Ethan Martin, PE WoodWorks – The Wood Products Council
“The Wood Products Council” is a Registered Provider with The American Institute of Architects Continuing Education Systems (AIA/CES). Credit(s) earned on completion of this program will be reported to AIA/CES for AIA members. Certificates of Completion for both AIA members and non-AIA members are available upon request. This program is registered with AIA/CES for continuing professional education. As such, it does not include content that may be deemed or construed to be an approval or endorsement by the AIA of any material of construction or any method or manner of handling, using, distributing, or dealing in any material or product.
Questions related to specific materials, methods, and services will be addressed at the conclusion of this presentation.
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At the end of this program, participants will be able to:
1. The participants will understand the Building Code requirements for
designing a 5-story wood-frame multi-family project.
2. The participants will understand the Building Code requirements for
designing a 6-story mixed-use project with the top 5 floors wood framing.
3. The participants will understand height and area limitations of designing 5-
story wood- framed multi-family buildings.
4. The participants will understand the construction challenges of building 5-
stories of wood framing, including shrinkage, fire protection, and sound
transmission.
What is Mid-rise?
626 Dekalb Avenue, Atlanta, GA Matt Church - Davis Church Structural Engineers
(2009 IBC)
What is Mid-rise?
626 Dekalb Avenue, Atlanta, GA Matt Church - Davis Church Structural Engineers
GRADE PLANE. A reference plane representing the average of finished ground level adjoining the building at exterior walls. Where the finished ground level slopes away from the exterior walls, the reference plane shall be established by the lowest points within the area between the building and the lot line or, where the lot line is more than 6 feet (1829 mm) from the building, between the building and a point 6 feet (1829 mm) from the building.
HEIGHT, BUILDING. The vertical distance from grade plane to the average height of the highest roof surface.
(2009 IBC)
What is Mid-rise?
IBC 2006 SECTION 403 HIGH-RISE BUILDINGS 403.1 Applicability. The provisions of this section shall apply
to buildings with an occupied floor located more than 75 feet (22 860 mm) above the lowest level of fire department vehicle access.
IBC 2009 SECTION 202 DEFINITIONS HIGH-RISE BUILDING. A building with an
occupied floor located more than 75 feet (22 860 mm) above the lowest level of fire department vehicle access.
880 Glenwood Avenue, Atlanta, GA Matt Church - Davis Church Structural Engineers
(2006 & 2009 IBC)
What is Mid-rise?
ASCE 7-05 Structure- Footnote c: Heights are measured from the base of the structure as defined in Section 11.2 BASE: The level at which the horizontal seismic ground motions are considered to be imparted to the structure.
(2006 & 2009 IBC)
What is Mid-rise? OCCUPANCY-
R-1 Hotels R-2 Dormitory R-2 Multi-family
Apts., condos, affordable housing??
R-2 Assisted Living Nursing Homes R-4 Assisted Living (Except Alzheimer patients) R-2 , B, & M Mixed-use ALL???? – multi-story
626 Dekalb Avenue, Atlanta, GA Matt Church - Davis Church Structural Engineers
Building Valuation Data
Avalon Anaheim Stadium Luxury apartments (CA) Five stories of wood-frame Concrete “podium” deck. AvalonBay Communities 251 apartment units, 13,000 sf of
retail and restaurant space, and two levels of subterranean parking.
Photo by Michael Arden
Code Basics 2010 Check local jurisdictions
Fire Protection Basics Where Does the Code Allow Wood? Typical Rated Assemblies
Resources Heights and Areas
Open Frontage Sprinklers
Fire Walls Building Examples
Presentation Overview
Governing Codes for Wood Design
2006 IBC (International Building Code)
2009 IBC (International Building Code)
Code Basics
(2006 IBC)
2009 IBC Heights and Areas
(2009 IBC) (2009 IBC)
Exceptions to the Tabular Areas
Unlimited area buildings Mezzanines Pedestal buildings Special provisions
Unlimited Area Buildings
Section 507 For all types of construction:
Unsprinklered buildings: Limited to one story F-2 & S-2 with frontage at least 60’ in width
Sprinklered, 1 story: B, F, M & S with yards at least 60’
Exceptions for some uses
Sprinklered, 2 story: -- B, F, M, & S
Check section for more details
Fire Protection Basics
Protected or Unprotected Structural Members
Are structural members potentially exposed to flames.
