STF2007-0014 Applicant response dated 6-26-07.pdfkracAARCHITECTS PLLC
May. 1.4, 2007
, ESUB
To the City. of:Ednionds JUN 26 2007
Building Department
Hand 'Delivered
Subject: Alternate design review request./Old Milltown / heavy timber. columns
To whom.it may concern
We are requesting that the city review and allow the use of 8x8 Glu Lam columns
for the primary structural elements to be .used as indicated on the Structural Plans
for. the, .project. We ;are making 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.
I602.5 is as follows:
Type VA building 'may include exposed heavy-timber construction for columns,
beams, girders, arches, trusses, floors and roof. decks except for fare resistive
construction required by section 707 and chapters 5 and 10:
This suggested interpretation is: supported .in a variety of sections: as rioted below
as it relates to the fire'resistivity of the proposed element. The structural efficacy
of the colunv3 is established separately as part of the now approved structural
design:
• Tables. 503 and 601 clearly establish the code equivalency between our
;proposed Heavy Tinibet' usage. at the coiunins 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 inexcess of those allovied' in the type 5A building. across all
occupancy group types. This interpretation is supported. in the excerpted
section from the. IBC commentary Vol 1 on the 2003 IBC.. ..'section 602.4
States,iii the commentary
o "The interior elements are permitted.to.be unprotected because.of
the .massive element sizes anal the requirements that there riobe:
any -concealed spaces, such�`�as soffits, plenums: or .suspended
ceilings
■ (Where our proposed, columns enter such space, they'are
entering: into .a. rated: assembly,. the ,penetration of which`
p
shall'be' roperlyfire-caulked, should; a suspended ceiling
be placed as part :of the tenant work,: the wood colums will
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TYPFS OF CONSTRUCTION
nal in width, set on edge close together and laid as required
bulkheads below show windows, their frames,_ aprons 1'
for floors. Other types of decking shall be permitted to be
and show cases.
used if providing equivalent,fire resistance and structural
.7. Finished flooring applied directly to the floor slab orto
properties.
wood sleepers that are firest6pped in accordance with
602.4.6 Partitions. Partitions. shall be of solid wood can-
Section .717.2.7.
struction formed by not less than two layers .of 1 -inch (25
8. Partitions dividing portions of stores, offices or similar
mm) matched boards or laminated construction 4 inches (102.
places occupied :by one tenant only and which do not
min) thick, or of 1 -hour fire=resistance-rated construction.
establish a corridor serving an occupant load of 30 or
602.4.7 Exterior structural members, Where a horizontal
more shall be permitted to be constructed of
separation of 20 feet (6096 mm) or more is provided, wood
Elite -retardant -treated wood, 1 -hour fire -resistance -
rated construction or of wood panels or similar light
columns and arches conforming to heavy timber sizes shall
construction up to 6 feet (1829 mm) in height.
be permitted to be used externally.
602.5 Type V. Type V construction is that type,ofconstruction
9. Platforms. as permitted in Section 410.
4■
it which the structural elements, exterior walls and interior
10. Combustible exterior wall coverings, balconies, bay
walls are of any materials permitted,by this code,
or oriel windows, or similar appendages in accor-'
dance with Chapter. 14.
11. ,Blocking such as forhandrails, millwork, cabinets, and
-
window and door frames.
e
Light -transmitting plastics aspermittedby Chapter26,
arches,12..
13. Mastics and caulking materials applied to provide flexi-
ters 5 and 10..
ble seals between components of exterior wall construe-
onstructtion.
tion.
14. Exterior plastic . vencer installed in , accordance with
SECTION 603
Section 2605.2.
COMBUSTIBLE MATERIAL IN TYPE I
15. Nailing or furring strips as permittedby Section 803.4.
AND II CONSTRUCTION
16. Heavy timber as permitted by Note c, Item 2, to Table
601 and Sections 602.4.7 and 1406.3.
603.1 Allowable materials. Combustible materials shall be
17, Aggregates, component materials and admixtures as
permitted in buildings of Type I or II construction in the follow-.
permriitted by Section 703.2:2:
ing„ applications and in accordance with Sections' 603.1.1 .
