Designing Floor Systems with Engineered Wood Joists - Ron Blank ...

© Ron Blank & Associates, Inc. 2009
Designing Floor Systems
with Engineered Wood Joists
An AIA Continuing Education Program
Course Sponsor
Universal
Forest Products, Inc.
2801 East Beltline NE
Grand Rapids, MI 49525
616-365-6608
E-mail
cfox@ufpi.com
Web
www.ufpi.com
Course Number
ufp06a
Designing Floor Systems with Engineered Wood Joists
Please note: you will need to complete the conclusion
quiz online at ronblank.com to receive credit
Credit for this course is 1 AIA HSW CE Hour
©2007 Universal Forest Products. The material contained in this course was researched, assembled, and produced by Universal Forest
Products and remains their property. Questions or concerns about the content of this course should be directed to lkroh@ufpi.com.

An American Institute of Architects (AIA)
Continuing Education program
Approved Promotional Statement:
Ron Blank & Associates, Inc. is a registered provider with The American
Institute of Architects Continuing Education System. Credit earned upon
completion of this program will be reported to CES Records for AIA members.
Certificates of Completion are available for all course participants upon
completion of the course conclusion quiz with +80%.
Please view the following slide for more information on Certificates of
Completion through RBA
This program is registered with the 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 or Ron Blank & Associates, Inc. of
any material of construction or any method or manner of handling, using,
distributing, or dealing in any material or product.

An American Institute of Architects (AIA)
Continuing Education program
• Course Format: This is a structured, web-based, self study course with a
final exam.
• Course Credit: 1 AIA Health Safety & Welfare (HSW) CE Hour
• Completion Certificate: A confirmation is sent to you by email and you can
print one upon successful completion of a course or from your
RonBlank.com transcript. If you have any difficulties printing or receiving
your Certificate please send requests to certificate@ronblank.com
Design professionals, please remember to print or save your certificate of
completion after successfully completing a course conclusion quiz. Email
confirmations will be sent to the email address you have provided in your
RonBlank.com account.
Please note: you will need to complete the conclusion quiz
online at ronblank.com to receive credit

Course Description
There are many factors to consider when designing a floor system
with engineered wood joists. Review the design strategies, code
requirements, different types of engineered floor components, and
their capabilities and limitations.

Course Objectives
Upon completion of this course the design professional will be able to:
List the factors to consider when designing floor systems
Explain the appropriate design strategies for code requirements and client
satisfaction
List the types of engineered floor components, their capabilities, and
limitations
Explain the Engineering, design, and support available from manufacturers

The advent of engineered wood framing
components has impacted floor system and
subsequent building design
Engineered products use wood fiber more efficiently and permit the use of
former “waste” fiber for new structural components with greater strength than
solid sawn lumber.
New configurations with “I” shapes and triangles result in products with greater
strength than solid sawn lumber.
Because of this new strength, design
professionals now have greater design
flexibility and opportunities for designing
larger open spaces.
This new strength also produces new
construction efficiencies through fewer
components and faster installation.

Impact of Engineered Wood
on Floor System Design
Designing floor systems
with engineered wood
components requires new
considerations by design
professionals.
In addition to “safety”
considerations addressed
by the model building
codes, “user comfort” and
system performance with
regard to deflection,
vibration and sound
transfer must now become
integral factors in
designing floor systems.

Designing floor systems with engineered wood
products requires attention to three sets of
considerations:
1. Requirements of the applicable model building code with
regard to “safety” factors.
2. Practical considerations including product availability, ease and
speed of installation, and design flexibility.
3. “Comfort” factors that may have impact on the physical and
psychological well-being of those who will occupy or visit a
building.
Let’s look at the various design considerations within each of
these categories.

Design Considerations:
Building Code Requirements
Design Safety Factors:
• Length of Span
• Loading Conditions
• Deflection Criteria
• Joist Spacing
• Fire Endurance
• Seismic Performance
• Local Regulations

Building Code Requirements
Safety Factor: Length of Joist Span
Length of span, while not specified by the building codes, is certified and
published by joist and truss manufacturers and is recognized by the model
building codes in product evaluation reports. Published spans may be used
by design professionals within the specified loading and spacing
parameters.

Building Code Requirements
Safety Factor: Length of Joist Span
Length of the joist span is determined by the designer’s space concepts
and the locations of bearing points in a structure. Designers often
relocate bearings to accommodate span capabilities.
Once a desired span has been identified, it must be considered in context
with loading conditions, deflection characteristics, joist spacing and
bearing size.
Consult manufacturers’ literature and software to confirm the appropriate
joist span for given conditions.

