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


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.


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.


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.



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



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.



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.


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.



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.



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


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.


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.


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.


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.


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.


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


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


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.


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


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.


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).



• 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.



• 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.


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.



• 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.



• 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.



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



• 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.



• 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.



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.



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


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


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



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



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




• 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




• 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



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





• 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





• 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



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



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




• 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




• 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



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



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



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.

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

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