic.coilI
be appropriately wrapped with 1 hour protective
construction above the ceiling.)
o ...an examination of table 503 indicates that the allowable height
and areas for type IV construction is greater than that permitted for
buildings to type IIb construction. This distinction is based on
testing that demonstrated that HT structural members perform
better structurally under fire conditions than comparable
unprotected steel members because of charring, which insulates the
wood mass.
(We maintain that this is also the case for the relationship
to Type VA structural members as stated earlier and we are
proposing that similar conclusion applies.)
Section 602.4.1 requiring an miniiilum. 8" dimension for Columns carrying
floor and roof loads as being compliant with the requirements of HT
construction that will meet the equivalent fire protection requirements.
The Commentary goes on to establish the relationship between the
Nominal and actual dimensional requirement of the HT structural
laminated column. We are well in excess of these minium requirements
as the specific requirement is for a 6x8" nominal column when supporting
floor, roof and ceiling loads. This equates to a 5-118" x 6-114"
dimensional column and we are providing glu-lam columns in 8-114" x 8-
114" in actual dimension. Where these items are part of a required exit
corridor, they will be protected as required by type VA construction
requirements.
fearuline, I hope that these additional elaborations will assist you iii making your
ruling with eonfrdenee that this is a well established and viable alternative design
methodology and one that will not only keep our building safe, but will euhanee
the historic character of the remodeled building for many generations to come.
Thanks for your consideration.
4435 ARCI�IERC
s
RALPH W. At I EN
I.PSTATE OF WASHINGTON
Ralph W. Allen
Principal
1927 Post Alley Seattle, WA 98109 p 201-957-9800
f 206-.682-3159
www. gracearchi tectspllc.Coln
IW7
TYPES OF CONSTRUCTION
nal in width, set on edge close together and laid as required
for floors. Other types of decking shall be permitted to be
used if providing equivalent fire resistance and structural
properties.
602.4.6 Partitions. Partitions shall Uo of solid wood con-
struction formed by not less than two layers of 1 -inch (25
nun) matched boards orlarninated construction 4 inches (102
min) thick, or of 1 -hour fire -resistance -rated construction.
602.4.7 Exterior structural members. Where a horizontal
separation of 20 feet (6096 ITmi) or more is prodded, wood
columns and arches conforming to heavy timber sizes shall
be permitted to be used externally.
602.5 Type V. Type V construction is that type of construction
in which the structural elements, exterior walls and interior
walls are of any materials permitted by this code.
Interpretation I602.5: ypeVA
buildings may include
ex-
posed heavy-firnber const •actio
r umns 1 )eaBis,
gird-
ers, arches. trusses floors and
roof decks except
for
fire-regigiye construcdon-l=uired
7 and
Chap-
teus 5 and 10.
SECTION 603
COMBUSTIBLE MATERIAL IN TYPE I
AND II CONSTRUCTION
603.1 AIlowable materials. Combustible materials shall be
permitted in buildings of Type Ior II construction in thefollow-
ing applications and in accordance with Sections 603.1.1
through 603.1.3:
1. Fire -retardant -treated wood shall be permitted in:
1.1. Nonbearing partitions where the required fire -re-
sistance rating is 2 hours: or less.
1.2. Nonbearin; exterior walls where no fire rating is
required.
1.3. Roof construction as permitted in Table 601,
Note c, Item 3.
2. Ther n-ial and acoustical insulation, other than foam plas-
tics, having a flame spread index of not more than 25..
Exceptions:
1. Insulation placed between two layers of
noncombustible materials without an inter-
vening airspace shall be. allowed to have a
flame spread index of not more than 100.
2. Insulation installed between a finished floor
and solid decking without inteivening air-
space shall be allowed to have a flame spread
index of not more than 200.
3. Foam plastics in accordance with Chapter 26.
4. Roof coverings that have an A, B or C classification.
5. interior floor finish and interior finish, trim and mill-
work such as doors, door frames, window sashes and
frames.
6. Where not installed over 15 feet (4572 mm) above
grade, show windows, nailing or furring strips, wooden
104
bulkheads below show windows, their frames, aprons
and shod' cases.
7. Finished flooring applied directly to the floor slab or to
wood sleepers that are firestopped in accordance with
Section 717.2.7.