Construction Type I-V Are the structural members considered Non-Combustible or Combustible
Amount of Protection Provided Unrated gypsum walls and floors One hour wall and floor assemblies Two hour rated assemblies
Key Considerations
Basic assumption is that fires begin at the interior and rated wall assemblies are not required for the exterior (non-bearing)
Basic Principles Exterior Rated Walls
Interior
Exterior
Fire Protection on Inside of Building
When proximity to other buildings decreases fire protection is needed on the building exterior walls
Basic Principles Exterior Rated Walls
Interior
Exterior
Fire Protection on Exterior Walls When < 30’
X < 30’
Lot Line
Table 601 & 602
IBC 2009 Table 601
Table 601 Table 602 establishes requirements For structures separated by 10’-30’ they are typically 0 or 1 hour rated
Exterior Rated Assemblies
(2009 IBC)
The 2006 IBC (as does the 2009 IBC) has category A and B or Protected (rated) and Unprotected (non-rated), respectively. What makes wood protected or Type A? Fire rated gypsum sheathing on walls and floor/ceilings
Unprotected buildings, type B, would be exposed members that do not fall under Type IV Heavy Timber Construction.
Protected vs. Unprotected
(2006 & 2009 IBC)
Protected vs. Unprotected
Unprotected
WSP WSP
Unprotected
½” Gyp.
Protected
½” Gyp.
5/8” Type X
Gyp.
5/8” Type X
Gyp.
Where does the building code allow specification of wood framing for mid-rise?
CONSTRUCTION TYPES
• The 2006 & 2009 IBC allows for five types of construction.
• A given use and occupancy can be built using any type of construction.
• Types I and II are generally noncombustible inside and out - materials such as concrete.
• Types III have noncombustible exteriors with interiors of any material.
• Type IV &V are generally combustible such as wood although V permits any material permitted.
Generally the less combustible the larger square footage and number of stories allowed.
Construction Types
Types of Construction in the IBC Given a building type we can determine the level of
protection needed. (IBC Section 601)
Construction Types
(2009 IBC)
IBC 602.3 TYPE III Noncombustible (Ext.) &
Combustible (Int.)
• So where can wood go? Almost anywhere!.
• Exterior Walls need to be non-combustible or FRT Wood (2 hour or less)
• Interior any material permitted by code.
• Heavy Timber Roof • Be careful with wall/
floor interface
Type III Construction
(2006 & 2009 IBC)
• All structural elements can be combustible construction.
• (FRTW ext. walls)
Type IV
(2006 & 2009 IBC)
In a variety of ways the building code does recognize the ability for Heavy Timber to resist fires through charring.
Type IV – Heavy Timber
Performance of Wood vs. Steel
Walls are to be non-combustible. (FRT ext. walls < 2hr.) The IBC has published minimum sizes for a structure to be Heavy Timber. Detailed provisions available from AWC and APA.
Type IV – Heavy Timber
8x in any dimension
(2006 & 2009 IBC)
• All structural elements can be combustible construction.
Type V
(2006 & 2009 IBC)
Type V is primarily wood construction. Examples where wood may be utilized include:
Rated wall and floor framing and sheathing in protected construction. Unrated walls and floors with or without sprinklers*
• For a 5 story sprinklered building; Using type IIIA; B, F-2, H-3, I-1, M, R, S-2. Offices, Assisted Living, Mercantile, and Residential
Common Examples Building Height
• For a 4 story sprinklered building; Using type IIIA; A, E, F-1, H-5, I-4. Examples include assembly areas, and schools.
Common Examples Building Height
Mezzanine An intermediate level or levels between the floor and ceiling of any story and in accordance with IBC Section 505.
Mezzanines
Not counted toward building area or height Does count toward fire area (Related to fire protection – Ch. 9)
Maximum 1/3 floor area of room or space where located Special egress provisions apply Must be open and unobstructed to room in which it’s located (walls ≤ 42” allowed) Several exceptions
Slightly different for equipment platforms
Section 505
• A basement and/or the first story above
• grade plane of a building shall be considered as a separate and distinct building
• Additional Concrete Story Allowed
• Overall height requirements must be maintained
• 60’ + 20’ = 80’
Podium Structures – IBC Section 509
10’
10’
10’ 10’
10’
10’
Podium Structures Sections 509.4 & 509.5 Group R Occupancy above parking garage Parking garage: Type I Height of R measured from floor above garage Fire-resistance rating between occupancies Type IIIA const & R-1 or R-2 Height increase to 6 stories (75 ft)
3 hr fire rating between garage & floors above Floor area of building above subdivided
For other occupancies see Sec. 509
Podium Structure Pedestal Buildings
Special Provisions
“Separate” buildings (Sec. 503.1) Each portion of a building separated by one or more fire walls shall be considered a separate building.