18. Sprayed cementitious and mineral fiber fire -resistance -
through 603,1.3:
rated materials installed to comply with Section 1704.11.
1. Fire -retardant -treated wood shall be permitted. in:
19. Materials used to protect penetrations in fire -resistance- ,
1.1. Nonbearing partitions where the required fire -re-
rated assemblies in accordance with Section 712.
sistauce rating is 2 hours or less.
20. MateiYals used to protect joints in fire -resistance -rated
1.2, Nonbearing exterior walls where_ no fixe rating is
assemblies in accordance with Section 713.
required.
21.Materials allowed in the concealed spaces' of buildings
13. Roof .construction as permitted in Table 601,
of Type,i.and H.construction in accordance with Sec -
Note c, Item 3.
tion 717.5.
2. Thermal and acoustical insulation, other than foam plas-
22. Materials exposed within plenums complying with
tics, having a flame spread index of not more than 25.
Section 602 of the International Mechanical Code.
Exceptions:
23. StairW4yswithitiindividualdwelbngunitsand.atai�ays
1. Insulation placed between two layers of
noncombustible materials without an inter-
treated wand nrheavy'Umber cwnstructi0p in otber than
vening airspace shall be allowed to have a
'
- flame spread index of not more than 100.
a requixo means of moss,
2. Insulation installed between a finished floor
603.1.1 Ducts. The use of nonmetallic ducts shall be permit-.
and solid decking without intervening air-
ted when installed in accordance with the limitations of the
space shall be allowed to have a flame spread
Internationcil Mechanical Code.
index of not more than.200.
603.1.2 Piping. The use of combustible piping materials
3.' Foam plastics in accordance with Chapter 26.
shall be. permitted when installed in accordance with the
4. Roof coverings that have an A, B or C classification.
limitations :of the International Mechanical Code and the
5. Interior floor finish and interior finish, trim and mill-
hdCl7tatiMa Uni orae Plumbing Code.
work such as doors, door frames, window sashes and
603.1.3 Electrical. The use of electrical wiring methods
frames.
with combustible insulation, tubing; raceways and related
6. Where not. installed over 15 feet (4572 mm) above
components shall be permitted when installed in accordance
grade, show windows, nailing or furring strips, wooden
with the limitations of the IGG Seattle Electrical Code.
' 104
2003 SEATTLE BUILDING CODE
GENERAL BUILDING HEIGHTS AND AREAS
TABLE 503
ALLOWABLE HEIGHT AND BUILDING AREAS
Height limitations shbwn as stories and feet above grade plane:
,..l -A L... 4k- AMI..liinn of "A e.. hoeflAnn"nPr ft. -'
r ~� For Sl: I foot = 304.8 mm, I square foot = 0.0929 1112,
UL = Urslimited, NP m Not permitted.,
a: As applicable in Section 101.2.
b. For -open parking structtuas, see Section 406.3.
C. For private garages, see Section 406.1. `
2003 SEATTLE BUILDING CODE, .
87
TYPE OF CONSMUCTI6N
TYpE i
TYPE II -
TYPE III TYPE IV
'f E V -
-
A
1.
B
A
S
A
8 HT
A B"
M.
` GROUP
NSt(5)
UL _
- 'ISO
65
55
65 .
55 � � '65 -
50 40
A-1
S
A '
UL
UL
5
UL
3
15,500
2
8,506 1
3
14,000
2. 3
8,500 15,000
2 1
11,500 5,500
71
A2
S
A
UL'
UL
11 _
UL
3
15,500
2
9;500
3
14,000
2 3
9,500 15,000
2 1
11 ,500 fi,000
A-3
S
A
UL
UL
1[
UL
3
15,500
2.
9,500
3
14400
2 3
9,500 15,00¢
2 1
11,500 6,000
A 4 ..
S'
A
UL
UL
11 .
- LTL
3
15,500
2
9,500
3
I4,000
2 3
9,500 15,000
2 1
11,500 " 6,000
S :
UL
UL i
I
LII.
