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Engineered Design of Structural Insulated Panels (SIPs)

Mike J. Nelson, P.E., S.E.


Course Outline

This 11 hour online course covers current SIP Acceptance Criteria for SIPs, provides a sample code evaluation report, describes early numerical strength analysis methods, compares these early methods with current finite element methods along with modified versions of early methods intended for ease of use in a design office environment by practicing engineers.  Seismic issues are discussed, along with concerns and solutions for SIP use in high seismic areas.

This course includes a multiple choice quiz at the end, which is designed to enhance the understanding of the course materials.

Learning Objective

At the conclusion of this course, the student will be familiar with:

Intended Audience

This course is intended for structural engineers, architects and building code officials

Benefit to Attendees

Attendee of this course will be acquire an understanding of engineering issues involving SIPs that will produce needed confidence in designing with them.

Course Introduction

Structural Insulated Panels are relatively unknown in the engineering and architectural community.  As their use gains in popularity, design professional will encounter opportunities to work with this product.  It’s important to have a basic understanding of engineering design issues in order to make proper use of SIPs.  Having this understanding should raise the comfort level among engineers, architects and building officials when SIPs are being considered.

Course Content

The following discussion contains underlined blue hyperlinks to relevant literature that discusses engineered design of structural insulated panels (SIPs).  This literature collection represents the bulk of the course, and information in all pieces of literature will be included in the quiz..

Structural Insulated Panels were approved for prescriptive use in the 2007 supplement to the 2006 International Residential Code.  However, structures not meeting the requirements of the IRC require an engineered design.

Over the years, engineered design of structural insulated panels has relied heavily on proprietary code reports containing strength testing data. 

The SIP testing process typically involves 3rd party product testing, evaluation, and certification by either ICC Evaluation Services, or Product Certification Agencies (PCAs), like NTA, Inc.

ICC-ES has developed a testing criteria: ICC-ES Acceptance Criteria for Sandwich Panels - AC04 that is widely recognized and adhered to in the SIP industry.

The results of the testing are then processed into an Evaluation Report or Product Certification Report.  Click Sample Code Report for an example.

Proper and thorough panel testing is both expensive and time consuming for manufacturer’s and creates a barrier to entry for new manufacturers.

To address this situation much work has been done over the years to develop “manual” calculation methods that engineers can use for those structures that do not comply with the prescriptive SIP requirements of the International Residential Code (IRC) or International Building Code (IBC).

Early work in 1990 was done by the American Plywood Association, whose results can be found in their Supplement #4 : Design & Fabrication of Plywood Sandwich Panels.

Subsequent comparisons with actual test data, however, revealed poor load/deflection predictive ability of the APA methods.

College thesis work, completed in 2002 by Heming Zhang Alwin, developed an alternative, finite element computational method to further compare with results predicted by APA method.   Significant differences were discovered.  The thesis, titled "Development of a Method to Analyze Structural Insulated Panels Under Transverse Loading” provides valuable insight into SIP behavior.

More recently, the Product Certification Agency,  NTA, Inc., using their vast database of test results, have come up with modifications to the APA method using basic SIP property information that was previously unavailable.   The modified APA method more accurately predicts actual SIP behavior. Click Beyond Code Reports: Taking SIPs from Data to Design and Engineered Design of SIP Panels using NTA Listing Report Data for a summary of their work.  The use of analysis equations under the NTA method still depends on testing to derive basic SIP properties.  Engineers using the NTA methods should check with the manufacturer for NTA Product Certfication Report to obtain basic property information, if available.

Most of the smaller SIP manufacturer’s do not have NTA Product Certification Reports, which is expensive and time consuming to obtain. 

The question engineers inevitably will ask is: “Can the basic property information taken from a particular manufacturer’s code evaluation report can be used for other manufacturer’s SIPs that do not have a code evaluation report report, as long as the materials and fabrication processes are identical ? 

In theory, the answer should be “yes”.  However, large differences in test results between different manufacturer’s using identical or nearly identical materials suggest wide variations in quality control measures during fabrication.

Also, the use of identical materials and processes, as well as quality control measures, would require some type of documented evidence acceptable to both the engineer and building departments. In some cases, a manufacturer will purchase a code evaluation report from another manufacturer and pay a product certification company to assess and document compliance as to the use of equivalent materials, fabrication and quality control.

SIPs are a non-homogeneous material that will always rely on some level of testing, which in turn creates proprietary issues used to business advantage in a competitive marketplace.   In the end, after consideration of technical, ethical and liability issues, it’s up to the engineer’s judgment and the judgment the building official checking the plans.  SIPs remain relatively unknown to many building departments.  Having convincing load capacity documentation for a specific manufacturer is often required by a plan checker unfamiliar with SIPs.

 This white paper titled: Analysis of the Seismic Performance of SIPS, sponsored by the American Society of Civil Engineers, discusses code limitations regarding seismic design and the importance of achieving building code of acceptance of SIPs in high seismic areas. It provides a good description of the role of the International Code Counsel Evaluation Service and Produce Certification Agencies like NTA, Inc. in achieving this acceptance.   The paper goes on to discuss SIP behavior under cyclical seismic induced. 

Please click on the above underlined hypertext to view, download or print the document for your study. Because of the large file size, we recommend that you first save the file to your computer by right clicking the mouse and choosing "Save Target As ...", and then open the file in Adobe Acrobat Reader. If you still experience any difficulty in downloading or opening this file, you may need to close some applications or reboot your computer to free up some memory.
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Course Summary

This course is a collection of articles and technical literature designed to create a foundation of understanding of the structural engineering issues involving structural insulated panels over the years.  It will provide the student with knowledge of strength evaluation methods that compare testing methodologies with numerical methods.  The material also discusses the role of code evaluation reports and the organizations that create the reports, along with a description of obstacles and progress toward gaining acceptance by building codes for the use of SIPs in high seismic areas.  Calculation methods are presented that will allow the student to “manually” calculate the strength of SIPs for use in design, instead of reliance on often times limited test data.

Related Links

For additional technical information related to this subject, please visit the following websites:

Structural Insulated Panel Association  

Quiz

Once you finish studying the above course content, you need to take a quiz to obtain the PDH credits.

Take a Quiz

DISCLAIMER: The materials contained in the online course are not intended as a representation or warranty on the part of PDH Center or any other person/organization named herein. The materials are for general information only. They are not a substitute for competent professional advice. Application of this information to a specific project should be reviewed by a registered architect and/or professional engineer/surveyor. Anyone making use of the information set forth herein does so at their own risk and assumes any and all resulting liability arising therefrom.