STREET
Property Line
Bldg 1 Bldg 2 Bldg 3 Bldg 4
F-1 F-2 F-3 F-4
F = frontage
Special Provisions -- Sec. 509 Permits use of special conditions exempt from, or that modify, requirements of chapter. Horizontal building separation (Sec. 509.2)
Permits buildings to be separate buildings for area, height, and type of construction Podium/Pedestal building w/ choices of occupancies All of the conditions must be met
3-hr horizontal separation Building below separation no more than 1-story & Type IA const Openings thru separation require shaft protection Specific occupancy groups permitted below & above separation Maximum height limited
Special Provisions -- Sec. 509 (cont’d)
Other sections: Various occupancies above parking garages Sec. 509.2 permits various occupancies in lower story
Each subsection independent of each other
(2006 IBC)
Heights and Areas
• Stories • Square Footage
• Sprinklers • Open Frontage • No Firewalls
How big can a wood frame structure be?
What factors into determining allowable heights and areas Occupancy Construction Types Protected or Unprotected Open Frontage Sprinklers Fire Walls/Barriers
Wood Framing & Heights & Areas
For a given occupancy, building codes allow the size of a structure to increase based on its level of non combustibility, overall fire resistance, and fire-fighting access. Types I and II are considered non-combustible
Type I often allows for an unlimited building size Type II, III, IV and V will have varying degree of size allowed based on:
• Protected vs. Unprotected • Proximity to Other Buildings • Use of Sprinklers
Fire Provisions and Building Size
2009 IBC Heights and Areas Assume an unprotected multi-family building is desired – Group
R-2
For Type IB 11 stories/UL sf is allowed. For Type IIB 4 stories/16,000sf is allowed. For Type IIIB 4 stories/16,000sf is allowed. For Type IV 4 stories/20,500sf is allowed. For Type VB 2 stories/7,000sf is allowed.
Building Size Example I
TABLE 503
(2006 & 2009 IBC)
AREA MODIFICATIONS IBC 506 Aa = {At + [At x If] + [At x Is] } (Equation 5-1)
Aa = Allowable building area per story (sq. ft.) At = Tabular building area per story (Table 503) (sq. ft.) If = Area increase factor due to frontage (IBC 506.2) Is = Area increase factor due to sprinkler protection (IBC 506.3)
(2006 & 2009 IBC)
506.4 Area determination Two stories above grade:
Maximum Area = Aa x 2 Three stories or more above grade:
Maximum Area = Aa x 3 Story <= Aa
Exception: 1. Unlimited area bldgs. per 507 2. Bldgs. w/approved sprinklers
Maximum Area = Aa x no. stories above grade
Maximum Area
(2006 IBC)
IBC 506.2 - Allowable size of building may increase where open frontage is provided.
Frontage Increase
(2006 & 2009 IBC)
• If = [F / P – 0.25] W / 30 (Section 506.2) • F = Building perimeter that fronts on a public way or
open space having 20 feet open minimum width (feet).
• P = Perimeter of entire building (feet). • W = Width of public way or open space (feet) in
accordance with Section 506.2.1. 0
Frontage Increase
> 30’
15’
> 30’
> 25’
Frontage Increase
25’ > 30’
> 30’ > 15’
NO INCREASE
PARTIAL INCREASE 20’ TO 30’
MAX INCREASE
MAX INCREASE
100’ 60’ If = [F / P – 0.25] W / 30 For a 100’ x 60’ building
F = 60’ + 100’ + 60’ + 0 = 220’ P = 100’ + 100’ + 60’ + 60’ = 320’ W = (30’*60’+25’*100’+30’*60’) / 220’ = 27.7ft
If = [220’ / 320’ – 0.25] 27.7/ 30 = 0.40 Aa = {At + [At x If] + [At x Is] } (Equation 5-1)
Frontage Increase - Example
40’
15’
30’
25’
(< 20’ – N.G.)
(30’ max)
(2006 & 2009 IBC)
The IBC sprinklers use is not generally required based on construction type or occupancy. Sprinklers can be used to increase heights and areas as well as reduce fire rated requirements. (Section 903 does have requirements for sprinklers – some Assembly, Emergency , Institutional, Hazardous, etc.) Be aware of local and state requirements! e.g. adoption of NFPA 101.