Ul
UL ' LJi
UL [1L .
A-5
A
UL
UL
U1,
_
UL
UL
UL UL
UL UL
B
S
A
UL
UL.
11
UL
5
37,500
4-
23,000
5
28,500
4 5
19,000 36,000 f
3 2
.18,000 9,000 "
S
S
A -
UL.
LlL
5
UL
3..
26,500
2
14,500 ,
3
23;500
2 3
14,500F255W
1 1
18,506 9,500
F1
S
A
UL
UL '
11 _
UL
4
25,006
2
15,500
3
19,00
2
12,000
2 .l
14,006 8,500 ,
P2
S
A
UL
UL
11
UL
5
37,500
3
2.3,000
4.
28,500•
3
18,000
3 2
21,000- 13.000
S
1
1
1
1
1
]NP
1
A
21,000
16,500
11,000
7,000'
9,500
7,000
7,500 NP
H2
SUL
A
21,000 -'
3
.16,500.
2
11,000
1
7,000
2
9,500 -
1 2
7,000 10,500
1 1
7,500 3,000'
H3
S
A
UL.
UL
6
60,000
4
26,500
2
14,000
4
17,500
2 4
13,000 25,500
2 1
10,000 5,000
S
�
7
S
3
5
3 5
3 2
H4
A
UL
UL
37,500
17,500
28,500
17,500 36,000
18,000 6,500
S
3
3
3
3 '.
3
3 3
3 2
H-5.
A
UL ..
TJL
37,500
23,000
28,500
19,000 36,000
18,000 91000
UL
9
4
3.
4
3- 4-
3' 2
IS
A
UL
'55,000
19,000
10,000
10,500
16,500
10,000 18,000
4,500
S
UL:
4
2
I
1
NP 1
1
A
U1,.
UL
15,000
11,000
12,000
NP 12,000
N
9,500 NPP
13
S
A
UL
.U1.
4
UL
2
15,000
1
10,000
2
10,500
1 2,
' 7,500 12,000
2, I
7,500 5,000
14
S
A
UL
UL
5.-'
60,500.
.3.
26,500
2
13,000.
3
23,500
2 3
13,000 25,500.
1 1.
18,500 9,000
S
A
UL
UL
11
UL
4
21,500
4
12,500
.4
18,500
4 4
12,500 20,500
3 1
14,000 9,000
S
UL
11
4
4
4
4 4
34
2
H-1
A
UL.
UL
24,000
16,000
241000
16,000 20,500
12,000
7,000
5
UL
11.
4
4
4
4 4
34
2
A
UL
UL
24,006
16,000
24,000
16,060 20,500
12,000
7.000
S
UL
11
4
4
4
4
4
34
3 -
Et -3°
A
UL
UL,
UL
UL
UL.
UL
UL
UL
UL
R-4
S
A
LII,
UL .
11
Ut.
4
24,000
4
16,000
4
24,0W
4
16,000
4
20,500
3
1 12,000
2
7,000
S-1
S
A
UL
UL
11
40,000
4
26,00D
3
17,500
3
26,000
3
17,500
4_
25,500
3
14,000
1
9,000
S fib,
S
A
UL
UL
11
79,000
5
1 39,000
4
26,000
4
39,000
4
26,000
5.
38,590
4
21,000
2
13,500
Ue
S
A
UL
S
35,500
q
19,000.
2
8,500
3
14,006
2
8,500
4
18,OOD
2
9,000
1
5,500
r ~� For Sl: I foot = 304.8 mm, I square foot = 0.0929 1112,
UL = Urslimited, NP m Not permitted.,
a: As applicable in Section 101.2.
b. For -open parking structtuas, see Section 406.3.
C. For private garages, see Section 406.1. `
2003 SEATTLE BUILDING CODE, .
87
For 5I; 1 foot = 304.8 trim.