S. Partitions dividing portions of stores, offices or similar
places occupied by one tenant only and which do not
establish a corridor serving an occupant load of 30 or
more shall be permittecl to be constructed of
fire -retardant -treated wood, 1 -hour fire -resistance -
rated construction or of wood panels or similar light
conscLuction up to 6 feet (1829 mm) in height.
9. Platforms as permitted in Section 410. 40
10. Combustible exterior wall coverings, balconies, bay
or oriel windows, or similar appendages in accor-
dance with Chapter 14.
11. Blocking such as for handrails, millwork, cabinets, and
window and door frames.
12. Light -transmitting plastics as permitted by Chapter 26.
13. Mastics and caulking materials applied to provide flexi-
ble seals between components of exterior wall construc-
tion.
14. Exterior plastic veneer installed in accordance with
Section 2605.2.
15. Nailing or furring strips as permitted by Section 803.4.
16. Heavy timber as permitted by Note c, Item 2, to Table
601 and Sections 602.4.7 and 1406.3.
17. Aggregates, component materials and admixtures as
permitted by Section 703.2.2.
19. Sprayed cementitious and mineral fiber fire -resistance -
rated materials installed to comply with Section 1704.11.
19. Materials used to protect penetrations in fire -resistance -
rated assemblies in accordance with Section 712.
20. Materials used to protect joints in fire -resistance -rated
assemblies in accordance with Section 713.
21. Materials allowed in the concealed spaces of buildings
of Type I-ana II construction in accordance with Sec-
tion 717.5.
22. Materials exposed within plenums complying with'
Section 602 of the International Mechanical Code.
23. Stairways withill in 'dual dwe i - t i G d s 'waw
s vi b a sit o tenai s a ma ofire-iiptatdauL
at di n or av - e stia 'on. tI r ha
Group c u cies. t 1 stairways shall llotsvemas
- a required m!,-,lns.Qf egress,.
603.1.1 Ducts. The use of nonmetallic ducts shall be permit-
ted when installed in accordance with the limitations of the
International Mechanical Code.
603.1 .2 Piping. The use of combustible piping materials
shall be permitted when installed in accordance with the
limitations of the International Mechanical Code and the
Ullifnrnr Plr.rrnbiirg Code.
603.1.3 EIectrical. The use of electrical wiring methods
with combustible insulation, tubing, raceways and related
components shall be permitted when installed in accordance
with the limitations of the IGE Seattle Electrical Code.
2403 SEATTLE BUILDING CODE
GENERAL BUILDING HEIGHTS AND AREAS
TABLE 503
ALLOWABLE HEIGHT AND BUILDING AREAS
y -
Height
limitations shown as stories and
feet above grade plane.
Area limitations
as determined by the definition of "Area, building,"
per fl
-
TYPE OF CONSTRUCTION
i
TYPE
1
TYPE 11
TYPE 111
TYPE IV
TY EV
B
ATB5
A
B
HTGROUP
ffAL
Hat(5}
160
65
55
55
65
50.
40
-
A 1
S
UL
UL
5
UL
3
15500
2
8,SD0
3
14,040
2
8,500
3
}5,400
2
11,500
1
5,500
A-2
A
S
UL
I1
UL
3
15,500
2
9,500
3
14,DOD
2
9,500
3
15,00('
2
11500
I
6,000
A
UL
2
1
A-3
UL
UL
3
15 500
2
9,500
3
14,000
2
9,504
3
15,400
11,500
6,OOD
A-4
S
U�
CFL
1€
UL
3
15,500
2
9,500
g
€4,004
2
9,500
3
15,000
�
11500
I
6,000
A
S
UL
UL
UL
UL
UL
UL
UL
' UL
UL
UL
�
UL
UL
A 5
A
UL
UL
UL
UL
UL
UL
A
[UILL..
11
UL
5
37,500
23600 ''
5
28,50D
4
19,000
5
36,000
;
IS,000
3
9,000 '
5
UL
3
26,504
2
14,540
3
23.500
?
14,506
3
25,5(0
€
]3,500
1
9,5011
L- S
A
UL
4
2
3
2
4
2
1
F-1
S
UL
UL
]l
UL
25,000
15,500
19,000
12.040
33,500
14,400
5,500
F-2
A
S
UL
11
UL
5
37,500
3
23,000
4
28,540
3
18,OOD
5
50,500
3
21,000
2
13,000
A
UL
1
I
NP
H-1
S
A
l
21.000
1
16,500
I
11,000
]
7,000
I
9,500
I
7,000
10,504
7,500
NP
H-2
S
A
UL
21,000
3
1650011,000
2
1
7,000
2
9500
1
71000
2
10,500
1
7,500
]
3,000
H-3
A
UL
5
I 60,000
4
26.500
2
1400(
4
17,500
2
13,004
4
25500
2
10,000
l
5,006
II- 4
S
UL.
