Best PracticesComposite Metal Hybrid (CMH)A2P1049: Understanding the Differences Between Fiber-Reinforced Polymer (FRP) and Best Practice Composite Metal Hybrid (CMH) Sub-Framing

May 23, 2023


Composite materials have been gaining popularity in various industries due to their design flexibility and thermal resistance. In the construction industry, composite materials have been especially advantageous because they provide an efficient solution to common structural challenges such as weight limitations, corrosion resistance, and long-term sustainability. Aside from traditional metal-only sub-framing, two prevalent types of composite-related materials used in continuous insulation systems are Composite Metal Hybrid (CMH) and Fiber-Reinforced Polymer (FRP). By understanding the differences between these two types of materials, construction experts can determine the best-suited materials for their specific projects, resulting in more efficient and durable structures.

I. Importance of Continuous Insulation Sub-Framing in Building Envelopes

Continuous insulation (CI) sub-framing is a crucial component in designing and constructing energy-efficient building envelopes. It is an uninterrupted layer of insulation that spans all structural members, such as studs and joists, and can effectively minimize thermal bridging. Thermal bridging occurs when heat transfers through the building envelope via conductive materials, leading to increased energy consumption, reduced occupant comfort, and potential condensation issues. By incorporating best practice continuous insulation sub-framing, designers and builders can mitigate these adverse effects and comply with increasingly stringent energy codes and standards.

CI sub-framing not only contributes to thermal performance but can also enhance the structural integrity and longevity of the building envelope. The sub-framing system provides a stable platform for attaching cladding materials while accommodating different movements caused by thermal expansion and contraction. This reduces stress on the building components and prevents damage to the cladding and insulation layers, ensuring long-term durability and reduced maintenance costs.

Overview of CMH and FRP Technologies

Composite metal hybrid (CMH) and fiber-reinforced polymer (FRP) are two innovative technologies that have gained popularity in the construction industry due to their unique properties. CMH combines the structural strength of metal with the thermal efficiency and corrosion resistance of composite materials. This hybrid technology consists of a fiber-reinforced polymer (FRP) profile, such as a Z-girt, paired with steel inserts for fastener retention. Its primary advantages include high structural strength, excellent thermal efficiency, corrosion, and fire resistance, making it ideal for use in building envelopes, particularly in continuous insulation sub-framing.

On the other hand, fiber-reinforced polymer (FRP) is a composite material made by combining polymer resins with reinforcing fibers, such as glass, carbon, or aramid. FRP offers corrosion resistance and thermal resistance. However, FRP has some limitations, such as lower fire resistance, lower structural strength, the potential inclusion of red-list chemicals, and reduced fastener retention compared to CMH.

II. Basics of Composite Metal Hybrid (CMH) Sub-Framing

GreenGirt Composite Metal Hybrid (CMH) continuous insulation sub-framing

Definition and composition:

Composite metal hybrid (CMH) sub-framing represents a cutting-edge solution in the construction industry, combining the best properties of both metal and composite materials to optimize building envelope performance. CMH sub-framing is designed to provide high structural strength, excellent thermal efficiency, and corrosion resistance, making it an ideal choice for continuous insulation systems.

Typically, CMH sub-framing consists of a fiber-reinforced polymer (FRP) Z-profile integrated with steel inserts for fastener retention. This unique composition allows CMH sub-framing to offer the same (or better) loading capabilities as traditional metal Z-girts while eliminating through-wall fasteners and thermal bridging. By incorporating CMH sub-framing in building envelope designs, designers and builders can effectively address the challenges associated with thermal expansion and contraction, ultimately enhancing the durability, energy efficiency, and overall performance of building envelopes.

Main Features:

  • High structural strength: CMH sub-framing offers exceptional load-bearing capabilities comparable to traditional metal Z-girts, ensuring the stability and integrity of building envelopes.
  • High thermal efficiency: CMH sub-framing minimizes thermal bridging by eliminating through-wall fasteners while housing various insulation materials. This results in improved energy efficiency and reduced heat loss through the building envelope.
  • Moisture control: CMH sub-framing’s resistance to moisture and corrosion helps prevent moisture-related issues such as mold growth and material degradation, ensuring the longevity of the building envelope. This feature is essential as moisture control is critical to maintaining the performance and durability of construction projects.
  • High fastener torque retention: Integrating steel inserts within the FRP profile allows for excellent fastener retention, providing a secure connection between the cladding and the sub-framing system.
  • Fire-resistance: CMH materials exhibit a higher fire resistance than standalone FRP, enhancing the overall safety and performance of the building envelope.
  • Durability: The combination of corrosion-resistant FRP and robust steel inserts ensures long-lasting performance, even in harsh environmental conditions, reducing maintenance costs and extending the service life of the building envelope.
  • Ease of installation: CMH sub-framing systems are designed for straightforward installation, allowing for efficient construction processes and reduced labor costs.
  • Overall building health: By optimizing thermal performance and minimizing potential condensation issues, CMH sub-framing contributes to a healthier indoor environment for occupants, promoting overall building health and well-being.