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 which have no connection to the columns shall be considered secondary members
and not a part of the structural frame.
b.- Roof supports: Fire -resistance ratings of structural frame and bearing walls.are permitted to,be.reduced by 1 hour where supporting a roof only.
c. 1. •Except in Factory -Industrial (11-1), Hazardous (Id), Mercantile (M) and Moderate -Hazard Storage (S-1) occupancies,' fire protection of structural members
shall notberequired, including protection o€roof framing anddecking'where everypart of the roofconstrirction is 20fector more ab6ve any floor immediately
below. Fire -retardant -treated wood members shall be allowed to be•used for such unprotected members.
'2. In all occupancies, heavy timber. shall be altowed.where a 1 -hour oz less fire -resistance rating is required.
3; In Type I and 11 constmctiori, fire -retardant -treated wood shall be allowed in buildings including girders and trusses as part of the roof construction when the
building is:
I. Two stories or less in. height;
ii. Type H construction over two stories; or
iii. Type I construction over two. stories and the vertical distance from the upper floor to the roof is 20 feet or more.
d. An approved automaticsp'rinklersysteminaccordance.withSection903:3.1.1shallbeallowedtobesubstitutedforl-hourfire-resistance-ratedconstii+ctian, b
vided such systemis not otherwiserequired by otherprovisions of the code or used for an allowable area increase in accordance with Section 506.3 or anallowale
height increase in accordance with Section 504.2. The 1 -hour substitution for the f re resistance of exterior walls shall not be permitted. This substitution shall not
be permitted irl bulldings 6onstruGtd according to Serflon 1018.2 ex= on 4.
c• 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). ,.
2003 SEATTLE BUILDING CODE
105
TYPE I
TYPE 11
TYPE III
TYPE IV TYPE V
A
t3
0
B
Ad -
B
T d B
BUILDING ELEMENT
Structural frame'
.
Ineludirig columns, ' ders, trusses
3b
2"
1
0
1 ''
0
! HT • 1 0
Bearing walls
Exterior,
Interior
3
3b
2
2b
I
1
0
0
2
1
2
0
2 1 0
1/HT 1 0
Nonbcaring walls and partitiobs .
Exterior
See Table 602
Nonbearing walls and partitions
Interior`
0
0
0
0
00
See Section 602.4.6
0
0
Floor construction
Including suppbrdng beatns and'oists
2
2
Q
1
0
HT
1
0
Roof construction
Including su orting beams and joists
11/2u
1°
le
0`
1°
0
HT
1`.,
0
For 5I; 1 foot = 304.8 trim.
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 which have no connection to the columns shall be considered secondary members
and not a part of the structural frame.
b.- Roof supports: Fire -resistance ratings of structural frame and bearing walls.are permitted to,be.reduced by 1 hour where supporting a roof only.
c. 1. •Except in Factory -Industrial (11-1), Hazardous (Id), Mercantile (M) and Moderate -Hazard Storage (S-1) occupancies,' fire protection of structural members
shall notberequired, including protection o€roof framing anddecking'where everypart of the roofconstrirction is 20fector more ab6ve any floor immediately
below. Fire -retardant -treated wood members shall be allowed to be•used for such unprotected members.
'2. In all occupancies, heavy timber. shall be altowed.where a 1 -hour oz less fire -resistance rating is required.
3; In Type I and 11 constmctiori, fire -retardant -treated wood shall be allowed in buildings including girders and trusses as part of the roof construction when the
building is:
I. Two stories or less in. height;
ii. Type H construction over two stories; or
iii. Type I construction over two. stories and the vertical distance from the upper floor to the roof is 20 feet or more.
d. An approved automaticsp'rinklersysteminaccordance.withSection903:3.1.1shallbeallowedtobesubstitutedforl-hourfire-resistance-ratedconstii+ctian, b
vided such systemis not otherwiserequired by otherprovisions of the code or used for an allowable area increase in accordance with Section 506.3 or anallowale
height increase in accordance with Section 504.2. The 1 -hour substitution for the f re resistance of exterior walls shall not be permitted. This substitution shall not
be permitted irl bulldings 6onstruGtd according to Serflon 1018.2 ex= on 4.
c• 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). ,.