UL
UL
37500
17 500
28,500
3
17,50D
5
31,000
3
15,000
2
6,504
1.1-5
UL
UL
37,500
3
23,000
3
28.503
3
]9,000
3
36,006
3
lSOUO
?
4,000
1-1
A
S
UL
UL
9
55,(00
}
19,00{5 fff
3
10,000
4
11,500
3
10.000
4
18,000
3
]0,500
2
4,540
A
,
1
NP
I
l
NP
}4
I--7
1
5
UL
UL
UL
2-
15,004
1
11,400
12,000
�P
12,OQ0
9,500
VP
A
2
2
1
]3
5
UL
UL
4
UL
2
15,009
I
10,000
2
10,504 -
1
` 7.544
12,000
7,500
S,OOD
1 4A
A
g
UL
UL
5
6,0,540
3
26,500
13,000
23500
13000
25,500
I
18,500
I
9,000
S
UL
11
UL
4
21500
4 .
12.50(
4
18,500
4
12,500
4 -
20,500
3
14,400
1
9,000
A
S
UL
UTI.,
it
UL
4
24,000
4
16,000
4
24,006
4
16,000
4 �
20,500
34
12,(140
2
7,000
A
UL
4
4
4
4
34
2
R_2n
S
UL
UL
11
2} g 4
16,000
24,000
16,OOD
20500
12,000
7,000
A
4
4
4
4
4
3L
R-3-`
S
A
UL
UL
11
UL
UL
UL
UL
UL
UL
UL
UL
R 4
S
UL
ULUI.
11
2q OOD
4
16,000
4
24.000
4
16,(00
4
20500
3
12,(00
2
7,000
A
3
4
3
I
S-1
S
CIL
UL
i I
45.000
26,000
17,500
26 004
17.500
25,500
14,000
9,000
S-2� `A
A
S
UL
UL
l l
79,OOD
5
39,006
4
26,000
4 I
39,D00
4
26,000
5
35,506
4
2t,a64
2
13,5(0
Uc
S
UL
5
35,500
4
19,000
2
3,500
3
14,004
2
$500
4
18,000
2
9,400
l
5,500
A
UL
For SI; I foot
30=4.8 min, I'square foot = 0.0929 m'.
UL =Unlimited, NIP =-Not
penuitted.
a, As app[icable
it, Section
101.2.
open .lri,l
b. Por P
P
u0, structures
see Section
406.3.
c. For private garages, see
Section 406.1.
97
2003 SEATTLE BUILDING CODE
TYPES OF CONSTRUCTION
TABLE 601
FIRE -RESISTANCE RATING REQUIREMENTS FOR BUILDING ELEMENTS (hours)
TYPE I TYPE H TYPE III TYPE. IV TYKE V
d $
BUILDING ELEMENT A B Ad B Ad l3 BT
Structural frame'
Including colulmis, girders, trusses 3b 2s 1 0 1 0 HT 1 0
I3earing walls 2 2 i 0
> xteriorr 3 2 1 0
Interior 3b 2" 1 0 1 0 1LHT 1 0
Nonbearing walls and partitions L
Exterior See Table 602
Nonbearing walls and partitions 0 0 0 0 0 0 See Section 602.4.6 0 0
Interiors
Floor construction 2 2 1 0 1 0 HT 1 0
Including supporting beams and joists
Roof construction I,/,c I` I= 0` 0 HT 1` 0
Including supporting beams ant] joists
For SI: 1 foot = 304.8 mm.
a. The structural frame shall be considered to be the columns and the girders, beams, trusses and spandrels having direct connections to the columns and bracing
members designed to carry gravity loads. The members of floor or roof panels+'hick have no connection to the columns shall be considered secondary members
and not a part of the structural frame.
infer ret. ion 1601: Bririnoi emhesth, rov'deve cals7hilit'shallh consjdered Part of the sialcalralframewhetlerartnthevca y a_Mvity1 s
b. Roof supports: Fire -resistance ratin-es of structural frame and bearing galls are permitted to.be reduced by 1 hour where supporting a roof only.
c. L F-xcepl in Factory -Industrial (F -I), Hazardous (H), U'lereantile (NI) and Moderate -Hazard Storage (S-1) occupancies, fire protection of structural members
shall not be required, including protection of roof framing and decking where every part of the roof construction is 20 feetor more above any floor inunediately
below. Fire -retardant -treated wood members shall be allowed to be used for such unprotected members.