Sprinkler Requirements Automatic Sprinkler System Increase!
IBC 504.2 Where a building is equipped throughout with an approved sprinkler system
maximum height is increased by 20 feet maximum number of stories is increased by one.
Combined with Frontage increase 506.2 Can be combine with 506.3 Sprinkler increase
Group R w/ NFPA 13R inc. 20 ft. and one story – Max. 60 feet & 4 stories
Group R w/ NFPA 13 – Max. 65 feet & 5 stories.
(2006 & 2009 IBC)
Automatic Sprinkler System Increase!
IBC 504.2 Where a building is equipped throughout with an approved sprinkler system
maximum height is increased by 20 feet maximum number of stories is increased by one.
Combined with Frontage increase 506.2 Can be combine with 506.3 Sprinkler increase Exception: 1. Group I-2 occupancy of Type IIB, III, IV or V
construction. 2. Group H-1, H-2, H-3 or H-5 occupancy. 3. Fire-resistance rating substitution in accordance
with Table 601, Note d. (2006 & 2009 IBC)
What Sprinklers Cannot Do!
A sprinkler system used to increase heights (Section 504.2) OR area increase (Section 506.3) Cannot also be used to lower fire-resistance by substitution (Table 601, Note e).
It can do either, but not both!!
Example
Assume an unprotected multi-family building is desired – Group R-2
For Type IB 11 stories/UL sf is allowed. For Type IIB 4 stories/16,000sf is allowed. For Type IIIB 4 stories/16,000sf is allowed. For Type IV 4 stories/20,500sf is allowed. For Type VB 2 stories/7000sf is allowed.
Building Size Example I
TABLE 503
Frontage Increase
25’ > 30’
> 30’ > 15’
NO INCREASE
PARTIAL INCREASE 20’ TO 30’
MAX INCREASE
MAX INCREASE
100’ 60’
For a multi-story R-2 building • For type IIIB (unprotected) construction w/sprinklers:
Tabulated area At is 16,000sf Aa = {At + [At x If] + [At x Is] } (Equation 5-1) Aa = {16,000 + [16,000 x 0.40] + [ 16,000 x 2] } Aa = 54,400sf/story Increase from 4 to 5 stores
• For type IIIA the same building would be: Aa = {24,000 + [24,000 x 0.40] + [24,000 x 2] } Aa = 81,600sf/story Increase from 4 to 5 stories
• For type IIIA the same building (75% max.)would be: • Aa = {24,000 + [24,000 x 0.75] + [24,000 x 2] } • Aa = 90,000sf/story 5 story building
Total Frontage & Sprinkler Increase
506.4 Area determination Three stories or more above grade:
Maximum Area = Aa x 3 Story <= Aa
Exception: 1. Unlimited area bldgs. per 507 2. Bldgs. w/approved sprinklers
Maximum Area = Aa x no. stories above grade
Max. area= 90,000 sq. ft. x 5 stories = 450,000 sq.ft.
Maximum Area
R-2 Maximum Area 3 stories VA Protected Tabulated area At is 12,000sf
Aa = {At + [At x If] + [At x Is] } (Equation 5-1) Aa = {12,000 + [12,000 x 0.75] + [ 12,000 x 2] } Aa = 45,000sf/story
506.4.1 Area determination. The total allowable building area is: 1. For buildings with two stories above grade plane , multiply by 2; 2. For buildings with three or more stories above grade plane , multiply by 3;
Building Size Example 2
R-2 Allowable Areas Type VA
Building Size Example 2 R-2 Allowable Areas Type IIIB Building Size Example 3
R-2 Allowable Areas Type IIIA
Building Size Example 4
• Podiums • Sprinklers • Mezzanine • For B 65 + 20 = 85 • Tabulated # stories 5 allowed • Type IIIA
How tall can we be?
10’
10’
10’
10’
10’
10’
10’
Typical Rated Assemblies
IBC 703 Where rated assemblies are required the IBC allows various methods for approval. IBC Section 703.2 Tested assemblies – tested in accordance with ASTM E119 or UL 263 IBC 703.3 Alternate Methods
IBC Section 720 Deemed to comply tables (prescriptive) IBC Section 721 Calculated Fire Resistance (references Ch. 16 ANSI/AF&PA NDS)
Typical Rated Assemblies
(2009 IBC)
Testing Agencies American Wood Council has accepted wood floor and wall assemblies in their free publication DCA3. www.awc.org
Tested Assemblies – DCA3
APA has accepted wood floor and wall assemblies in their free publication W305. www.apawood.org
Tested Assemblies – W305
Example: To achieve a one hour rating from one side DCA 3 Assembly WS6-1.5 2x6@16” o.c., R-19 Fiberglass-insulation, 5/8” Type X Gypsum Wallboard, 2-1/4” Type S screws at 12” o.c.
