At the Structural Insulated Panel Association (SIPA), our mission has always been to back innovative building practices with solid, technical evidence. We're excited to share the results of an innovative, multiyear study that strengthens this mission: demonstrating that Structural Insulated Panels (SIPs) not only match but may even surpass traditional wood-framed roofing systems in terms of long-term durability and resistance to deflection—commonly referred to as “creep.”
A Collaborative Effort in Research
This extensive research was a joint effort between the U.S. Department of Agriculture’s Forest Product Laboratory (FPL) in Madison, Wisconsin, Mississippi State University’s PhD Engineering Program, and SIPA. Our collective aim was to investigate the long-term performance of SIPs under sustained loads, simulating conditions like snow buildup or the weight of rooftop equipment.
Understanding Creep and Load Testing
When structural engineers design roofing systems, one key concern is how these systems hold up over time under pressure—a behavior known as “creep.” In traditional wood framing, long-term loads can cause sagging, bending, or bowing. This study sought to measure whether SIPs behave similarly or better than their conventional counterparts.
The research spanned 90 days, during which SIP panels were meticulously tested under various loads. Measurements were taken to record deflection levels, and researchers closely observed if the panels would “spring back” to their original shape once the load was removed.
Key Findings: SIPs Hold Their Own
The findings are significant. The study concluded that both 6.5-inch and 12.25-inch SIP panels met the acceptance criteria specified in ASTM D6815, a standard used for assessing the duration of load and creep effects on wood-based construction materials.
Deflection Measurements: The 6.5-inch SIPs exhibited deflection between 0.27 and 0.50 inches, while the 12.25-inch SIPs ranged from 0.41 to 0.66 inches. These values were well within acceptable limits.
Compliance with Industry Standards: SIPs manufactured to ICC-ESR 4689 – the common industry code report representing ten SIP manufacturers in North America – were confirmed to perform as required by ASTM D6815: Standard Specification for Evaluation of Duration of Load and Creep effects of Wood and Wood-Based Products, reinforcing their reliability in load-bearing roofing applications.
>>Final Phase 3 Report: Evaluation of Creep Performance of Structural Insulated Panels (SIPs): Confirmation that SIPs have creep characteristics consistent with traditional solid wood and lumber construction
>>FPL Journal SIP Creep Summary: Overview of the aspects of the study related to the EPS foamBuilding Trust Through Evidence
For architects, structural engineers, and building code officials, these results provide an added layer of assurance in the strength and reliability of SIPs for critical construction projects. This research highlights SIP technology's resilience and reinforces SIPA’s role in advancing sustainable and efficient building practices.
These findings mark a significant milestone in our ongoing commitment to research and innovation. By demonstrating the durability and versatility of SIPs, this study proves that our panels are not just a modern building solution but a dependable and forward-thinking choice for the future of construction.
Dive Into the Research
We invite you to explore the details of these reports and see the science for yourself. All technical reports of this multiyear study are available on our Technical Research Resource Library. The research outcomes mark an important step, reaffirming that SIPs are engineered for lasting performance and ready to redefine how we think about building strength.
2024 - FPL Journal Summary SIP Creep Article
2024 - FPL Final Phase 3 SIP Creep Report
Creep Behavior of SIPs Under Load
Flexural Testing of SIPs Before & After Creep Testing
Creep Performance of SIPs Phase 2
Creep Behavior of SIPs Pilot Study
