Ascent - Summer 2025
Precast Concrete Enclosure Systems
Jim Schneider 2025-07-04 12:36:40
TECHNICAL
Precast Concrete Enclosure Systems: THE IDEAL BUILDING SOLUTION
Precast concrete offers quality that can be used in creating high-performance building enclosures
The built environment plays a crucial role in shaping our world, impacting not only the physical landscape but also the health, safety, and well-being of its occupants. Americans spend 90% of their lives indoors, according to the U.S. Environmental Protection Agency. It is the responsibility of those in the architecture, engineering, and construction community to design, build, and maintain buildings that best support the health of occupants and the surrounding environment.
The demand for buildings that are strong, sustainable, and safe has never been greater. The building enclosure, which serves as the primary interface between the interior and exterior environments, is an important point of emphasis in this effort. Precast concrete offers quality that can be used in creating high-performance building enclosures.
Precast Concrete Enclosure Systems: Types and Applications
Precast concrete enclosure systems offer a solution for the design of high-performance building envelopes. Wall panels are produced off-site in a manufacturing facility under controlled conditions that provide a great deal of control over materials, mixture proportions, and quality. There are three basic types of precast concrete enclosure systems: solid wall panels, insulated sandwich wall panels, and thin-shell cladding, each with unique characteristics and applications.
Single-wythe panels are solid precast concrete panels that serve as both the structural and architectural components of the building enclosure. They are typically 3 to 8 in. thick. Single-wythe precast concrete panels are often used with an interior furring system to allow installation of additional insulation and utilities, though there is the potential to have an exposed concrete finish on the interior. Single-wythe panels are used in a variety of applications, including commercial structures, industrial buildings, and warehouses.
Double-wythe insulated panels, also known as insulated sandwich wall panels, consist of two concrete wythes of precast concrete, prestressed concrete separated by a layer of insulation. The thicknesses of the concrete wythes and the insulation layer vary depending on the design of the wall panel and its performance requirements. The wythes are typically connected by a series of ties or mesh made from a nonconductive material, such as carbon fiber or fiber composite, to eliminate thermal bridging (Fig. 1).
Using metal pins or ties of any kind, as can be the case in some traditional brick cavities, creates thermal bridges through the assembly. Any metal will create cold spots or short circuits that impact the thermal efficiency of the assembly, per the American Society of Heating, Refrigerating and Air-Conditioning Engineers’ Standard 90.1, Energy Standard for Sites and Buildings Except Low-Rise Residential Buildings. As the thermal imaging in Fig. 2 shows, a precast concrete sandwich wall panel provides continuous insulation free of thermal bridges, which prevents thermal energy from passing through the wall.
Precast concrete insulated sandwich wall panels are generally classified as composite or noncomposite based on design methodology and connection devices used between the two concrete wythes. In composite panels, the concrete wythes work together as one wall to carry the load. Alternatively, in noncomposite panels, the concrete wythes work independently, often with the interior wythe being thicker to carry the load, while the exterior wythe has an architectural finish (Fig. 3).
Composite panels of a given total thickness of concrete wythes will have nearly the same stiffness and strength as solid concrete panels of the same thickness. Noncomposite panels will have about the same stiffness and strength as the sum of the stiffness and strength values for the individual concrete wythes.
For similar panel geometries, partially composite walls have stiffness values greater than those of noncomposite panels and less than those of composite panels. They also have strengths that are greater than those of noncomposite panels and less than or equal to those of composite panels.
Thin-Shell Precast Concrete
Where precast concrete serves in a primarily architectural capacity, lighter-weight thin-shell panels are used in cavity wall systems. This type of application uses approximately 1½ to 3-in.-thick pre-cast concrete panels as the exterior cladding, hung on a separate interior wall structure that is often made from cast-in-place concrete or steel.
This type of assembly typically consists of an exterior thin-shell precast concrete panel separated from the interior wall by an air cavity, creating a multilayer system. This cavity serves as a drainage plane and can house insulation, though insulation can alternatively be installed on the interior wall itself. The air space allows water that penetrates the exterior to drain away through weep holes while also providing ventilation. For this system to function effectively, proper moisture management is essential and includes features like appropriate flashing, weep holes, and moisture barriers to prevent water damage and promote drying.