Building Code Requirements
Safety Factor: Loading Conditions
Three types of loads may apply to any floor system:
• Live Loads
• Dead Loads
• Special Loads (Line, Point, Area)
Live Loads are temporary loads and are defined by the building codes
according to the intended use of the structure.
Dead Loads are permanent loads and are comprised of the actual
weights of materials that make up the floor/ceiling system.
Special Loads are permanent and are actual design loads occurring on
confined areas of a floor system.

Building Code Requirements
Safety Factor: Loading Conditions
Live Loads:
Live Load conditions consider temporary loads uniformly
applied to the floor system (people, furniture and moveable
items) and are specified by the building codes according to the
designated function of the space, i.e.:
• Residential Living Spaces: 40 PSF
• Office Use: 50 PSF
• Retail Use: 80 PSF
• Assembly Areas: 100 PSF

Building Code Requirements
Safety Factor: Loading Conditions
Dead Loads:
Dead Loads are permanent, non-moveable elements (floor framing and
decking, ceiling finish, mechanical systems, insulation, etc.) and loading is
determined by the sum of the weights…per square foot…of all these
elements. Dead Loads are applied uniformly to the floor system.
Common design practice uses standard Dead Load factors of 10, 15 or 25
PSF depending on the makeup of the floor/ceiling envelope.

Building Code Requirements
Safety Factor: Loading Conditions
Special Loads:
Line, Point and Area Loads are permanent and represent concentrated
loads on specific limited areas of a floor system. They are not applied
uniformly. These special loads may result from roof framing, interior bearing
walls, large mechanical units, large fixtures, etc.

Building Code Requirements
Safety Factor: Deflection
Deflection is vertical movement of a floor system when subjected to loads.
The Building Code specifies Deflection Limits for floor systems:
L/360 Live Load Deflection and L/240 Total Load Deflection
(“L” is joist length in inches)
Example:
Joist Length of 20’ (L= 240)
240 divided by 360 = .67 inches allowable deflection under full load
condition
Deflection limits are based on historical performance and are specified by
the codes for user comfort and to prevent cracking of ceiling and flooring
materials.

Building Code Requirements
Safety Factor: Deflection
Deflection performance of a floor system is determined by three factors:
• Length of Joist Span
• Loading Conditions
• Stiffness of the Framing Member (joist)
Of these three, Length of Joist Span has the greatest impact on deflection.

Building Code Requirements
Safety Factor: Deflection
Floor system deflection can be reduced in several ways:
• By reducing Loading (by decreasing the on-center spacing of the joists)
• By reducing the Joist Span
• By increasing the Joist Depth
• By upgrading Joist size or materials:
• Larger dimension flange or chord
• Higher lumber grade of components
• Use of engineered materials

Building Code Requirements
Safety Factor: Joist Spacing
The building code does not specify on-center joist spacing but does require
spacing that will produce specified deflection performance for the loading
conditions.
Joist spacing is most often determined by owner/builder preference or the
desire to “value engineer” the floor system.
Traditional joist spacing is 16” o.c.
Stronger engineered joists have made possible new on-center spacing
options of 19.2” and 24”.
The building codes set only minimum requirements for floor system
performance.
Value engineering recognizes the ability of fewer, stronger joists to meet
code minimums.

Building Code Requirements
Safety Factor: Joist Spacing
Joist spacing must be considered along with loading conditions and length of
span when designing to achieve desired deflection performance.
Floor system performance may be enhanced by designing for higher
deflection limitations, especially for longer spans.
Since loading conditions and length of span cannot normally be changed,
Joist Spacing is the element most often changed to achieve desired
deflection performance.

Building Code Requirements
Safety Factor: Fire Resistance
Building classification and building codes determine if floor systems must be
designed to meet minimum fire resistance requirements.
Multi-Family and institutional residences most often require separation of
living units by fire resistant floor/ceiling assemblies.
Single-Family residences with integral garages often require separation.

Building Code Requirements
Safety Factor: Fire Resistance
Minimum standards for fire endurance are specified by building codes to
allow adequate time for building occupants to escape during a fire and for
firefighters to extinguish fires.
Floor/ceiling assemblies are designed to endure in a fire for a specified
duration of time…one, two, or more hours (depending on the code
requirement).
Assemblies are tested for fire endurance by independent third-party testing
agencies using ASTM standard test designs and procedures.
Once certified, endurance assemblies are published by component product
manufacturers and by certification agencies.