Function and Applications:

The function and application of CMH continuous insulation sub-framing in the construction industry are multifaceted. Its primary function is to provide a stable and efficient platform for attaching cladding materials while minimizing thermal bridging. This is achieved by eliminating through-wall fasteners and incorporating thermal breaks into the sub-framing system. CMH sub-framing can be applied in different building envelope systems, including curtainwalls and rainscreens. Its impressive structural strength and thermal efficiency make it an ideal choice for energy-efficient building projects, minimizing energy consumption and enhancing occupant comfort.

Its excellent corrosion resistance and moisture control properties also ensure the longevity and durability of building envelopes in various environmental conditions. Moreover, CMH sub-framing systems can be easily installed, reducing labor costs and construction time. Finally, its ability to enhance overall building health by improving insulation performance and preventing moisture-related issues further highlights its importance in construction projects. Overall, CMH continuous insulation sub-framing offers a reliable, robust, and versatile solution for building professionals seeking to optimize the performance and sustainability of building envelopes.

III. Basics of Fiber-Reinforced Polymer (FRP) Sub-Framing

Definition and Composition:

Fiber-reinforced polymer (FRP) sub-framing is a composite construction material designed to support and enhance building envelope performance by providing a lightweight and corrosion-resistant alternative to traditional metal sub-framing systems. FRP consists of a polymer matrix, typically made from resin reinforced with glass, carbon, or aramid fibers. This combination results in a lighter weight and corrosion resistance, making FRP an attractive solution for some applications in the construction industry.

Main Features:

  • Low structural strength: In contrast to CMH or metal sub-framing alternatives, FRP exhibits a comparatively lower degree of structural strength. This factor may affect the long-term stability and robustness of a building’s construction.
  • Low fastener retention: FRP sub-framing may exhibit lower fastener retention than metal or CMH alternatives, which could impact the stability and connection of substrate and cladding materials.
  • High thermal efficiency: One of the critical benefits of FRP sub-framing is its thermal performance; if installed properly, it can minimize thermal bridging, reduce energy consumption, and improve overall building envelope efficiency. However, thermal bridging will not be eliminated if through-wall fasteners and through-insulation fasteners are used with the FRP sub-framing.
  • Corrosion resistance: FRP sub-framing is highly resistant to corrosion caused by moisture, chemicals, and environmental factors, making it suitable for use in environments where traditional metal sub-framing may be prone to degradation. However, moisture-related issues can still occur if through-wall fasteners are used with FRP sub-framing. In addition, if energy can travel along the through-wall fasteners, moisture can too.
  • Lighter weight: The lightweight nature of FRP sub-framing allows for easier transportation, handling, and installation, which can contribute to the overall project timeline and expenses.

Function and Applications:

While FRP sub-framing offers various benefits, including thermal efficiency and corrosion resistance, it may not be best suited as a sub-framing material within the building envelope due to its lower structural strength and fastener retention compared to metal or CMH alternatives. However, FRP can still be useful in the construction industry as an alternative non-load-bearing material for cladding, roofs, or floors. Its lightweight nature and high corrosion resistance make it a cost-effective and sustainable option for these applications. Moreover, FRP materials offer design flexibility and aesthetic appeal, giving architects and builders more options for creating visually striking buildings. As with any construction material, proper installation and maintenance are crucial to ensuring its long-term performance and sustainability.

Scientific Explanations and Research Backing

Thermal Expansion Effects on Building Materials

Thermal expansion is an inevitable phenomenon that occurs when building materials experience changes in temperature. As the temperature of materials increases, their particles become more energized and begin to move and expand, leading to a size increase. Conversely, a decrease in temperature leads to a contraction in size. If not managed correctly, these changes in size can lead to several issues, including structural damage, detachment of cladding materials, and compromised insulation performance.

GreenGirt composite metal hybrid (CMH) combines the structural strength of metal with the thermal efficiency and corrosion resistance of fiber-reinforced polymer (FRP), creating a sub-framing solution that effectively manages the challenges associated with thermal expansion.

Scientific studies have identified that incorporating continuous insulation sub-framing systems into building envelopes can significantly reduce the effects of thermal expansion. Furthermore, research has shown that Composite Metal Hybrid (CMH) and Fiber-Reinforced Polymer (FRP) materials can effectively accommodate thermal expansion and contraction while minimizing thermal bridging, improving energy efficiency, and maintaining structural integrity. As a result, adequately designed CMH and FRP sub-framing systems can significantly reduce the impact of thermal expansion, improving the overall performance and durability of constructed buildings.