While there are height limitations due to weight for the other types of precast concrete wall systems (typically 10 to 12 stories), thin-shell precast concrete can be used on taller buildings because it works in tandem with another material framing assembly. For this reason, thin-shell applications often include high-rise buildings, commercial structures, institution facilities, and healthcare establishments.
Energy Efficiency, Indoor Environmental Quality
Thermal mass is the ability of a material to absorb, store, and release heat. Precast concrete, with its high density and specific heat capacity, exhibits excellent thermal mass properties. This plays a significant role in the performance of precast concrete enclosure systems.
The thermal mass effect contributes to building performance in several ways:
• Temperature stabilization: Thermal mass absorbs heat during warm periods and releases it during cooler periods, helping to stabilize indoor temperatures.
• Peak-load shifting: By delaying heat transfer, thermal mass can shift peak cooling loads to off-peak hours, reducing energy costs and strain on heating, ventilating, and air-conditioning (HVAC) systems.
• Passive solar design: Thermal mass can be used to capture and store solar heat, reducing heating requirements.
• Reduction of temperature swings: The heat-absorbing capacity of thermal mass helps dampen temperature fluctuations, improving occupant comfort.
The impact of thermal mass on building performance can be quantified through the concept of effective R-value. Unlike the material R-value of insulation materials, the effective R-value of a precast concrete wall system accounts for the dynamic thermal performance provided by thermal mass.
Determining effective R-value involves complex thermal modeling that considers factors such as climate zone, building orientation, wall composition, occupancy patterns, and HVAC operation schedules. Studies have shown that the effective R-value of a precast concrete wall system can be significantly higher than its nominal R-value, particularly in climates that experience substantial daily temperature swings.
For example, a thermal mass calculation was conducted on a project in Fresno, Calif., that employed precast concrete insulated sandwich wall panels. The wall system had a material R-value of 11.33. However, when thermal mass was incorporated in the calculation, the wall system performed at an R-value of 26.10. This significant increase in R-value allowed that project team to downsize the building’s HVAC equipment by 37% in tonnage.
To maximize the benefits of thermal mass in precast concrete enclosure systems, designers can:
• optimize the thickness and composition of concrete layers to balance thermal mass and insulation requirements;
• carefully consider the position of insulation within the panel to allow the concrete to interact with the interior environment;
• use appropriate finishes and colors to enhance solar heat absorption or reflection based on climate needs;
• design HVAC systems to work in conjunction with the thermal mass effect, such as nighttime precooling strategies.
The benefits provided by the thermal mass of a precast concrete envelope system will vary according to the conditions, but as it is an inherent quality of the material, it is worthwhile for project teams to assess and run the calculation for potential thermal mass performance.
Sustainability Considerations
As greenhouse gas emissions become a larger part of the conversation, questions arise about concrete, which accounts for 8% to 10% of annual global carbon dioxide (CO2) emissions. This is partly because it is the most used human-made material on Earth, but also due to its material ingredients.
Most of concrete’s CO2 impact comes from using portland cement—the binder in the concrete. For many years, the industry has argued that concrete’s impact is all up front, and once manufactured, it is essentially inert from an emissions standpoint. So, when the initial impact is spread out over a long life cycle, that reduces the impact from cradle to grave.
Still, there is recognition that CO2 reduction must happen now, so currently available measures to decrease concrete’s impact should be considered. For one, using supplementary cementitious materials such as fly ash to partially replace the cement can lower the impact. There are also offset technologies that inject industrial waste CO2 into concrete to entomb it there.
Newer types of cement, such as portland limestone cement, which offers some CO2 emission reductions, are becoming more common. Developing technologies, such as limestone calcinated clay cement, promise to deliver even greater reductions in the future. Innovations abound, and a great deal of investment is going into finding suitable and scalable replacements for cement in concrete.
This article is based on a presentation the author gave at the IIBEC (International Institute of Building Enclosure Consultants) International Convention and Trade Show in March 2025.
Jim Schneider is executive director of the PCI Mountain States chapter. Email jschneider@pcims.org.
©Precast Prestressed Concrete Institute. View All Articles.