2. In all occupancies, heavy timber shall be allowed where a I -hour or less fire -resistance rating is required.
3. In Type I and II construction, fine -retardant -treated wood shall be allowed in buildings including girders and trusses as part of the roof construction when t€te
building is:
I. Two stories or less in height;
ii. Type II construction over nvo stories; or.
iii. Type 1 construction over owo stories and the vertical distance from the upper floor to tile roof is 20 feet or more.
d. An approved automatic sprinkler system in accordance with Section 903.3.1.1 shall be allowed to be substituted for I -hour lire -resistance -rated construction, pro-
vided such system is not otherwise required by other provisions of the code or used for art allowable area increase in accordance with Section 506.3 or an allowable
height increase in accordance with Section 504.2. The 1 -hour substitution for the fire resistance of exterior trolls shall not be permitted.
Ris WIr-611160D bbill not
be __ in building—.e.r.,,...,.r.l:,,o hn.CPrlinn 1(€18.2e%('� np d�L4I. _ _
e. Not less than the fire -resistance rating required by other sections of this code.
f. Not less than the fire -resistance rating based on fire separation distance (see Table 602).
105
CHAPTER 6
SECTION 601
GENERAL
601.1 Scope. The provisions of this chapter shall control the
classification of buildings as to type of construction.
SECTION 602
CONSTRUCTION CLASSIFICATION
602.1 General. Buildings and structures erected or to be
erected, altered or extended in height or area shall be classified
in one of the five construction types defined in Sections 602.2
through 602.5. The building elements shall have a
fire -resistance rating not less than that specified in Table 601
and exterior walls shall have a fire -resistance rating not less
than that specified in Table 602.
6021.1 Minimum requirements. A building or portion
thereof shall not be required to conform to the details of a
type of construction higher than that type, which meets the
minimum requirements based on occupancy even though
.certain features of such a building actually conform to a
higher type of construction.
602.x. `Types land II. Type I and II construction are those types
of construction in which the building elements listed in Table
601 are of noncombustible materials.
602.3 Type III. Type III construction is that type of construc-
tion in which the exterior walls are of noncombustible materi-
als and the interior building elements are of ally material
permitted by this code. Fire -retardant -treated wood framing
complying with Section 2303.2 shall be permitted within exte-
rior wall assemblies of a 2 -hour rating or less.
Intexln-etation1602.3:
Type IIIA buildings irnav include ex-
posed heavy timber construction
for columns- beams. >7ird-
_
rs, arches, tr es s floors
and f decks except o1`
fire resistive constructirni
re4liii-ed by Section 707 and
C'haptel:s 5 and 1 Cl
602.4 Type Il'. Type IV construction (Heavy Timber, HT) is
that type of construction in which the exterior walls are of
noncombustible materials and the interior building elements
are of solid or laminated wood without concealed spaces. The
details of 7),pe IV construction shall comply with the provi-
sions of this section. Fire -retardant -treated wood framing com-
plying with Section 2303.2 shall be perniitted within exterior
wall assemblies with a 2 -hour rating or less.
602.4.1 Columns. Wood columns shall be sawn or glued
laminated and shall not be less than 8 inches (203 nun),
nominal, in any dimension where supporting floor loads and
not less than 6 inches (152 mm) nominal in width and not
less than 8 inches'(203 mm) nominal in depth where sup-
porting roof and ceiling loads only. Colunms. shall be con-
tinuous or superimposed and connected in in approved
manner. 4
2003 SEATTLE BUILDING CODE . .
602.4.2 Floor framing. Wood beams and girders shall be of
sawn or glued -laminated timber and shall be not less than 6
inches (152 mm) nominal in width and not less than 10
inches (254 rain) nominal in depth. Framed sawn or
glued -laminated timber arches, which spring from thefloor
line and support floor loads, shall be not less than S inches
(203 linin) nominal in any dimension. Framed timber trusses
supporting floor loads shall have members of not less than 8
inches (203 mm) nominal in any dimension.
