Lightweight Rear-ventilated Rainscreen Façade Thickness 101

Impact of mechanical fastener panel application methods

In a LWRVRS panel façade system, the substructure components are usually aluminum and steel.
In a LWRVRS panel façade system, the substructure components are usually aluminum and steel.

Another consideration affecting panel thickness is the method in which the panel is affixed to the building façade. LWRVRS façades are commonly applied to the building envelope using mechanical fastening methods, such as:

    • exposed fastener – a face-mounted through-fastener (rivet or screw) into a metal support substructure behind the panel, where the fastener head remains visible but is often painted to match the colour of the panel finish; and
  • hidden (aka concealed) fastener – a back-mounted hook-clip attached to the panel using a blind-fastener (the panel with hook-clip is then ‘hung’ on a rail profile behind the panel façade).

Exposed-fastener LWRVRS panel façades are affixed to the continuous vertical metal substructures at the sides of the panels, as well as with intermediate vertical supports in between (i.e. mid-supports), depending on the panel width and deflection limits. Exposed-fastener panel façades are typically installed at a lower cost than hidden-fastener types as they require fewer system components. The former can also be easier to replace as the damaged panels do not require as much façade disassembly to remove.

Hidden-fastener LWRVRS façades use mechanical fasteners to attach a clip to the back of the panel. Depending on the type of fastener, the panel thickness may need to be increased to accommodate the fastener’s application and depth requirements.

Blind fasteners used to affix back-mounted panel clips include:

  • threaded screws, common for phenolic/HPL materials, and require panels that are at least 10 mm (3/8 in.) thick;
  • undercut anchor bolts, common for FRC/GRFC materials, and need panels that are at least 12 mm (½ in.) thick;
  • expanding styled rivet/screw fasteners that can be used with phenolic and FRC/GRFC materials, typically allowing for panels to be as thin as 8 mm (5/16 in.).

Impact of bonded panel application methods

An illustration of a thermally broken assembly with hidden fastener for a LWRVRS façade.
An illustration of a thermally broken assembly with hidden fastener for a LWRVRS façade.

In addition to mechanical fastening, panel façade systems can also be affixed to the building envelope using the advanced bonding methods practiced in modern aerospace and automotive construction industries. Bonding methods (aka dynamic bonding) utilize a polymer adhesive that cures to form a permanent elastic bond between two surfaces, such as between the panel and support clip or rail. Dynamically bonded materials benefit from both the strength of the molecular bond spread out over the surface of the adhesion area as well as the immense elastic resistance provided by the polymer.

A significant advantage to using dynamic bonding for LWRVRS façade applications is the panel material thickness can be thinner than what would otherwise be required for back-mounted mechanical fasteners. A good example is FRC hidden-fastener panels that normally require 12-mm (½-in.) thicknesses to fit the undercut anchor bolts on back-mounted clips. With dynamically bonded back-mounted clips, FRC concealed-fastener panels can be only 8 mm (5/16 in.) thick.

Dynamically bonded application methods also expand the range of even thinner LWRVRS façade materials that can be applied to a hidden-fastener façade system, such as 6 mm (¼ in.) thick PSS with back-mounted support clips.

Impact of panel shape and design

The shape of the panel façade can have an impact on the minimum thickness of the LWRVRS material. If the panel is irregularly shaped, such as triangular with a sharp point or a panel with cut-out shapes (i.e. L-shaped) or notched surfaces, the thickness may need to be increased to ensure sufficient rigidity at the panel stress points as the building settles and shifts throughout its lifespan.

Panels mounted onto a curved surface often require a thinner material thickness to be sufficiently flexible to achieve a smooth bending radius.

Panel thickness and environmental impact

LWRVRS façade materials are designed to resist environmental deterioration for as long as possible. By that very nature, façade materials in landfills will not decompose quickly. Ideally, LWRVRS façade thicknesses should only be as thick as necessary, not only to reduce the embodied energy needed to create the material, but also to limit the amount of material stored in a landfill at the end of its life.

The substructure components supporting the LWRVRS panel façade systems are typically aluminum and steel, highly recyclable materials that are regularly recovered during building demolition.

Conclusion

For many consultants and contractors, LWRVRS façades may still be a relatively new and unfamiliar product. In the author’s opinion, consultants and contractors need to work collectively with LWRVRS technical consultants to ensure their project façade solution is optimized not only for esthetics, but also for efficiency and durability.

Building the façades of the future is a long-term industry initiative to unify the house of construction with the field of design. Maximizing the efficiencies of modern building façade materials helps ensure building owners experience their full benefits, both esthetically and financially.

Ian Gruber, CTR, is technical consultant – Prairies and Northern Regions for Engineered Assemblies. As an architectural technologist, Gruber has facilitated thousands of training hours to clients, architects, and contractors on fenestration and building envelope systems across Canada during his multi-decade career. Gruber can be reached at igruber@engineeredassemblies.com.

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