2003 SEATTLE BUILDING CODE
105
CHAPTER 6..
103 1i
TYPES OF CONSTRUCTION
SECTION 601
602.4.2 Floor framing. Wood beams and girders shall be of
GENERAL
ssawn,or glued -laminated timber and shall be not less than 6
601.1 Scope. The provisions of this 'chapter shall control the
inches (152 mm) nominal in width and not less. than 10.
inches (254 .mm) nominal, in -depth. Framed sawn or
classification of buildings as to type of construction.
glued -laminated timber arches, which spring from the floor
line and support floor loads, shall be not less than 8 inches
SECTION 602
(203 mm) nominal in any dimension. Framed timber trusses
CONSTRUCTION CLASSIFICATION
supporting floor loads shall have members of not less 4hau8
inches (203 mm) nominal in any dimension.
602.1 General. Buildings and structures erected .or to be
erected, altered or extended irr Height or area shall be classified
602.4.3 Roof framing. Wood -frame or glued -laminated
in one of the five construction types defined in Sections 602.2
arches for roof construction, which spring from the floor
line or from grade and do not support floor loads, shall have
through 602.5.. The building elements shall have a
members not less Than 6 inches (1,52 mm) nominal in width,
fir resistance rating not less than that specified in Table 601
and have less Than 8 inches mm) nominal in depth for
and exterior walls shall. have a fire-iesistahce ratirig not less
,(203
the lower half of the height and not less than 6 inches (152
than that specified in Table 602..
mm) nominal in depth for the upper half, Framed or glued -
602.1.1 Minimum regirirernerits. A building or portion
laminated arches for roof construction that.spring from the
thereof shall not be required to conform to the details of a
top of walls or wall abutments, framed timber trusses and
type of construction higher than that type, which meets the
other roof framing, which do not support floor loads,, shall
minimum requirements based on occupancy even though
have members not.less than 4 inches (102 mm) nominal in
certain features of such a building actually 'conform to a
width andnot less than 6 inches (152 mm) nominal in depth. .
highertype of construction.:
Spaced members shall be permitted to be composed of two
602.2 Types I anti H. Type I azid 11 construction are those types
or more pieces not less than 3 inches (76 mm) nominal in
of construction in which the building elements listed in Table
-thickness where blocked solidly throughout their interven-
601 are of noncombustible materials.
ing spaces or where spaces are tightly closed by a continu-
Type M. Type Mconstruction is that type of construe-
wood cover plate of not less than} 2 inches (51 mm)
ous602.3 in thickness secured to the underside of the mem-
tion in which the exterior walls are of noncombustible znateri-
nominal
1�ers. Splice plates shall be not less than 3 inches, (76 min).
als and. the interior building elements are of any material
nominal in thickness. Where protected. by approved auto -
by this code. Fire -retardant -treated wood framing
permitteduratic
sprinklers under the roof deck, framing members
.complying with Section 2303.2 shall be permitted within. exte-
shall be not less than 3 inches (76 mm) nominal in width.
rior wall assemblies'of a 2 -hour rating or less,
602.4.4 Floors. Floors shall be without concealed spaces.
2.3* Z= JIJA buildings may includ
Wood floors shall be of sawn or glued-larhinatcd planks,
posed heayy-fimber ' -
splined or. tongue and -groove, of not less than 3 inches (76
'exceptmm)
nominal in thickness covered with 1 -inch (25 mm)
fim-resistivo constraWon required by Section 707 and.
nominal dimension tongue -and -groove flooring, laid cross -
Chanters and.l
wise or diagonally, or 0.5-in6h (12.7 mm) particleboard or
planks notless than 4 inches (102 mm) nominal in width set
602.4 Type I.V. Type'IV construction (Heavy Timber, HT) is
on edge close together. and well spiked and covered with '
flooring 15/32:inch J
that type of construction in which the exterior walls are of
Much .(25 mm) nominal dimension or
'or.
noncombustible materials and the interior building elements
(12 mm) wood structural panel 0.5 -inch (12.7. MM)
are of solid or laminated wood without concealed spaces. The
particleboard. The lumber shall be laid so that no continu-
details of Type IV construction shall comply with the provi-
ous line of joints will occur except at points of support..