Building Code Requirements
Safety Factor: Seismic Performance
Individual floor joists cannot be rated for a
specific seismic zone since they only act as
components of a lateral-force-resisting
system.
Joists act as “drag struts” or “chords” in
lateral-force-resisting systems such as shear
walls.
Designers must be aware of the required
forces a drag strut must carry and refer to
manufacturer data for the product’s drag
strut capabilities.
Drag Loads are normally specified by the
building designer on construction plans.

Building Code Requirements: Local Regulations
A few local jurisdictions prohibit the use of specific engineered wood framing
products.
Some local codes specify more stringent deflection limitations for floor
systems than the model building codes permit.
Some municipalities have fire protection regulations requiring the use of
sprinkler systems and/or baffling in floor systems. Fire endurance
requirements may also vary by jurisdiction.
Design professionals must be
aware of these local regulations
when designing engineered wood
floor systems.

Building Code Requirements
Because SAFETY is the primary purpose of model building code
enforcement, adherence to code requirements is the responsibility of all
the following:
• Design Professionals
• Project Developer
• General Contractor
• Framing Contractor
• Mechanical Trades
• Building Inspector

Design Considerations: Logistical Factors
Several elements of practicality must be considered when choosing the type
of framing product to be used in an engineered wood floor system, including:
• Installation of Mechanical Systems
• Construction Timetable
• Product Access
• Cost

Design Considerations: Logistical Factors
Installation of Mechanical Systems
Electrical, Plumbing, HVAC:
Is it necessary or desirable to contain mechanical
systems within the floor/ceiling envelope (due to building
height restrictions, basement headroom, etc.)
Is it necessary or desirable to frame bulkheads for duct
runs (may also be a design element)
Is the construction schedule impacted by mechanical
systems installation time
Is there likelihood of error when joists are altered to allow
mechanical systems penetrations
Do MEP requirements and fixture placement dictate joist
depth and spacing

Design Considerations: Logistical Factors
Construction Timetable:
Will floor framing materials be shipped on a schedule to conform with job
site progress
Is it reasonable to expect timely and efficient installation of floor system
components
The pace of construction obviously
impacts project cost.

Design Considerations: Logistical Factors
Product Access:
Are there dependable local sources
of supply for engineered wood
products
Do suppliers offer competent
technical support for the
engineered products they offer
Is there confidence that supply
issues will not result in “down time”
at the job site

Design Considerations: Logistical Factors
Cost:
Installing the strongest, best performing
floor system for the lowest cost is
everyone’s natural objective.
The installed cost of a system that meets
both structural and performance
requirements is the standard of
measurement used to judge the success of
a floor system design.

Design Considerations: Comfort and Performance
Two floor system factors have significant physical and psychological impact
on individuals who inhabit or use a building. Those factors are:
Sound Transmission &
Floor Vibration
While these factors may, in fact, be measured quantitatively, reactions to
them by humans are purely subjective. For this reason, design
professionals should be aware of human preferences for performance with
regard to these factors.

Design Considerations: Comfort and Performance
Sound Transmission:
• Sound transmission refers to how easily sound is transferred through
an elevated floor system.
• Some code bodies set requirements for sound performance by
specifying minimum standards for Sound Transmission Class (STC)
and Impact Insulation Class (IIC).

Design Considerations: Comfort and Performance
Sound Transmission:
• STC and IIC ratings are determined by the testing and certification of
floor/ceiling assemblies by independent third-party agencies.
• Codes and designers specify minimum STC and IIC ratings for floor
systems to satisfy the majority of people who occupy or use a
structure.
• It remains a fact that human reactions to sound transmission are totally
subjective in nature.

Design Considerations: Comfort and Performance
Sound Transmission:
• Manufacturers of engineered wood floor framing components and thirdparty
agencies publish sound performance assemblies for reference by
designers.
• To maintain sound performance requirements, construction details
must be followed accurately so that assemblies are not compromised
by penetrations, etc.

Design Considerations: Comfort and Performance
Floor System Vibration:
• Vibration is oscillatory movement of the floor system when subjected to a
live load such as footsteps, a dropped item, or machine vibration.
• Floor vibration performance is the least quantitative and most subjective
characteristic of a floor system.
• Vibration performance should be a priority.
• consideration for floor system designers.

Design Considerations: Comfort and Performance
Floor System Vibration:
• Studies have shown that excessive floor system vibration makes
occupants uncomfortable and may even cause them to fear system
failure.
• It is also known that auditory effects (rattling china closets, etc.)
heighten human discomfort with vibration.
• Vibration is not necessarily related to the structural integrity of a floor
system and extra design measures may be required in anticipation of
satisfying end users.