Example: To achieve an one hour rating from the bottom side. I-Joists at 24”o.c. Two layers 1/2” Gypsum Wallboard, 1-1/4” Type S screws at 12” o.c.
Typical Floor Assembly Attributes
For plated floor trusses Wood Truss Council has details available. www.sbcindustry.com
Typical Floor Assembly Attributes
Example: 2x6 Interior one hour wall with 5/8” Type X Gypsum.
IBC Tabulated Assemblies
l, m
Footnote m: Design stress reduced to 78% of F’c
(2006 and 2009 IBC)
IBC 721 Calculated Fire Resistance
721.6 Wood Assemblies (Component Additive Method)
721.6.3 Design of fire-resistant exposed wood members.
(2006 and 2009 IBC)
IBC 703.3 allows engineering analysis based on a comparison of building element designs having fire-resistance ratings as determined by the test procedures set forth in ASTM E 119.
Component Additive Method
(2006 & 2009 IBC)
Chapter 7 of IBC (703.3, 721.6, & Table 721.6.2(1)) Also in DCA 4 available at www.awc.org.
Example: ½” Gypsum will provide 15 minutes of resistance.
Component Additive Method
(2006 & 2009 IBC)
In addition to sheathing structural members have resistance to fire. IBC Table 721.6.2(2)
Wood Structural Members
(2006 & 2009 IBC)
Membranes on Exterior Face of Walls • IBC Table 721.6.2(3)
SheathingpaperLumber siding: orWood shakes & shingles1/4" external grade plywood1/4" hardboardMetal sidingStucco on metal lathMasonry veneer
None None3/8" external grade plywood
Sheathing Paper Exterior Finish
Component Additive Method
For an exterior wall with a fire separation distance greater than 5 feet
(2006 & 2009 IBC)
Assume a 1 hour rated wall is required. A 2x4 stud wall has 20 minutes of resistance 5/8” Type X has a capacity of 40 minutes Note: Fire is assumed to be from one side of the wall.
Sample 1: Component Additive Analysis
(2006 & 2009 IBC)
Assume a 1 hour rated wall is required. A 2x4 stud wall has 20 minutes of resistance A single layer of ½” is insufficient Adding an additional layer of 1/2” Type X will give a one hour wall.
Sample 2: Component Additive Analysis
(2006 & 2009 IBC)
Assigned Times for Insulation of Cavity • IBC Table 721.6.2(5)
Mineral wool batts 15
Insulation Type Time (minutes
Component Additive Method
(2006 & 2009 IBC)
Assume a 1 hour rated wall is required. In lieu of the single ½” layer mineral wool batt insulation may be utilized.
Sample 3: Component Additive Analysis
(2006 & 2009 IBC)
FIRE-RESISTIVE EXPOSED WOOD MEMBERS
(2006 & 2009 IBC)
DCA 2: E-119 Fire Test
Beam Fire Test
DCA 2: Charred Cross-section
Beam Fire Design
D
W
Char layer
Heated Zone
Inner Zone
Detail 2 - Type III Platform Framing
No Scale
FRTW typ.
FRTW typ.
I-Joist
Sawn Lumber
1-hr. Assembly
1-hr. Assembly
2-hr wall Assembly 2-hr wall
Assembly A B
Detail 3 - Type III Semi-balloon Framing
No Scale
FRTW typ.
Sawn Lumber
1-hr. Assembly
2-hr wall Assembly A
FRTW typ.
Sawn Lumber
1-hr. Assembly
2-hr wall Assembly B
(2006 IBC)
Detail 4 - Type III Semi-balloon Framing
No Scale
Open web trusses
2-hr wall Assembly
A
1-hr. Assembly
FRTW typ.
Open web trusses
1-hr. Assembly
2-hr wall Assembly
B
Fire Walls
705.1 General - Each portion of a building separated by one or more fire walls that comply with the provisions of this section shall be considered a separate building. For example if an 18,000 sf building is desired using type VB the maximum square footage is 9,000sf.