sions of this section. Fire -retardant -treated wood framing com-
Floors shall. not extend closer than .0.5 inch (12,7 mm) to
plying with Section 2303.2 shall be permitted within exterior
walls: Such 0.5-in6h (12.7 mm) space shall be covered by a
wall assemblies with a 2 -hour rating or less:.
molding fastened to the wall and so arranged that it will not
602.4.1 Columns. Wood columns shall be sawn or glued
obstruct the swelling or shrinkage movements of the floor. ,
Corbeling of masonry walls under the floor shall bepermit-
laminated and shall not be less than 8 inches (203 nim),
ted to;be used in place of molding.
nominal; in any dimension where supporting floor loads and
not less than 6 inches (152 mem) nominal in width and not
642.4.5 Roofs. Roofs shall be without concealed spaces and
'less than 8 inches'(203 mm) nominal in depth where sup- .
wood roof decks shall be sawn or glued laminated, splined
porting roof and ceiling load's only. Columns shall -be con-
or tongue -and -groove plank, not less than 2 inches (51 mm)
tinuous or superimposed and connected in an approved
thick, 1118 -inch -thick (32 mm) wood Structural panel (exte-
manner,
rior glue), or of planks not less than 3 inches (76 mm) nomi -
2003 SEATTLE BUILDING CORE
*"PES OF CONSTRUCTION
I
assemblies. For example, the required rating for strut-
itural frame members in Type IA construction is 3 hours,
<'for Type IB is 2 hours, for Type IIA is 1 hour and for Type .
kio 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 lA
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
rnember 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.
Section 603.1, Item 18 and in Section 703.2.2.
;Fire -retardant -treated wood (FRTW), although combus-
4!ble, is permitted in limited uses in buildings of Type I
'end 11 construction (see Section 603 and Table 601,
%Note C). While FRTW is permitted in certain applica-
tians in buildings of Type I and 11 construction, it is not
'assumed to be fire -resistance rated, and generally does
snot afford any higher fire -resistance rating than un-
ireated wood material.
642.3 Type III. Type III construction is that type of construction
i6,which the exterior walls are of noncombustible materials and.
the -interior building elements are of any material permitted by.
thiftode. Fire -retardant -treated wood framing complying with
Section 2303.2 shall be permitted .within exterior wall assem-
Wl s of a 2 -hour rating or less.
+,+t'buildings of Type ill construction are made with both com
66stible and noncombustible materials. The exterior walls
are required to be noncombustible with load-bearing exte-
4ibr walls required to have,a minimum 2 -hour fire-resis=
46hce rating. Exterior. nonload-bearing walls are not -
I required by Table 601 to have a fire -resistance rating, but
1;ust comply with the provisions of Table 602. The interior
dements (i.e., floors, roofs and walls) are permitted to be
of combustible materials. An example of a typical building
erfType III construction is a structure having its exterior
I&Als constructed of concrete, masonry or other approved
a 0}
6ricombustible materials, .but with a wood -frame floor
...{j l and roof construction (see Figure 602.3 for an example of
Type III construction).'Type III construction is further di.
oylded into two subclassifications: Types IIIA and 11113: An
&le of a building of Type IIIA construction is one in
M,hich the interior load-bearing walls, floors, roofs [those
embers that are less than 20 feet (6096 mm) to the low -
pmember] and all structural members are protected to
=rovide a minimum 1 -hour fire -resistance rating. The
structural members of a building of Type IIIB construction
9ceptp not required to have a fire -resistance rating with the
ion
of the exterior load-bearing walls.
Although FRTW does not meet the specifications of
code as,a noncombustible material, it is permitted
as a substitute for noncombustible materials in exterior
fall assemblies of Type ill construction. While the exte-
p .....,.kior walls are permitted to be either nonload bearing or
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.
gGYPSV
WALLBOARD
WOOD RAFTERS•'}t]I[.