Design Considerations: Comfort and Performance
Floor System Vibration:
• It should be recognized that floor system vibration is a performance
concern, not a safety issue.
• U.S. building codes do not specify vibration performance requirements for
floor systems.
• It should also be recognized that vibration is not simply a side effect of
deflection.

Design Considerations: Comfort and Performance
Floor System Vibration:
Three factors influence human response to floor system vibration:
• The Frequency Content of the vibration
• The Amplitude of the vibration
• The effects of vibration Damping

Design Considerations: Comfort and Performance
Floor System Vibration:
• Frequency Content is the cycle time of the vibration, measured in
cycles per second or hertz, Hz.
• Humans feel more comfort with higher frequency vibrations than
lower Hz cycles.
• Shorter lengths of span have higher frequencies than long lengths of
span.

Design Considerations: Comfort and Performance
Floor System Vibration:
• Amplitude is the magnitude of floor vibration.
• Amplitude is directly related to the stiffness of the floor (deflection).
• High amplitude vibrations are more annoying to people than low amplitude
vibrations.

Design Considerations: Comfort and Performance
Floor System Vibration:
Amplitude may be reduced by two methods:
• Specifying deeper framing members (joists)
• Using bridging between joists
• Continuous bridging perpendicular to the
bottom flange of the joist is the most effective.

Design Considerations: Comfort and Performance
Floor System Vibration:
Damping of vibration reduces amplitude and shortens the duration of
vibrations.
Damping is provided by existing loads and frictions within the floor system.
Damping is achieved with bridging and through the presence of interior
partition walls.

Design Strategies
To determine the proper design strategy for a project, the design
professional must consider building classification, safety factors, comfort
factors and cost.
These considerations will lead to
one of two basic design strategies:
• Code Minimum Strategy
• Client Satisfaction Strategy

Design Strategies
Code Minimum Strategy:
Most often, this strategy is identified as the
“Value Engineering” approach. In this design
strategy:
• On-center joist spacing is maximized and
long spans are accommodated
• Quantities of framing materials are
minimized and installation time is reduced
• The installed cost of the floor system is
minimized

Design Strategies
Client Satisfaction Strategy:
• The classification of a building normally
dictates the application of this strategy.
Custom residences and other privately
commissioned projects naturally demand
a client satisfaction design strategy.
• This strategy gives high priority to comfort
and performance factors when designing
floor systems and usually specifies
structural performance in excess of that
required by the building codes.
• In this strategy, cost is usually not of
primary concern.

Engineered Wood
Floor Framing Components
Now let’s consider the engineered wood floor framing components
available in today’s market.
They include:
• Floor Joists
• Beams and Girders
• Rim / Band Board
• Hangers / Connectors

Engineered Wood
Floor Framing Components
Floor Joists:
There are three types of engineered wood joists
available today:
• Wood I-Joists
• Steel-Plate-Connected Parallel Chord
Floor Trusses
• All-Wood Parallel Chord Floor Trusses

Engineered Wood
Floor Framing Components
Wood I-Joists:
• Invented 1969 by Truss Joist Corporation
• Extensive architect education effort
• “I” cross section
• Solid sawn flanges and plywood web
• Switched to LVL flanges and OSB webs in 1990’s
• APA-The Engineered Wood Association published standards for I-
Joists in 1990’s

Engineered Wood
Floor Framing Components
Wood I-Joists:
• Flanges resist bending, web resists shear
• Lighter than dimension lumber
• Efficient use of wood fiber
• Consistent quality
• Penetrations through web limited
• Depths of 9-1/2”, 11-7/8”, 14”, 16”, 18”
• Multiple span applications with proper blocking

Engineered Wood
Floor Framing Components
Wood I-Joists:
• Flange dimensions of 1-1/2” to 3-1/2”
• Flanges of solid sawn SPF, LVL, LSL
• Installation requires accessory
reinforcement pieces: web fillers, web
stiffeners, squash blocks
• Can accommodate some point, line and
area loads with proper reinforcement
• Structural rim board is required at ends of
joists
• Engineered repair details required

Engineered Wood
Floor Framing Components
Steel-Plate-Connected
Parallel Chord Floor Trusses:
• Invented in 1952 by A. Carroll Sanford
• Open web configuration
• Made possible by the innovation of
the steel truss plate
• Steel plate values are measurable
and can be sized to handle forces of
compression and tension at joints
• Truss engineering software is used to
design trusses for specific job
conditions