602.4.3 Roof frau-drag. Wood -frame or glued -laminated
arches for roof construction, which spring from the. floor
line or from grade and do not support floor loads, shall have
members not less than 6 inches (152 mm) nominal in width
and have less than 8 inches (203 niln) nominal in depth for
the lower half of the height and not less than 6 inches (152
ram) nominal in depth for the upper half. Framed or glucd-
laminated arches for roof construction that spring from the
top of walls or wall abutinents, fraEned timber trusses and
other roof framing, which do not support floor loads, shall
have members not less than 4 inches (102 mm) nominal in
width and not less than 6 inches (152 man) nominal in depth.
Spaced members shall be permitted to be composed of two
or more pieces not less than 3 inches (76 nun) nominal in
thickness where blocked solidly throughout their interven-
ing spaces or where spaces are tightly closed by a continu-
ous wood cover plate of not less than 2 inches (51 nun)
nominal in thickness secured to the underside of the mernt-
bers. Splice plates shall be not less than 3 inches (76 nun)
nominal in thickness. Where protected by approved auto-
matic sprinklers under the roof deck, framing members
shall be not less than 3 inches (76 mm) nominal in width.
602.4.4 Floors. Floors shall be without concealed spaces.
Wood floors Shall be of sawn or glued -laminated planks,
splined or tongue -and -groove, of not Iess than 3 inches (76
nim) nominal. in thickness covered with 1 -inch (25 nun)
nominal dimension tong€ie-and-groove flooring, laid cross-
wise or diagonally, or 0.5 -inch (12.7 min) particleboard or
planks not less than 4 inches (102 nnnn) nominal in width set
on edge close together and well spiked and covered with
1 -inch (25 num) nominal dimension flooring or 151,E -inch
(12 inm) wood structural panel or 0.5 -inch (12.7 man)
particleboard. The lumber shall be laid so that no continu-.
ous line of joints will occur except at points of support.
Floors shall not extend closer than 0.5 inch (12.7 urn) to
walls. Such 0.5 -inch (12.7 nim) space shall be covered by a
molding fastened to the wall and so arranged that it will not
obstruct the swelling or shrinkage movements of the floor.
Corbeling of masonry walls under the floor shall be permit-
ted to be used in place of molding:
602.4.5 Roofs. Roofs shall be without concealed spaces and
wood roof decks shall be sawn or glued laminated, splined
or ton'gue-and-groove plank, not less than 2 inches (51 nnili)
thick, 111$ -inch -thick (32 ram) wood structural: panel (exte-
rior gIue), or of planks not less than 3 i nclics (76 mm) nonni-
103 li
-fypES OF CONSTRUCTION
assemblies. For example, the required rating for struc-
tural frame members in Type IA construction is 3 hours,
for Type IB is 2 hours, for Type IIA is 1 hour and for Type
1113 is 0 hours. The required fire -resistance ratings of
structural elements range from zero for Type IIB con-
struction to 3 hours for most of the elements of Type IA
construction. Often, the fire -resistance ratings required
by Tables 601 and 602 for structural elements are
achieved by "fireproofing" structural members. Fire-
proofing is typically the process of creating a fire -resis-
tance -rated assembly that incorporates the structural
member by encapsulating it, either by boxing it in or by
spraying on a coating to achieve the required fire -resis-
tance ratings. It should be noted that when a protective
covering is used to provide the fire -resistance rating, it
must be a noncombustible material, except as indicated
in Section 603.1, Item 18 and in Section 703.2.2.
Fire -retardant -treated wood (FRTW), although combus-
tible, is permitted in limited uses in buildings of Type I
and II construction (see Section 603 and Table 601,
Note C). While FRTW is permitted in certain applica-
tions in buildings of Type I and ll construction, it is not
assumed to be fire -resistance rated, and generally does
not afford any higher fire -resistance rating than un-
treated wood material.
602.3 Type III. Type III constriction is that type of construction
in which the exterior walls are of noncombustible materials and
the interior building elements are of any material permitted by
this code. lire -retardant -treated wood framing complying with
Section 2303.2 shall be permitted within exterior wall. assem-
blies of a 2 -lour rating or less.