Sub-Framing Materials in Elevated Building Envelope Service Temperatures

Research conducted in the United States, Canada, and Europe has shown that surface temperatures, even in moderate climates, can reach or surpass 180 degrees Fahrenheit. A study carried out in Germany, which has a climate comparable to Eastern Canada, reveals that building envelope temperatures frequently exceed 176 degrees Fahrenheit.¹ A straightforward yet accurate approach to determining the service temperature of your building envelope is to consider the overall high and low temperatures. In the lower 48 states of the United States, the safe operating range is similar to interior car temperatures, ranging from -40 degrees to 180 degrees Fahrenheit.

If building envelope service temperatures are not considered during the design and construction process, building materials may experience various adverse effects, which can lead to reduced performance, increased maintenance costs, and potentially compromised structural integrity.

When various composite sub-framing materials are exposed to elevated service temperatures, the performance and durability of these materials can be compromised. Studies have analyzed the behavior of CMH and FRP materials under high temperatures, providing valuable insights into their performance and suitability for construction applications.

Figure 1: Pull-Out Strength of Composite Sub-Framing with #14T3 Fasteners

Pull-Out Strength of Composite Sub-Framing with #14 T3 Fasteners

These two materials exhibit different performance characteristics regarding elevated building envelope service temperatures due to their unique compositions and properties. As depicted in the data (Figure 1), increasing service temperature can reduce the fastener pull-out strength of composite sub-framing materials. While both CMH and FRP experience a decline in strength as the temperature rises, CMH maintains its superior strength compared to steel, even under elevated temperatures. Conversely, it is essential to note that although some FRP materials initially demonstrated higher strength than steel at room temperature, they ultimately fell below steel’s strength with exposure to increased temperatures. This data accentuates the impact of thermal expansion on building materials and underscores its significance in construction projects.

In contrast, the behavior of FRP materials at elevated service temperatures varies depending on the type of polymer resin and reinforcing fibers used. While FRP materials generally exhibit excellent corrosion resistance and thermal efficiency, they may not be suitable for applications requiring structural strength at high temperatures. FRP materials can experience reduced stiffness, increased creep deformation, and even degradation of the polymer matrix at elevated temperatures. Furthermore, the likelihood of losing fastener retention is high in FRP sub-framing systems, leading to the detachment of cladding materials and reduced performance.

Research has shown that CMH sub-framing materials outperform FRP materials in terms of structural strength, fastener retention, and thermal resistance at elevated service temperatures. In addition, CMH materials offer greater thermal compatibility with steel inserts, which provide additional strength and stiffness to the overall system while eliminating thermal bridging.

Expert Insights and Recommendations: GreenGirt CMH Sub-Framing

SMARTci GreenGirt

GreenGirt Composite Metal Hybrid (CMH) sub-framing has emerged as a best practice sub-framing solution that provides high structural strength, corrosion resistance, and thermal efficiency. Its unique composition, combining composite Z-profiles with steel inserts, offers the same (or better) loading capabilities as traditional metal sub-framing while minimizing thermal bridging. In addition, GreenGirt’s corrosion resistance and moisture control help prevent issues such as mold growth and material degradation, enhancing the durability and longevity of the building envelope.

Furthermore, its high fastener retention and fire resistance contribute to a secure connection between the cladding and the sub-framing system, increasing overall building safety and performance. GreenGirt sub-framing systems can accommodate various insulation materials, contributing to improved energy efficiency and reduced heat loss through the building envelope. Its ease of installation and straightforward integration into the curtain and rainscreen walls allow for efficient construction processes, reducing labor costs and time.

Overall, GreenGirt CMH sub-framing offers an innovative and versatile solution for building professionals seeking to address the challenges associated with structural integrity and optimize the performance and sustainability of building envelopes.


In conclusion, understanding the differences between composite metal hybrid (CMH) and fiber-reinforced polymer (FRP) sub-framing materials is crucial for building professionals seeking to make informed decisions on building envelope building materials. CMH sub-framing offers high structural strength, thermal efficiency, moisture control, and fire resistance, making it suitable for various continuous insulation applications. On the other hand, FRP sub-framing offers lightweight and corrosion resistance but may present challenges related to fastener retention and lower structural strength.

It is essential to consider the specific requirements of each project, such as building envelope service temperatures, sustainability goals, and local building codes, to determine the most suitable sub-framing material. GreenGirt CMH sub-framing, for example, offers an innovative and versatile solution that addresses these challenges and optimizes the performance and sustainability of building envelopes.

Building professionals should engage with experienced and reputable sub-framing experts to address their project’s specific requirements and make informed decisions on the best-suited materials. To learn more about GreenGirt CMH or to contact us today, please visit our website.


© 2023 Advanced Architectural Products



  1. Bishara, Ayman; Kramberger-Kaplan, Helga; and Ptatschek, Volker. “Influence of Different Pigments on the Façade Surface Temperatures,” Energy Procedia, 2017, No. 132: 447-453.

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