Engineered Wood
Floor Framing Components
Steel-Plate-Connected
Parallel Chord Floor Trusses:
• Constructed of SYP, Doug Fir or SPF lumber
• Flanges of 4x2 most common
• Web dimensions must be same as flange
dimension
• May be designed to accommodate duct
chases
• Must be fabricated to exact jobsite
dimensions
• Structural rim board is not required at ends of
trusses

Engineered Wood
Floor Framing Components
Steel-Plate-Connected
Parallel Chord Floor Trusses:
• Can be designed to handle point, line,
and area loads
• Common depths are 12”, 14”, 16”, 18”,
20”, 22”, 24”
• May be damaged by excessive
construction materials loads
• Engineered repair details required

Engineered Wood
Floor Framing Components
Proprietary Steel Plated
Floor Trusses:
• Open web configuration
• Wood or steel webs
• Stock lengths with trim-able “I” ends
• Space Joist TE, Trim Joist, Gator Joist
• Depths of 9-1/4”, 11-1/4”, 14”, 16”, 18”
• Flanges of 4x2 or 3x2
• Structural rim board required

Engineered Wood
Floor Framing Components
All Wood Parallel Chord Trusses:
• Invented in Canada in 1989
• First trim-able open-web floor joist
• Stock lengths in one-foot increments
• Combination of “I” and truss engineering
• Values from actual testing

Engineered Wood
Floor Framing Components
All Wood Parallel Chord Trusses:
• Assembled with precision finger joinery
and structural adhesive
• No metal plates or fasteners
• Spruce-Pine-Fir flanges and webs
• Flanges of 4x2 and 3x2
• Depths of 9-1/4”, 11-7/8”, 14” 16”
• Technology allows efficient use of wood
fiber

Engineered Wood
Floor Framing Components
All Wood Parallel Chord Trusses:
• Trusses are individually tested
• Standard repair details on hand
• Simple span installation
• Bottom-chord-bearing
• 1-1/2” bearing required
• Can accommodate point, line, and
area loads with proper
reinforcement
• Structural rim board not required

Engineered Wood
Floor Framing Components
Structural Rim Board:
Structural rim is designed to support vertical
loads transferring down through bearing walls.
This rim is available in several engineered wood
technologies, including:
• LVL (laminated veneer lumber)
• PSL (parallel strand lumber)
• LSL (laminated strand lumber)
• OSB (oriented strand board)
• Glu-Lam (laminated solid sawn lumber)
• Solid sawn lumber

Engineered Wood
Floor Framing Components
Beams and Girders:
Beams and girders are manufactured with the same technologies as
structural rim board, including:
• LVL (laminated veneer lumber)
• PSL (parallel strand lumber)
• Glu-Lam (laminated solid sawn lumber)
• Steel plated girder trusses

Engineered Wood
Floor Framing Components
Hangers and Connectors:
• The designer must choose
hangers that accommodate the
loads and reactions at the ends
of joists and beams.
• Major manufacturers offer
products to fit all engineered
wood joist and beam sizes.
• Manufacturers provide Design
Guides to help designers
choose correct products.

Design Assistance
Manufacturer Literature:
• Span charts and load tables
• Installation details
• Fire and sound assemblies
• Product specifications
Manufacturer Websites:
• Repeat of printed information
• Interactive for product sourcing
• Downloadable details and specs

Design Assistance
Engineering/Design Software:
• Usually offered free of charge by
manufacturer
• Training is usually provided
Design Done by Supplier:
• Design floor system to architect’s
specifications
• Final approval by architect and/or
engineer
• Sealed shop drawings should be
available from the manufacturer

Course Summary
The design professional will now be able to:
List the factors to consider when designing floor systems
Explain the appropriate design strategies for code requirements and client
satisfaction
List the types of engineered floor components along with their capabilities
and limitations
Explain the Engineering, design, and support available from manufacturers

© Ron Blank & Associates, Inc. 2009
Designing Floor Systems
with Engineered Wood Joists
An AIA Continuing Education Program
Course Sponsor
Universal
Forest Products, Inc.
2801 East Beltline NE
Grand Rapids, MI 49525
616-365-6608
E-mail
cfox@ufpi.com
Web
www.ufpi.com
Course Number
ufp06a
Designing Floor Systems with Engineered Wood Joists
Please note: you will need to complete the conclusion
quiz online at ronblank.com to receive credit
Credit for this course is 1 AIA HSW CE Hour
©2007 Universal Forest Products. The material contained in this course was researched, assembled, and produced by Universal Forest
Products and remains their property. Questions or concerns about the content of this course should be directed to lkroh@ufpi.com.