.• Buildings of Type III construction are made with both com-
bustible and noncombustible materials. The exterior walls
are required to be noncombustible with load-bearing exte-
rior walls required to have a minimum 2 -hour fire -resis-
tance rating. Exterior nonload-bearing walls are not
required by Table 601 to have a fire -resistance rating, but
must comply with the provisions of Table 602. The •interior
elements (i.e., floors, roofs and walls) are permitted to be
of combustible materials. An example of a typical building
of Type Ill construction is a structure having its. exterior
walls constructed of concrete, masonry or. other approved
noncombustible materials, but with a wood -frame floor
and roof construction (see Figure 602.3 for an example of
Type 111 construction). Type III construction is further di-
vided into two subclassifications: Types IIIA and I1113, An
example of a building of Type IIIA construction is one in
which the interior load-bearing walls, floors, roofs [those
members that are less than 20 feet (6096 mm) to the low-
est member] and all structural members are protected to
provide a minimum 1 -hour fire -resistance rating. The
structural members of a building of Type IIIB construction
are not required to have a fire -resistance rating with the
exception of the exterior load-bearing wails.
Although FRTW sloes not meet the specifications of
the code as a noncombustible material, it is permitted
as a substitute for noncombustible materials in exterior
wall assemblies of Type III construction, While the exte-
rior walls are permitted to be either nonload bearing or
602.3 — 602.4
load bearing, the required fire -resistance rating of the
exterior wall must be no greater than 2 hours where
FRTW is used. FRTW is required to comply with the pro-
visions in Section 2303.2.
GYPSUM
WALLEOARO
W000 RAFTERS FURRED PdNLi.ING
AND TRIM d (�
CON CRE F BLOCK
%I� t
�crasura Sr�aueaARo
BRICK
- t�: •I WOOD JUST AND FLOOR
Figure 602.3
EXAMPLE OF TYPE III CONSTRUCTION
602.4 Tt ,pe IV. Type IV construction (Heavy Timber, HT) is that
type of construction in which the exterior walls are of
noncombustible materials and the interior buildin.-.elements are
of solid or laminated wood without concealed spaces. The de-
tails of Type IV construction shall comply with the provisions of
this section, Fire -retardant -treated wood framing complyin.-
with Section 2303.2 shall be permitted within exterior wall as-
semblies with a 2 -hour rating or less.
•:•This section provides the general regulations for Type
IV HT construction, HT construction requires the exte-
rior walls to be constructed of noncombustible materi-
als. The interior elements are required to be constructed
of solid or laminated wood without anyconcealed
spaces. All, of'the combustible structural elements are
permitted to be unprotected because of the massive el-
ement sizes and the requirement that there not be any
concealed spaces, Such assoffits, plenums or sus-
pended ceilings. Sections 602.4.1 through 602.4.7 pro-
vide specific requirements for the connection of
structural members and minimum dimensions. An ex-;
amination of Table 503 indicates that the allowable
height and area for Type !V construction is greater than
that permitted for buildings of Type IIB construction.
This distinction is based on testing that demonstrated
that HT structural members perform better structurally
under fire conditions than comparable unprotected steel
structural members because of charring, which insu-
lates the wood mass.
As with Type III construction, FRTW is permitted as a
substitute for noncombustible materials in exterior wall
assemblies of Type IV construction. While the exterior
walls are permitted to be either nonload bearing or load
bearing, they must have a fire -resistance rating of no
greater than 2 hours where FRTW is used in the exterior
wall, FRTW is required to comply with the provisions of
2003 INTERNATIONAL BUILDING CODE° COMMENTARY 6-3 .
602.4.1 — 602.4.3 TYPES OF CONSTRUCTION ::'-ITYPES
Section 2303.2.
It should be noted that the sizes of specified timber
members are nominal. Actual sizes for sawn timbers will
generally be'12 inch (12.7 mm) to 314 inch (19.1 mm) less
than nominal in both width and thickness as required by
the U.S. Department of Commerce Standard PS 20 -99. -
Due to requirements for additional finishing (sanding),
glued laminated sizes will be less, as shown in Figure
602.4.
Nominall
(inches)
3 1 4
f
6
S
10
12
i
( 14
16
1
Actual
(inches)
12114 31/,
51/8
6314
8314
1031q
12'14
14'14
For 51: 1 inch = 25.4 mm.