Why incorporate fire walls
9,000sf
Max Size Type VB Max Size Type VB w/firewall
9,000sf 9,000sf
A Fire Wall effectively defines the boundaries for a new building. In many cases 2 hour walls are acceptable for Type V construction with untreated wood.
Fire Walls
• 705.6 Vertical continuity - Fire walls shall extend from the foundation to a termination point at least 30 inches (762 mm) above both adjacent roofs.
• 4. In Type III, IV and V walls shall be permitted to terminate at the underside of combustible roof sheathing or decks provided: • The roof sheathing or deck is constructed of fire-
retardant-treated wood for a distance of 4 feet.
Fire Walls – Continuous to roof
Design techniques and IBC code requirements
2 hr UL no. U336 GA file no. ASW
1000
Fire Wall:
Fire Walls – Vertical Continuity
Fire Retardant Treated Plywood
4’ 4’
• 705.5 Horizontal continuity. • Fire walls shall be continuous from exterior
wall to exterior wall and shall extend 18” beyond the exterior surface of exterior walls.
• Exceptions: Permitted to terminate at the interior surface of combustible exterior sheathing provided the exterior wall has a 1 hour rating for a horizontal distance of at least 4 ft on both sides of the fire wall.
Fire Walls – Continuous to ext. walls Fire Walls – Horizontal Continuity
18”
4’
4’
2 Hour Fire Wall
One hour fire rated wall 4’ both sides
2 hour wall penetrating through exterior wall.
Exterior Wall – WSP Sheathing
Interior Building
Interior Building Plan View
No need for protecting the outlets.
USG Shaft Wall at Tenant Separation
Construction Considerations
IBC 2009 Shrinkage
2304.3.3 Shrinkage. Wood walls and bearing partitions shall not support more than two floors and a roof unless an analysis satisfactory to the building official shows that shrinkage of the wood framing will not have adverse effects on the structure or any plumbing, electrical or mechanical systems, or other equipment installed therein due to excessive shrinkage or differential movements caused by shrinkage. The analysis shall also show that the roof drainage system and the foregoing systems or equipment will not be adversely affected or, as an alternative, such systems shall be designed to accommodate the differential shrinkage or movements.
Key Factors Influencing Magnitude of Shrinkage
Pre-construction moisture content (MC), vs. the in-service EMC Cumulative thickness of cross-grain wood contributing to shrinkage Wood species has relatively little impact since most species used in commercial construction have similar shrinkage properties.
Moisture Changes In Wood
Causes dimensional changes perpendicular to grain
Growing tree is filled with water
As wood dries,it shrinks perp. to grain
Wood Shrinks
Wood Shrinks
Woodmagazine.com
Wood only shrinks perpendicular to grain. (Shrinkage parallel to grain is approximately 1/40 of the shrinkage perpendicular to grain and can be neglected.)
The amount of shrinkage (or expansion) in wood is directly proportional to the change in moisture content.
The higher the moisture content at time of construction, the more shrinkage that can occur in the structure.
Wood Shrinks
Woodmagazine.com
Zone of Movement
Shrinkage occurs primarily in horizontal members such as wall plates and floor joists PLATES.
Shrinkage
Primarily in horizontal members such as wall plates and floor joists.
Moisture Content
19% 28%
Moisture Content
19% 28%
Indoors stabilize at 8-14% MC
Outdoors at 12-18% MC
Average Outdoor and Indoor EMC
(2006 IBC)
Construction Calculating Shrinkage
(2006 IBC)
Construction Considerations: • Sequencing • Framing • Finishes
Midrise Construction Sequencing
Common Methods (Type III) All Wood Framed
Hotels, Apartments, Condominiums
Wood Framed over Podium Mixed Use with Retail, Restaurant, or
Parking Below
Regardless of construction method, recognizing and addressing wood shrinkage is the key to successfully combining other building materials. Enclosed framing and mechanical systems will reduce moisture content in wood components, causing shrinkage.
Site and Framing Timeline Guidelines
Minimize storage of material on site where rain and standing water can increase moisture content.
Avoid framing on damp or rainy days. Schedule to avoid delays that will leave framing exposed to weather.
Keep unused framing material covered, especially at night when relative humidity increases.
Inspect pre-built wall panels prior to installation for proper material and quality of mechanical fasteners.
“Dry-in” the structure as quickly as possible. Immediately remove any standing water from floor
framing after rain showers.
