Understanding Exterior ACM Wall Assembly

The exterior wall system is tasked with managing and controlling the movement of heat, air and moisture into and out of the building enclosure, while providing the requisite structural support for the exterior façade. To accomplish this extensive list of interrelated, but diverse, design objectives, the exterior wall assembly includes a number of stand-alone components and systems that must work simultaneously and in close proximity with one another without interfering.

Information on ACM’s basic components and systems

By Shawn Crouthamel

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A few of the basic components and systems commonly found in an exterior wall assembly include: structural elements, drainage plane (air and water barrier), vapor retarder (as required), insulating elements, and exterior cladding (specifically for this article: aluminum composite material (ACM) wall panel assembly).

Structural Elements

The structural elements inside of the exterior wall system include the structural supports that attach the veneer, or other types of exterior cladding, to the structure. Building codes require that these structural elements be designed to support the self-weight of the veneer and to withstand appropriate environmental loads, such as wind loads. Structural elements include, but are not limited to, the primary wall structure, sheathing, secondary framing system elements (e.g., cold-formed metal furring), and other structural members that are specific to certain proprietary exterior wall systems.

Drainage Plane

The drainage plane in an exterior wall assembly exists to effectively manage moisture, but is regularly called upon to manage airflow as well. For most ACM systems, the drainage plane is defined with an air and water barrier, an element designed to manage water and airflow at the same plane within the exterior wall assembly. The water barrier is designed to limit exposure of the wall assembly to bulk rainwater and condensation while the air barrier is intended to control the airflow between the outdoors and the interior, conditioned space.

Vapor Retarder

Moisture, in any form, needs to be effectively managed in the built environment. A vapor retarder impedes the flow of water vapor between the exterior assembly and interior walls. The code defines when a vapor retarder is required, and it is oftentimes incorporated into the drainage plane by using a product that can function as a water barrier, air barrier and a vapor retarder.

Insulating Elements

Insulating elements in the exterior wall system manage the flow of heat in and out of the building. This reduces the heat lost or gained through the exterior wall and improves the overall performance of the HVAC system because less energy is required to keep the building at its preferred temperature.

Exterior Cladding (ACM)

Exterior cladding refers to the protective layer or finish affixed to the exterior side of the building envelope. The exterior cladding makes an important contribution to the overall aesthetics of the building, but also provides the first layer of protection against bulk rainwater penetration. Exterior wall assemblies must be designed to meet code-required structural support, continuous insulation, moisture management and fire-resistance performance criteria.

Core Materials in ACM Panels

ACM panels are constructed of three layers—a thin aluminum skin bonded to a low-density core. There are various types of cores used for ACM panels, including corrugated polypropylene, solid polyethylene and aluminum honeycomb:

• Corrugated polypropylene core panels are constructed of two sheets of aluminum bonded to a core of extruded thermoplastic manufactured in a laminated batch (i.e., discontinuous) process using adhesive(s) between dissimilar materials.

• Solid polyethylene core panels are constructed of two sheets of aluminum sandwiching a solid core of extruded thermoplastic material formed in a continuous process with no glues or adhesives between dissimilar materials. The panels are typically available in a polyethylene (PE) or fire-retardant (FR) core.

• Aluminum honeycomb core panels are constructed of two sheets of aluminum bonded to an aluminum honeycomb core.

ACM panels are non-absorbent, water-resistant and simple to maintain. They have a strong and durable surface finish for interior and exterior wall surfaces. The panels are flexible, lightweight and easy to fabricate allowing for innovative design with increased rigidity and strength. The cost, durability and efficiency, as well as being available in a very wide range of colors and finishes, allows for endless design options.

Shawn Crouthamel is the national sales manager for Laminators Inc., Hatfield, Pa. To learn more, visit

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