Figure 602.4
NOMINAL VERSUS ACTUAL DIMENSIONS FOR
GLUED -LAMINATED MEMBERS
.1 Columns. Wood columns shall be sawn or glued lami-
nated and shall not be less than 8 inches (203 mm), nominal, in
any dimension where supporting floor loads and not less than 6
inches (152 nein) nominal in width and not less than 8 inches
(203 min) nominal in depth where, supporting roof and ceiling
loads only. Columns shall be continuous or superimposed and
.connected in an approved manner:_ _00
.• Minimum construction requirements and dimensions for
timber columns aro provided in this section. Columns
are required to be a minimum of 8 inches (203 mm)
nominal in any dimension if they support floor loads, or a
minimum of 6 by 8 inches (152 by 203 mm) nominal if
they support a roof and ceiling. Timber columns are re-
quired to be continuous or superimposed, positioned on
or over each other, through floors for the entire height of
the building. The design engineer or architect must pro-
vide details of all column connections. As with all struc-
tural members, each column must also be adequately
fastened to other structural members in order to with-
stand the loads that will be placed upon the column.
Some typical examples include reinforced concrete or
metal caps, steel or iron column caps and timber splice
plates [see Figures 602.4.1 (1) and 602.4.1(2)].
602.4.2 Floor framing. Wood beams and girders shall be of
sawn or glued -laminated timber and shall be. not Iess than 6
inches (152 iron) nominal in width and not less than 10 inches
r mm) nominal in depth. Framed sawn or glued -laminated
`ar arches, which spring from the floor line and suppoit.floor
loads, shall be not less than 8 inches (203 n1m) nonduat is any
dimension. Framed timber trusses supporting floor loads shall
have members of not less than 8. inches (203 mm) nominal in
any dimension.
*4• Minimum construction requirements and dimensions for
floor framing are provided in this section. Girders aro
the principal horizontal structural members that support
columns or beams. Beams are the structural members
that support a floor or roof. Both girders and beams are
required to be a minimum 6 inches (152 mm) wide and
10 inches (254 mm) deep. Both framed timber trusses
supporting floor loads and framed sawn or glued lami.
nated timber arches that spring from the floor line and
support floor loads are required to be at least 8 inches
(203 mm) in any dimension.
602.4.3 Roof framing. Wood -frame or glued -laminated arches
for roof construction, which spring from the floor line or from
;rade and do not support floor loads, shall have members not
less than 6 inches (152 mm) nominal in width and have less titan
8 inches (203 mm) nominal in depth for the lower halt of the
height and not less than 6 inches (152 nun) nominal in depth for
the upper half. Framed or glued -laminated arches for roof cott-
suriction that spring from the top of walls or wall abutments,
framed timber trusses and other roof framing, which do not sup-
port floor loads, shall have members not less than 4 inches (102
mm) nominal in width and notless,than 6 inches (152 nim) nom-
inal in depth. Spaced members shall be permitted to be com-
posed of two or more pieces not less than 3 inches (76 nun)
nominal in thickness where blocked solidly throughout their in-
tervening spaces or where spaces are tightly closed by a continu-
atts wood cover plate of not less than 2 inches (51 mm) nominal
in thickness secured to the underside of the members. Splice
plates shall be not less than 3 inches (76 mm) nominal in thick-
ness. Where protected by approved automatic sprinklers under
the roof deck, framing members shall be not Iess than 3 inches
(76 mm) nominal in width.
+;• Minimum construction requirements and dimensions for
arches and other types of roof framing are provided in
this section. Other types of roof framing included in this
section.are heavy timbertrusses with spaced members.
When the members of a heavy timber truss are split and
placed on either side of a main member, such as a web
connecting a chord, each component of the web must
be 3 inches (76 mm) or more in nominal thickness. The
space between the two web members must be pro-
tected with a 2 -inch -thick (51 mm) cover plate [see Fig-
ure 602.4.3(1)], or solidly filled with blocking [see Figure
602.4.3(2)]. The size of the roof framing members is de-
pendent on the configuration used and is regulated by
this section.
If a building of Type IV construction is equipped with
approved automatic sprinklers under the roof deck, the
minimum size of the roof framing members is reduced
to 3 inches (76 mm). Roof framing members of a smaller
size will have a lower resistance to fire than the 6 -inch
by 8 -inch (152 mm by 203 mm) or 4 -inch by 6-inch.002
mm by 152 mm) members required by this section. The
tradeoff allowing smaller roof framing members when
the building is equipped with an automatic sprinkler sys-
tem is consistent with the concept of maintaining "equiv-
alent risk" for the building.