Wrap-Around Construction
Often referred to as a “Texas Donut”, parking decks encircled by midrise construction can enhance security, safety, and the overall feel of a project.
OVERVIEW:
Key factors influencing the magnitude of wood frame shrinkage are: Pre-construction moisture content (MC) will typically be higher than equilibrium (in-service) moisture content (EMC) For example: MC 19% or 15% kiln-dried for commercial construction vs. in-service 8-10%. Wood species has relatively little impact since most species used in commercial construction have similar shrinkage properties.
OVERVIEW:
Key factors influencing the magnitude of wood frame shrinkage are (cont.): "settling" or "settlement of construction gaps“ or “framing take-up” 1/8 inch per floor ½ to ¾ inch total at the top floor of a high-rise
"creep" (long term movement under sustained loading) 1/8 to ¼ inch per story with magnitude progressively increasing from lower to upper stories).
Framing Tips
Effective way to detail the project to reduce cumulative shrinkage: • Minimize the cumulative width/depth of
wood framing members subject to (cross-grain) shrinkage
• Specify material less subject to shrinkage • Utilize kiln dried lumber with a maximum
moisture content of KD-14 or less, including treated wood.
Framing Tips Mitigate shrinkage:
• Avoid plates and fillers • Pressure-treated wood or engineered wood • Single top plates • Kiln dried top plates • For platform framing -engineered wood
framing such as I-joists or engineered open web trusses
Floor System Selection to Minimize Shrinkage
Avoid traditional platform framing with dimensional lumber or bottom chord bearing plated trusses. Shrinkage perpendicular to grain from full 30% moisture content to completely dry is between 2% - 13%. In contrast, shrinkage parallel to grain (along length of stud) is only 0.1% - 0.2%
Detail 1 - Type V Framing
No Scale
A B C
Engineered Wood Components
Cross-banding limits shrinkage/ warp
Efficient and Economical
Floor System Selection to Minimize Shrinkage
Structural Composite and I-Joist floor systems are dimensionally stable and offer reduced inter-floor shrinkage while utilizing traditional wall framing methods.
Floor System Selection to Minimize Shrinkage
Top chord bearing plated trusses minimize the inter-floor framing shrinkage in the wall system due to the reduced height of cross grain wood within the walls system. The use of a top mount hanger also minimizes inter-floor shrinkage and allows the use of dimensional lumber or bottom chord bearing plated trusses
Detailing Tips Mitigate shrinkage:
• Avoid plates and fillers • Pressure-treated wood or engineered wood • Single top plates • Kiln dried top plates • For platform framing -engineered wood
framing such as I-joists or engineered open web trusses
• Semi-balloon framing-hang floor framing off top-plates
Floor System Selection to Minimize Shrinkage
Balloon framing is an alternate framing style that minimizes inter-floor shrinkage from the wall assembly but is limited in height. Complicated connections and limited floor loads typically make balloon framing unusable in projects over 2 stories in height.
Detail 2 - Type III Platform Framing
No Scale
FRTW typ.
FRTW typ.
I-Joist
Sawn Lumber
1-hr. Assembly
1-hr. Assembly
2-hr wall Assembly 2-hr wall
Assembly A B
Diagrams courtesy of Simpson Strong-Tie
Top Flange Joist Hanger Installed over single 5/8” sheetrock layer flush with top of wall (drywall may be dropped max. ¾” with reduced loads) Detail 3 - Type III Semi-balloon Framing
No Scale
FRTW typ.
Sawn Lumber
1-hr. Assembly
2-hr wall Assembly A
FRTW typ.
Sawn Lumber
1-hr. Assembly
2-hr wall Assembly B
Differential Movement in Trusses
Drywall Clips & Slotted Anchor on Non-Bearing Wall www.sbcaindustry.com
DESIGN CONSIDERATIONS
Differential Movement at Balconies Multi-Story Wood-Frame Shrinkage Effects on Exterior Deck Drainage: A Case Study by Zeno Martin, Wood Design Focus Fall 2010
Mitigate distress to finishes arising from cumulative differential movement: • Be acutely aware of the fact that there
will be differential movement • Address detailing and specifications • Consider where distress will occur • Provide details to relieve or avoid it.