ANOTRIM �} FURRED PANELING
;•i _. - i' CONCRETE OLOOK
GYPSUM WALLBOARD
BRICK'' Q��r� -
s Yj . WOODJOIST AND FLOOR
Figure 602.3
EXAMPLE OF TYPE 111 CONSTRUCTION
642.4 Type IV Type TV construction (Heavy Timber, HT) is that
type of bonstruction in which the exterior walls ale of
noncombustible materials and the interior building 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 complying
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
IVHT construction. HT construction requires the exte
rlor walls to be constructed of noncombustible materi-
als. The interior elements are required to be constructed
of solid or laminated wood without any concealed
spaces. ATI- of'the. combustible structural elements are
permitted to be unprotected because of the massive el-
ernent sizes and the requirement that there not be any
concealed spaces, such as soffits, 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 Ty pe.IV 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
underfire 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
wails are permitted to be either nonload bearing or load
bearing, they must have a fire -resistance rating of no.
greater than 2 Fours where FRTW is used in the exterior
wall. FRTW is required to comply with the provisions of
TIONAL BUILDING CODE" COMMENTARY 6-3
602.4.1 -- 602.4.3 TYPES OFCON
Section 2303.2.
It should be noted that the sizes of specified timber
members are'nominal. Actual sizes for sawn timbers will
generally be 112 inch (12.7 mm) to 3/4.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.
Nominal
.3
4
6
8
10
12
14
16
(inches)
10 -inches (254 mm) deep. Both framed timber truss"
supporting floor loads and framed sawn or.glued larp'
nated tlmber arches that spring from the floor line ora
support floor loads are required to be at least 8 mcli
f
Actual
21/4
31/5
51/3
631,
83/4
10%
121/4
141/4
(inches)
For Sl: 1 inch = 25.4 mm.
Figure 602.4
NOMINAL VERSUS ACTUAL DIMENSIONS FOR
GLUED -LAMINATED MEMBERS
602.4.1 Columns. Wood columns shall be sawn or glued lami-
nated and shall not be less than 8 inches (203 mri1), nominal, in
any dimension where supporting floor loads and not less than 6
inches (152 mm) nominal in widthand not less than 8 in,
(203 mm) nominal in depth where supporting roof and ceiling
loads only; Columns shall be continuous -or superimposed and
connected in an approved manner.
4, Minimum construction requirements and dimensions for
timber columns are. provided in this section: Columns
are required to be a minimum of S 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 byilding. The design engineer or architect must pro-
vide details of all column connections; As with ail 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 less than 6
inches (152 mm) nominal in width and not less than 10 inches
(254 mm) nominal in depth. Framed sawn or glued -laminated
timber arches, which spring from the floor line and support floor
loads, shall be not less than 8 inches .(203 min) nominal in any
dimension. Franied timber, trusses supporting floor loads shall
have members. of not less than 8 inches (203 mm) nominal in
any dimension.
❖ Minimum construction requirements and dimensions for
floor framing are provided in this section. Girders are
602.4.3 Roof framing. Wood -frame or glued -laminated arcl
for roof construction, which.spring from the floor line or fr
grade and do not support floor loads, shall have, members
less than 6 inches (152 mm) nominal in width, and have less ti
8 inches (203 mm) nominal in depth for the lower half of
height and not less than 6 inches (152 mm) nominal in depth
the upper half. Framed or ghied-laminated arches.for roof c.
struction that spring from the top of walls or wall abutniei
framed timber trusses and other roof framing, which do not s
port floor loads, shall have members not less than 4 inches (:
mm) nominal in width and not lesvthan 6 inches (152 mm) nc
inal in depth. Spaced members shall be permitted, to be cc
posed of two or more pieces not less than 3 inches (76 rr
nominal in thickness where blocked solidly throughout their
tervening spaces or where spaces are tightly closed by a con ti
ous wood cover plate of not less than -2 inches (51 mm.) nomi
in thickness secured to the -underside of the members. Sp:
plates shall be not less than Tinches (76 mm) nominal in th€
ness. Where protected by approved automatic sprinklers un
the roof deck, framing members shall be not less than 3 inc
(76 mm) nominal in width.