Mixed Materials
The important thing to recognize is that cumulative shrinkage is the issue - not absolute values per floor or story. This is especially of interest when considering differential movement between wood frame elements and other materials, especially those that:
1) do not shrink at all (steel framing or steel/cast iron piping, such as plumbing stacks), or
2) shrink much less (concrete masonry, such as is often used in stair and elevator shafts), or
3) worst of all, materials that actually expand, such as brick commonly used in veneers for facility types for which high-rise wood frame construction is often used. Like wood shrinkage, brick growth (and issues relative to differential movement with wood framing) is well addressed in the literature. See Brick Institute of America’s (BIA) Tek Note #18 covers the analysis and effects of movement.
Detailing Tips
Classic conditions: Windows in exterior walls - Such windows often serve as the bridge between shrinking wood frame and growing brick veneer. BIA Tek Note 18A, Accommodating Expansion of Brickwork, also points to the need for expansion joints (soft joints) around windows (and doors) projecting into the veneer. Floor framing interfacing with unyielding materials or components - Such materials
Site and Framing – Timing Guidelines
Fully compress wall framing by completing all dead load potential. Complete all interior wall framing, roof framing, sheathing, floor toppings and roofing PRIOR to brick or stucco work.
Allow for differential movement
in tall wood frame buildings.
Site and Framing – Timing Guidelines
Fully compress wall framing by completing all dead load potential PRIOR to mechanical installations. Avoid rigid vertical piping in mechanical and plumbing systems. Flexible members allow for shrinkage between floors.
Site and Framing – Timing Guidelines
Vertical vent stacks should not be installed prior to full completion of framing. Vent stacks require special attention and must be designed to allow for vertical movement due to shrinkage between floors.
Addressing Sound Concerns
Sound Transmission Class (or STC) is an integer rating of how well a building partition attenuates airborne sound. In the USA, it is widely used to rate interior partitions, ceilings/floors, doors, windows and exterior wall configurations (see ASTM International Classification E413 and E90).
The STC number is roughly the reduction in decibels that a partition creates in the 125 Hz to 4,000 Hz range..
Example - If an 80dB sound on one side of a wall/floor/ceiling is reduced to 50dB on the other side, that partition is said to have an STC of 30
IBC Sound Requirements
1207.2 Air-borne sound: Walls, partitions and floor/ceiling assemblies separating dwelling units from each other or from public or service areas shall have a sound transmission class (STC) of not less than 50 (45 if field tested) for air-borne noise when tested in accordance with ASTM E 90.
1207.3 Structure-borne sound. Floor/ceiling assemblies between dwelling units or between a dwelling unit and a public or service area within the structure shall have an impact insulation class (IIC) rating of not less than 50 (45 if field tested) when tested in accordance with ASTM E 492.
Sound Transmission – Typical Floor Assembly
UL Des L528 STC RATING : 53 Carpet and pad 3/4" poured topping 3/4" plywood floor 12" wood truss, 24" o.c. resilient channel 16" o.c. 5/8" Type C Gypsum Panel
Floor/Ceiling sound transmission levels are easily addressed utilizing common methods. Most major gypsum, insulation, and truss/joist manufacturers maintain catalogs and calculators determine the materials required to satisfy appropriate STC ratings.
Sound Transmission – Typical Wall Assembly
STC Rating: 52 5/8" Type C Sheetrock 2x4 wood stud 16" or 24" o.c. 3" mineral wool batt resilient channel or equivalent one side joints finished
Sound Transmission – Typical Wall Assembly
STC Rating: 54 5/8" Type C Gypsum 2x4 non-loadbearing staggered wood stud 16" o.c. 2x3 plates 1" apart, panels fastened 7" o.c. 2" Sound absorbing fiber batt one side screws or nails 7" o.c.
American Wood Council on-line Heights and Areas calculator http://www.awc.org/calculators/IBCheightarea/IBCHeightArea.html American Wood Council online Course Fire Design Methodologies for Code Acceptance http://www.awc.org/HelpOutreach/eCourses/BCD201/BCD201eCourseV09-2007.pdf
Additional Information
For a 5 story sprinklered building; Using type IIIA; B, F-2, H-3, I-1, M, R, S-2. Offices, Assisted Living, Mercantile, and Residential
Common Examples Building Height
(2006 IBC) (2006 IBC)
For a 4 story sprinklered building; Using type IIIA; A, E, F-1, H-5, I-4. Examples include assembly areas, and schools.
Common Examples Building Height
(2006 IBC)
Hospitality Moves to Wood
Hotel Construction - early 1990’s Traditionally Concrete and
Masonry (2006 IBC)
Mixed Use & Retail Retail on Lower Level (concrete) – with 3-5 Stories of Retail and Living Units Above