tr
•A Minimum construction requirements and dimensions 1
arches and other types of roof framing are provided
this section_ Other types of roof framing included in tl
section. -are heavy timber trusses with spaced membe
When the members of a heavy timber truss are split a
placed on either side of a main member, such as a w
connecting a chord, each component of the web mt
be 3 inches (76 mm) or more in nominal thickness: T
space between the two web members must be pi
tected with a 2 -Inch -thick (51 mm) cover plate [see F
ure 602.4:3(1)], or solidly filled with blocking [see Figs
602.4.3(2)]. The size of the roof framing members is c
pendent on the. configuration used and is regulated
this section.
If a building Of Type iV construction is equipped w
approved automatic sprinklers under the roof deck, t
minimum size of the roof framing members its reduc
to 3 inches (76 mm). Roof framing members of a smal
size will have a lower resistance to fire than the 6 -in
by 8-inch(152 mm by,203 mm) or 4 -inch by 6 -inch (1
mm by 152 mm) members required by this section. T
tradeoff allowing smaller roof framing members wh
the building is equipped with an automatic sprinklers,
tem is consistent with the concept of maintaining "equ
alent risk" for the building.
the principal horizontal structural members that suppo .
columns or beams. Beams are the structural melnb6fi
'
that support a floor or roof. Both girders and.beams av'
be inches mm)
'<
required to a minimum 6 (152 wide a
10 -inches (254 mm) deep. Both framed timber truss"
supporting floor loads and framed sawn or.glued larp'
nated tlmber arches that spring from the floor line ora
support floor loads are required to be at least 8 mcli
f
(203 mm) in any dimension.
602.4.3 Roof framing. Wood -frame or glued -laminated arcl
for roof construction, which.spring from the floor line or fr
grade and do not support floor loads, shall have, members
less than 6 inches (152 mm) nominal in width, and have less ti
8 inches (203 mm) nominal in depth for the lower half of
height and not less than 6 inches (152 mm) nominal in depth
the upper half. Framed or ghied-laminated arches.for roof c.
struction that spring from the top of walls or wall abutniei
framed timber trusses and other roof framing, which do not s
port floor loads, shall have members not less than 4 inches (:
mm) nominal in width and not lesvthan 6 inches (152 mm) nc
inal in depth. Spaced members shall be permitted, to be cc
posed of two or more pieces not less than 3 inches (76 rr
nominal in thickness where blocked solidly throughout their
tervening spaces or where spaces are tightly closed by a con ti
ous wood cover plate of not less than -2 inches (51 mm.) nomi
in thickness secured to the -underside of the members. Sp:
plates shall be not less than Tinches (76 mm) nominal in th€
ness. Where protected by approved automatic sprinklers un
the roof deck, framing members shall be not less than 3 inc
(76 mm) nominal in width.
tr
•A Minimum construction requirements and dimensions 1
arches and other types of roof framing are provided
this section_ Other types of roof framing included in tl
section. -are heavy timber trusses with spaced membe
When the members of a heavy timber truss are split a
placed on either side of a main member, such as a w
connecting a chord, each component of the web mt
be 3 inches (76 mm) or more in nominal thickness: T
space between the two web members must be pi
tected with a 2 -Inch -thick (51 mm) cover plate [see F
ure 602.4:3(1)], or solidly filled with blocking [see Figs
602.4.3(2)]. The size of the roof framing members is c
pendent on the. configuration used and is regulated
this section.
If a building Of Type iV construction is equipped w
approved automatic sprinklers under the roof deck, t
minimum size of the roof framing members its reduc
to 3 inches (76 mm). Roof framing members of a smal
size will have a lower resistance to fire than the 6 -in
by 8-inch(152 mm by,203 mm) or 4 -inch by 6 -inch (1
mm by 152 mm) members required by this section. T
tradeoff allowing smaller roof framing members wh
the building is equipped with an automatic sprinklers,
tem is consistent with the concept of maintaining "equ
alent risk" for the building.